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Really interesting interactive map navigator!

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Letter size Titanoboa (transparent png)
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Letter size Purussaurus (transparent png)
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Letter size Megalodon (transparent png)
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Letter size Smilodon (transparent png)
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Letter size M. Primigenius (transparent png)
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Letter size Megatherium (transparent png)
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Titanoboa Skeleton

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Purussaurus Skull

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Megalodon Skeleton

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Smilodon Skeleton

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Deinosuchus Skeleton

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Primigenius Skeleton

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Megatherium Skeleton

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A quick guide to carbon dating

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What is Radiocarbon Dating?

Radiocarbon dating is a method of what is known as "Absolute Dating". Despite the name, it does not give an absolute date of organic material - but an approximate age, usually within a range of a few years either way. The other method is "Relative Dating" which gives an order of events without giving an exact age (1): typically artefact typology or the study of the sequence of the evolution of fossils.

There are three carbon isotopes that occur as part of the Earth's natural processes; these are carbon-12, carbon-13 and carbon-14. The unstable nature of carbon 14 (with a precise half-life that makes it easy to measure) means it is ideal as an absolute dating method. The other two isotopes in comparison are more common than carbon-14 in the atmosphere but increase with the burning of fossil fuels making them less reliable for study (2); carbon-14 also increases, but its relative rarity means its increase is negligible. The half-life of the ¹⁴C isotope is 5,730 years, adjusted from 5,568 years originally calculated in the 1940s; the upper limit of dating is in the region of 55-60,000 years, after which the amount of ¹⁴C is negligible (3). After this point, other Absolute Dating methods may be used.

Today, the radiocarbon-14 dating method is used extensively in environmental sciences and in human sciences such as archaeology and anthropology. It also has some applications in geology; its importance in dating organic materials cannot be underestimated enough. In 1979, Desmond Clark said of the method "we would still be foundering in a sea of imprecisions sometime bred of inspired guesswork but more often of imaginative speculation" (3).

Radiocarbon dating may only be used on organic materials. Typically (6):

Wood and charcoal

Seeds, spores and pollen

Bone, leather, hair, fur, horn and blood residue

Peat, mud and soil

Shells, coral and chitin

Pottery (where there is organic residue)

Wall paintings (as they usually contain organic material such as crushed fruit and insects)

Paper and parchment

The above list is not exhaustive; most organic material is suitable so long as it is of sufficient age and has not mineralised - dinosaur bones are out as they no longer have any carbon left. Stone and metal cannot be dated but pottery may be dated through surviving residue such as food particles or paint that uses organic material (8).

There are a number of ways to enter into a career in studying radiocarbon dating. Typically, a Master's Degree in chemistry is required because of the extensive lab work. Increasingly though, students are learning about the principles of radiocarbon dates in archaeology, palaeontology and climate science degrees and can combine cross-disciplinary studies.

History of Radiocarbon-14 Dating

The method developed in the 1940's and was a ground-breaking piece of research that would change dating methods forever. A team of researchers led by Willard F. Libby calculated the rate of radioactive decay of the ¹⁴C isotope (4) in carbon black powder. As a test, the team took samples of acacia wood from two Egyptian Pharaohs and dated them; the results came back to within what was then a reasonable range: 2800BC +/- 250 years whereas the earlier independent dates (largely the dendrochronology records) were 2625 +/- 75 years (3), (5). Archaeologists had used Relative Dating methods to calculate their reigns. Though their initial calculations were slightly incorrect thanks to the contaminants of extensive nuclear testing of the age, scientists soon discovered the error and developed methods that were more accurate, including a date of calibration to 1950. This new method was based on gas and liquid scintillation counting and these methods are still used today, having been demonstrated as more accurate than Libby's original method (3). Willard Libby would receive a Nobel Prize for Chemistry in 1960.

The next big step in the radiocarbon dating method would be Accelerated Mass Spectrometry which was developed in the late 1980s and published its first results in 1994 (3). This was a giant leap forward in that it offered far more accurate dates for a far smaller sample (9); this made destruction of samples a far less delicate issue to researchers, especially on artefacts such as The Shroud of Turin for which accurate dates were now possible without damaging a significant part of the artefact. AMS counts the quantity of ¹⁴ C in a sample rather than waiting for the isotope to decay; this also means greater accuracy readings for older dates.

How it Works

The ¹⁴C isotope is constantly formed in the upper atmosphere thanks to the effects of cosmic rays on nitrogen-14 atoms. It is oxidised quickly and absorbed in great quantities by all living organisms - animal and plant, land and ocean dwelling alike. When an organism dies, it stops absorbing the radioactive isotope and immediately starts decaying (7). As previously mentioned, the half life of the ¹⁴C isotope is 5,730 years - this means that it takes 5,730 years to reach half the radioactivity that the organism had at the point of death, another 5,730 years to reach 25% radioactivity it had at the point of death and so on. Radiocarbon dating is simply a measure of the level of ¹⁴C isotope within the organic remains (8). This is not as clear-cut as it seems as the amount of ¹⁴ C isotopes in the atmosphere can vary. This is why calibration against objects whose age is known is required (14).

AMS works slightly differently; it converts the atoms of the sample into fast-moving ions so that they become charged atoms. By applying magnetic and electrical fields, the mass of these ions is measured and the accelerator is used to remove ions that might contaminate the dating. The sample passes through several accelerators in order to remove as many atoms as possible until the ¹⁴C and some ¹²C and ¹³C pass into the detector. These latter atoms are used as part of the calibration process to measure the relative number of isotopes (9).

How is a Date Calibrated?

When the half-life was corrected in 1950, the year was taken as a base date from which to calculate all resulting dates. Therefore, any expression of "before present" will mean "before 1950". It is presumed that the proportion of atmospheric ¹⁴C is the same today as it was in 1950 (10), (11) and that the half-life remains the same. If a radioactivity level comes back as half of what would have been expected if the organism had died in 1950, then it is presumed to be 5,730 years before 1950. This does not mean that we have a precise year of 3780BC, it means we then need to calibrate through other methods that will show us how atmospheric concentrations of the ¹⁴C isotope has changed - most typically through the dendrochronology records (tree ring data) (10). Very old trees such as North American Bristlecone Pine are ideal for constructing long and accurate records of the state of the atmosphere. This allows researchers to account for variation by comparing the known records of ¹⁴C levels in the tree record, looking for a tree record that has the same proportion of radiocarbon. The overlapping nature of the tree records means this is the most accurate record we have. There will of course be several possible calendar years within the expected range, which is why radiocarbon dates come with a variation such as +/- 25 years for example (11).

Radiocarbon-14 Dating in Action

Archaeology was one of the first, and remains the major, disciplines to use radiocarbon dating and this is why many enter into the lab through combining chemistry and archaeological studies. It has a greater impact on our understanding of the human past than in any other field.

Radiocarbon dating is profoundly useful in archaeology, especially since the dawn of the even more accurate AMS method when more accurate dates could be obtained for smaller sample sizes. One good example is a critical piece of research into the diet of the fragile Viking colonies of Greenland (13) for example; the study examined not just the ¹⁴C dates of the people in the graves, but was also in examining their diet through examining the carbon isotopes themselves. The study concluded dates that were already suspected but not confirmed: that the colony was occupied between the late 10 th century and the early 12 th century. Radiocarbon AMS was also used to calculate when the last Vikings departed Greenland (17).

There has been much debate about the age of The Shroud of Turin. It has become an important relic for many Catholics. The debate raged on for the decades after its discovery. Experts pointed to its medieval design, depiction of Christ and several other key factors marking it as in the region of 700 years old. It wasn't until 1988, and several subsequent tests since then, that this was confirmed (14); it is now the best-known example of the success of the AMS method as countless tests have been carried out and confirmed the dates. A significant portion of the Shroud would have been destroyed using the older method. The paper for the 1988 study is available online (15). Each subsequent test has come back with dates of the mid 14 th century.

Landscape Archaeology is a bridge between archaeology and environmental sciences though many consider it an environmental science in its own right. It is the study of how people in the past exploited and changed the environment around them. Typically, this will involve examining spores and pollen to examine when land was cleared of scrub and trees in the Neolithic Revolution to make way for crops. It also makes use of phytoliths, entomological remains, GIS (digital mapping), soil sampling, bone analyses, ground penetrating radar, and map studies and other documentary data. It has been fundamental, especially in Europe, to demonstrating how landscapes are relics and monuments in themselves and are worthy of study as such. Returning to the example of the Vikings in Greenland above, the extended study and dating of the faunal remains shows distinct changes that were made by the Vikings. The studies show the approximate date of arrival of European livestock and crops (13) and when these finally disappeared from the record (17). Studies such as this are fundamental to determining not just how the environment has changed thanks to human manipulation, but also to natural changes due to fluctuations in the environment and climate.

The practical uses of radiocarbon dating in climate science covers similar examples to the archaeological examples seen above (changes in fauna and vegetation for example) but it is fundamental in other areas too (12). Most critically, it is used when studying ice core date in determining the composition of the climate of the past. Many hundreds of ice samples have been taken in Antarctica and this is fundamental to understanding how we are changing the climate today, and how it may change in future when accounting for fluctuations in atmospheric carbon (18). There are complications however and researchers check the known ice records against any new samples, taking into consideration known ice dates in factoring in their margin of error. Atmospheric composition, the amount of ice coverage at a given time... all of these factors are important in examining past climates (19).

Phytolith studies (fossilised plant remains), entomology (study of insects) as well as the previously mentioned studies of pollen and spores can not only show how an environment changed and what caused it (human engineering or environmental change), but also when the changes occurred.

Sources

http://paleobiology.si.edu/geotime/main/foundation_dating2.html

http://www.skepticalscience.com/history-climate-science.html

http://www.c14dating.com/int.html

http://www.physics.arizona.edu/ams/education/rcarbon_history.htm

http://hbar.phys.msu.ru/gorm/fomenko/libby.htm http://www.sciencemag.org/content/110/2869/678

http://www.radiocarbon.com/about-carbon-dating.htm

http://www.c14dating.com/k12.html

https://c14.arch.ox.ac.uk/embed.php?File=dating.html

https://c14.arch.ox.ac.uk/embed.php?File=ams.html

https://c14.arch.ox.ac.uk/embed.php?File=calibration.html

http://www.c14dating.com/agecalc.html

http://www.aip.org/history/climate/Radioc.htm

Arneborg, J., Heinemeier, J., Lynnerup, N., Nielsen, H.L., Rud, N., Sveinbjörnsdóttir, A. E.: 1999: CHANGE OF DIET OF THE GREENLAND VIKINGS DETERMINED FROM STABLE CARBON ISOTOPE ANALYSIS AND 14C DATING OF THEIR BONES. Radiocarbon 41 (2): p157-168 (http://natmus.dk/fileadmin/user_upload/natmus/forskning/dokumenter/SILA/Projects/radiocarbon.pdf)

http://nvlpubs.nist.gov/nistpubs/jres/109/2/j92cur.pdf

shroud.com/nature.htm

Erika Martin Seibert. "Archaeology and Landscape" (http://www.nps.gov/nr/publications/guidance/NR_workshop_3-11-09/Archeol_and_landscapes_Erika.doc)

Arneborg, J., Heinemeier, J., Lynnerup, N., Nielsen, H. L., Rud, N., Sveinbjornsdottir, A.E., 2002: C-14 dating and the disappearance of Norsemen from Greenland. Europhysics News 33 (3), 77-80 (http://www.europhysicsnews.org/articles/epn/pdf/2002/03/epn02301.pdf)

https://journals.uair.arizona.edu/index.php/radiocarbon/article/viewFile/1487/1491

http://onlinelibrary.wiley.com/doi/10.1029/2009JD011860/full

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Radiocarbon dating is a method of what is known as "Absolute Dating". Despite the name, it does not give an absolute date of organic material - but an approximate age, usually within a range of a few years either way.

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Ever since the Museum's Earth History Gallery opened in the early 1970s, visitors have been struck by the appearance of a giant skeleton near the end of the gallery. Many children (and perhaps more than a few adults) have thought that it is a dinosaur, but it is in fact a mammal from the much more recent past, a replica of the giant ground sloth Megatherium americanum. Megatherium was a huge ground-dwelling creature, distantly related to the modern tree sloths. Ground sloths were a very successful group, with fossils known from many parts of South and North America (including western Canada), but sadly they disappeared in the Pleistocene megafaunal extinctions, along with other wondrous creatures such as the woolly mammoth and short-faced bear. There are many different ground sloths known, but Megatherium was the largest, described as " weighing up to eight tons, about as much as an African bull elephant." It walked on all fours (with a gait similar to that of a giant anteater), but could rise on its hind legs, supported by the huge tail, to browse on the trees that apparently formed the main part of its diet. Our sloth is shown in this sort of pose, though it lacks a tree at present. Although ground sloths lived across both American continents, itself is known only from South America. Our plaster cast of a Megatherium skeleton is, of course, much newer than the Pleistocene. But it is very old in human terms, so remarkably old that it could be considered as an artifact of a long-past scientific age. It is far older than our current Museum building, much older than the first Manitoba Museum that was located in the Winnipeg Auditorium, older than the Manitoba Legislative Building; in fact it is nearly the same age as the Province of Manitoba! The Megatherium and its close colleague the armoured glyptodont have been companions for a century or more, and both arrived at our Museum by a circuitous path.

But let me begin the sloth's tale at its beginning. Megatherium is among the best known of ground sloths, with dozens of fossils collected in South America and shipped to Europe from the 18th Century onward. Many specimens apparently came from the banks of the Luján River near Buenos Aires, Argentina, and were in collections and on exhibit in cities such as Paris, Madrid, and London. The first formal scientific description was produced by the great French scientist Georges Cuvier, in 1796. In the 1850s, a young American scientist, Henry Augustus Ward, made a detailed study of Megatherium, visiting collections in Paris and London among many other places. After his return to Rochester, New York, he became a professor at the University of Rochester, but also founded Ward's Natural Science Establishment, a company that sold scientific specimens, replicas, and materials. Ward got started on the casting and selling of fossil skeletons very early. His company was among the first to produce casts for sale to the many new natural history museums that were then being developed, and the giant Megatherium was one of his "star attractions." His catalogue advertised that a full skeleton consisting of 124 different casts could be purchased for $250, "packed not painted" but including a replica tree. In Montreal, a museum for McGill University was planned from the 1860s onward, to exhibit collections developed by the world-famous Professor William Dawson. This facility, funded by and named for the industrialist Peter Redpath, was opened in 1882. It was primarily to serve as a resource for the university's faculty and students, but secondarily for the education of the people of Montreal. Dawson had long corresponded with Ward concerning the acquisition of particular items, so it is not surprising that a description of the original museum includes:

"Entering the Redpath Museum, the visitor saw at the back of the ground floor a handsome lecture theater with seats for 200 students... To the right of the entrance, a staircase ... led to the main floor or "Great Museum Hall." Henry Ward's imposing cast of the British Museum's megatherium (a giant sloth)--set up by his partner Howell and a status symbol for new museums--distinguished this floor, which displayed paleontological, mineralogical, and geological specimens."
The Redpath today is a wonderful old-fashioned natural history museum, but it is also rather pocket-sized in comparison with the huge museums of Europe. The Megatherium occupied a considerable proportion of its limited floor space. Several years later, it was joined by the armoured glyptodont, also apparently supplied by Ward's. Thus, that museum's main hall was dominated by replicas of giant extinct mammals. But how did these fascinating and historic replicas become migrants once again, moving westward from Montreal to Winnipeg? In the 1960s there must have been a push to add other creatures such as a dinosaur to the Redpath's exhibits, and the only way to do this was to replace the large pieces that filled its space (that part of the Redpath is now occupied by a tyrannosaurid dinosaur, among other exhibits). According to what my predecessor Dr. George Lammers told me, the Redpath was looking for a home for these enormous casts, and this just happened to come at a time when The Manitoba Museum was constructing its new building, with plenty of square footage that needed to be filled. So the skeleton casts were transferred to our Museum, and they were crated and shipped to Manitoba. On arrival at the Museum, the replicas were uncrated and examined. George told me that some repair was required as a result of damage in transit, and apparently the plaster bones were found to be stuffed with Reconstruction Era American newspapers! The Megatherium was re-mounted in a slightly different posture, and sadly lacks the "tree" on which it had appeared to browse for ninety years or so. But at least it had its friend, the glyptodont, nearby, and they seem to have happily settled into their new home, impressing (and sometimes scaring) the millions of children who have visited our Museum in the past forty years. The name of our sloth is a bit complicated. The note that George left me calls it Megatherium cuvieri. This is what Ward had called it, and it was probably labelled as such when on exhibit at the Redpath. The species name "cuvieri" was, however, apparently based on a misguided attempt in the 1820s to re-brand Cuvier's perfectly valid Megatherium americanum. Modern rules of taxonomic usage consider cuvieri to be a nomen illegitimum ("illegitimate name"), so we can safely call it M. americanum. Given this cast's critical role in the history of exhibits at two of Canada's most important natural history museums, and its place in the story of the development of North American paleontology, what is the future of our sloth? Since we have been progressing with a gradual refurbishment of the Earth History Gallery, I would like to soon plan new interpretive materials that explain the tremendous story and significance of this exhibit. But in the somewhat longer term, wouldn't it be wonderful if it could be re-mounted and given back its "tree," perhaps serving a new role as the centrepiece for a larger exhibit of extinct ice age animals?

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Ever since the Museum's Earth History Gallery opened in the early 1970s, visitors have been struck by the appearance of a giant skeleton near the end of the gallery. Many children (and perhaps more than a few adults) have thought that it is a dinosaur, but it is in fact a mammal from the much more recent past, a replica of the giant ground sloth Megatherium americanum.

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Megatherium/Ground sloth general info and references

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Name: Megatherium ‭(‬Giant beast‭)‬.
Phonetic: Meg-ah-fee-ree-um.
Named By: Georges Cuvier‭ ‬-‭ ‬1796.
Classification: Chordata,‭ ‬Mammalia,‭ Xenarthra, ‬Pilosa,‭ ‬Megatheriidae.
Species: M.‭ ‬americanum‭ (‬type‭)‬, ‭ ‬M.‭ ‬altiplanicum,‭ ‬M.‭ ‬gallardoi,‭ ‬M.‭ ‬istilarti,‭ ‬M.‭ ‬medinae,‭ ‬M.‭ ‬parodii,‭ ‬M.‭ ‬sundti,‭ ‬M.‭ ‬altiplanicum.
Diet: Primarily a herbivore,‭ ‬but possibly omnivorous.
Size: 6‭ ‬meters long.
Known locations: South America.
Time period: Zanclean of Pliocene through to end of Pleistocene/start of Hologene.
Fossil representation: Many fossil specimens allowing for complete reconstruction.

With the possible exception of the woolly mammoth‭ ( ‬Mammuthus primigenius‭)‬,‭ ‬Megatherium is arguably the most famous of the giant mammals that once roamed this planet after the decline of the dinosaurs.‭ ‬Megatherium was also one of the last to disappear with remains appearing in the fossil record until as recently as the start of the Hologene,‭ ‬the period that has seen the rise of mankind and the dawn of civilisation.
Aside from its large size,‭ ‬Megatherium's skeleton is extremely robust in its construction,‭ ‬and seems to be built not just to support its large body but to provide the maximum amount of stability.‭ ‬The lower bones of the short hind legs are comparable to the femur in thickness and development.‭ ‬Combined with a short but thick tail and a broad pelvis,‭ ‬the lower body effective becomes a seat for which the upper body can rest on.‭ ‬The price of this lower body development is that Megatherium certainly would not have broken any records for speed,‭ ‬and may have been one of the slowest animals in its ecosystem.‭ ‬However this would not be a problem as Megatherium probably would not have had to run to or from anything.
The upper body construction is along similar lines in its robust build,‭ ‬but has more of a focus upon flexibility.‭ ‬The arms are still built solid and strong for weight bearing,‭ ‬but they are also much longer to provide additional reach.‭ ‬This reach would have also been increased even further by the large claws on its hands,‭ ‬allowing taller branches and foliage to be brought down to the level of the mouth.‭ ‬The strong jaw is an adaptation more suited for mashing plant material though a combination of strong muscle attachment and robust molar teeth.
The most classic posture that fossil remains and artistic renderings of Megatherium are posed in is of a large shaggy coated sloth that is rearing up on its hind legs.‭ ‬However,‭ ‬even though Megatherium was certainly capable of shifting its weight to its hind legs,‭ ‬and even walking on just the hind legs as indicated by fossil footprints,‭ ‬Megatherium probably adopted a quadrupedal posture when resting and normally walking extended distances.‭ ‬Aside from Megatherium's large body making a quadrupedal posture more stable for weight distribution,‭ ‬the large claws on its hands and feet meant that it had to walk on the‭ ‬sides,‭ ‬and not the flats of its feet.

What did Megatherium eat‭?
Continuing studies about Megatherium and giant ground sloths in general,‭ ‬have yielded a number of theories as to its diet.‭ ‬One thing which is absolute is that Megatherium would have eaten plants like other giant ground sloths and would have used its large size to reach up into trees to pick out vegetation that was beyond the scope of smaller herbivores.‭ ‬This meant that competition for food between giant ground sloths like Megatherium and other herbivores was comparatively low,‭ ‬and is one of the reasons why giant ground sloths were able to spread upwards into North America when it became connected to South America during the Pliocene.
Megatherium would have used its ability to walk on just its hind legs to reach further up,‭ ‬where it could use its large claws to pull down branches towards its mouth.‭ ‬Megatherium is also thought to have had a long tongue which it could then use to wrap around the branches,‭ ‬stripping off leaves and soft fresh growth.‭ ‬However,‭ ‬just because Megatherium could reach up high to feed,‭ ‬it does not mean that it only fed this way.‭ ‬Megatherium would have been quite capable of feeding upon lower vegetation,‭ ‬and here it may have used its claws for digging at plant roots.‭ ‬The strong teeth and robust jaw‭ ‬suggest that Megatherium was quite capable of chewing tough vegetation,‭ ‬and this adaptation further suggests that Megatherium was capable of adapting to different plant types.
A more controversial theory about Megatherium's diet is the inclusion of meat.‭ ‬Although generally considered a herbivore,‭ ‬Megatherium has‭ ‬also been portrayed as an occasional scavenger of carcasses,‭ ‬even driving off predators from their kills.‭ ‬This idea is centred around the theory that Megatherium,‭ ‬and possibly other giant ground sloths,‭ ‬may have needed to supplement their diet with meat in order to obtain nutrients that were lacking in their usual herbivorous diet.‭ ‬By approaching carcasses they could feed out of opportunity rather than actively aggressing against other animals.‭ ‬The massive size and power of its body would have also worked in Megatherium's favour,‭ ‬making it virtually immune to attack from the much smaller predators of the time.
However,‭ ‬some have gone even further than just the scavenger theory and have even suggested that Megatherium could actively hunt and attack other animals if it was so inclined.‭ ‬The idea for this has been based upon the possibility of Megatherium attacking glyptodonts‭ (‬armadillo like herbivores‭ ‬such asDoedicurus‭)‬,‭ ‬flipping them over and then killing them with its claws.‭ ‬While the mechanics of this scenario are quite easy to imagine,‭ ‬the actual motivation for it has been too much for most palaeontologists to believe.‭ ‬Unless new fossil evidence and/‭ ‬or new study proves otherwise,‭ ‬Megatherium continues to be regarded as an exclusively,‭ ‬or at the very least primarily herbivorous animal.

Further reading
- Nuevos restos de mamferos fsiles Oligocenos recogidos por el Profesor Pedro Scalabrini y pertenecientes al Museo Provincial de la ciudad del Parana. - Boletn de la Academia Nacional de Ciencias de Crdoba 8:1-205. - F. Ameghino - 1885.
- Juan Bautista Bru (1740-1799) and the description of the genus Megatherium. - Journal of the History of Biology 21 (1): 147-163. - J. M. L. Piero - 1988.
- Bipedalism and quadrupedalism in Megatherium: An attempt at biomechanical reconstruction. - Lethaia 29: 87-96. - A. Casinos - 1996.
- Megatherium, the stabber. - Proceedings of the Royal Society of London 263 (1377): 1725-1729. - R. A. Faria & R. E. Blanco - 1996.
- The smallest and most ancient representative of the genus Megatherium Cuvier, 1796 (Xenarthra, Tardigrada, Megatheriidae), from the Pliocene of the Bolivian Altiplano. - Geodiversitas 23(4):625-645. - P. A. Saint-Andre & G. De Iuliis - 2001.
- The ground sloth Megatherium americanum: Skull shape, bite forces, and diet. - Acta Palaeontologica Polonica 46 (2): 173-192. - M. S. Bargo - 2001.
- Mamferos extintos del Cuaternario de la Provincia del Chaco (Argentina) y su relacin con aqullos del este de la regin pampeana y de Chile. - Revista geolgica de Chile 31(1):65-87. - A. E. Zurita, A. A. Carlini, G. J. Scillato-Yan & E. P. Tonni - 2004.
- A new species of Megatherium (Mammalia: Xenarthra: Megatheriidae) from the Pleistocene of Sacaco and Tres Ventanas, Peru. - Palaeontology 47(3):579-604. - F. Pujos and R. Salas - 2004.
- Megatherium celendinense sp. nov. from the pleistocene of the Peruvian Andes and the phylogenetic relationships of Megatheriines. - Palaeontology 49(2):285-306. - F. Pujos - 2006.
- Systematic and taxonomic revision of the Pleistocene ground sloth Megatherium (Pseudomegatherium) tarijense (Xenarthra: Megatheriidae). - Journal of Vertebrate Paleontology 29 (4): 1244. - G. De Iuliis, F. O. Pujos & G. Tito - 2009.
- Morphology and Function of the Hyoid Apparatus of Xenarthran Fossils (Mammalia). - Journal of Morphology. Vol: 271. Issue: 9, 1119-1133.- L. M. Perez, N. Toledo, G. De Lullis, M. S. bargo & S. F. Vizcaino - 2010.
- New Pleistocene remains of Megatherium filholi Moreno, 1888 (Mammalia, Xenarthra) from the Pampean Region: Implications for the diversity of Megatheriinae of the Quaternary of South America. - Neues Jahrbuch fr Geologie und Palontologie - Abhandlungen. 289 (3): 339-348. - Federico L. Agnolin, Nicols R. Chimento, Diego Brandoni, Daniel Boh, Denise H. Campo, Mariano Magnussen & Francisco De Cianni - 2018.
- Campo Laborde: A Late Pleistocene giant ground sloth kill and butchering site in the Pampas. - Science Advances. 5 (3): eaau4546. - Gustavo G. Politis, Pablo G. Messineo, Thomas W. Stafford & Emily L. Lindsey - 2019.

Random favourites

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Information about the extinct ground sloth Megatherium and other prehistoric creatures.

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Lyuba: a 40,000-year-old baby woolly mammoth found mummified in Siberia

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Dire wolves, mastodons and short-faced bears, oh my.

Those are just some of the creatures featured in a new exhibit at Victoria's Royal BC Museum called Mammoths: Giants of the Ice Age.

The exhibit includes a 40,000-year-old baby woolly mammoth as its centrepiece, which the museum calls the best-preserved specimen in existence.

The mammoth, on loan from the Shemanovskiy Yamal-Nenets District Museum and Exhibition Complex in Siberia, has been travelling the world since 2010.

The mammoth is named Lyuba, after the wife of the Siberian herder who discovered it, according to Evgeniya Khzyainov, deputy director and curator for the Shemonovskiy Museum.

Khzyainov told Sterling Eyford that the mammoth was about one or two months old when it died by drowning.

"When she died she wasn't damaged by other animals, she was frozen, and when she froze it was [lucky] she wasn't damaged again by animals," said Khzyainov, speaking through an interpreter.

This is the first time that Lyuba will be displayed in Canada - although the exhibit's stop in Toronto featured a replica of the mammoth.

"I know it was very well-received in Toronto - they loved it there," Chris McGarrity, who helped bring the exhibit to Victoria.

"I think it's a fabulous show. It just shows, I think [it] just changes some misconceptions about what these animals were and how they lived, when they lived, where they lived, their evolutionary relationships. That's something that I was really interested in."

McGarrity added another highlight is the exhibit's dire wolf skull.

"Anyone who loves Game of Thrones, like we all do, I think it is really cool for them to see that," he said. "I think there's just something for everyone here ... There's just so much cool material at this exhibit."

The exhibit opens to the public on June 3 and runs until Dec. 31.
With files form CBC Radio One's All Points West and Sterling Eyford To hear the full story, click the audio labelled: 'Best-preserved specimen in existence:' 40,000 year old mammoth coming to Canada for first time To hear the full story, click the audio labelled: 40,000-year-old woolly mammoth Lubya arrives at the Royal BC Museum

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'Best-preserved specimen in existence': 40,000-year-old baby woolly mammoth Lyuba comes to Canada

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A 40,000-year-old wooly mammoth named Lyuba, on loan from a Russian museum, is coming to the Royal BC Museum, and will be seen by the public beginning June 3. The exhibit also features a dire wolf, made famous by Game of Thrones.

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With their enormous, deadly-sharp canines, saber-toothed carnivores are well known to many people as frightening and ferocious predators of the Cenozoic. Surprisingly, there is more than one "saber-toothed cat." The sabertooth morphology has appeared several times during the history of the mammals.

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From the preserved dung of Columbian mammoths found in a Utah cave, a mammoth's diet consisted primarily of grasses, sedges, and rushes. Just 5% included saltbush wood and fruits, cactus fragments, sagebrush wood, water birch, and blue spruce. So, though primarily a grazer, the Columbian mammoth did a bit of browsing as well.

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The AMNH fossil mammal collection is the largest collection of its type in the world. An estimated 400,000 specimens, representing 46 extinct and extant orders, 2808 extinct genera, and 7599 species are housed on seven floors of the Museum's Childs Frick Building. More than half of all the genera of mammals known to science are present in the collection. The cataloged collection contains approximately 2000 type specimens.

Collecting began with the 1877 expedition to the Bridger Basin, Wyoming, led by H.F. Osborn. In 1897, E. D. Cope's vast collection of fossils, which contained many important type specimens, was purchased; this became the core of the paleontological collection. During the AMNH Presidency of H. F. Osborn, and for many decades thereafter, the collection grew through global collecting expeditions led by AMNH vertebrate paleontologists, including W. D. Matthew, Walter Granger, Jacob Wortman, Barnum Brown, Edwin H. Colbert, and George Gaylord Simpson. In 1968, the fossil collection of Childs Frick, consisting mostly of fossil mammals, was donated to the AMNH. More recently, the collections have been further augmented by the active North American and international field programs of Malcolm McKenna, Richard Tedford, Michael Novacek, Jin Meng, John Flynn and their students and collaborators, as well as numerous Divisional Field and Research Associates.

Today, the AMNH collection of fossil mammals is recognized as a national and international resource for research and teaching in paleomammalogy, systematics, and evolutionary biology. Extensive use of the collection is made onsite by staff researchers, visiting scientists, and graduate and postdoctoral students, and additionally through loans of specimens to researchers at other domestic and international institutions. The collection currently receives around 50 professional visitors a year, who average approximately 5 days per visit, and makes about 30 specimen loans to other institutions, averaging 10 specimens per loan.

In recent years, curatorial efforts have focused on upgrades to specimen housing, including the replacement of substandard cabinetry and shelving; making specimen data and digital images available to the wider public via the worldwide web; and improving the standard of environmental monitoring and pest control throughout the collections. The Division has collaborated successfully with the AMNH's Natural Sciences Conservation Lab on a number of projects aimed at improving the standard of preventive conservation in the collection, and has received grant funding for collection improvements from NASA and the National Science Foundation.

Fossil Mammal Contacts

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The AMNH fossil mammal collection is the largest collection of its type in the world. An estimated 400,000 specimens, representing 46 extinct and extant orders, 2808 extinct genera, and 7599 species are housed on seven floors of the Museum's Childs Frick Building.

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Woolly Mammoth general info and references

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Information about Mammuthus primigenius (woolly mammoth) and other prehistoric creatures.

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Smilodon/saber tooth cat general info and references

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Information about the Sabre-toothed cat Smilodon and other prehistoric creatures.

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Pacific Sleeper Sharks are often mistaken as Megalodons in undersea footage!

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A big part of exploring the ocean involves tossing expensive equipment into the sea and hoping it comes back in one piece. Usually, the instruments return-maybe with an extra dent or two.

And every now and then, there's a surprise waiting inside: Like footage of a rarely observed Pacific sleeper shark in a place where none had been seen before.

Sleeper sharks, a group of deep-dwelling, slow-moving fish that includes the Greenland shark, can normally be found in the Northern Pacific and Northern Atlantic oceans, as well as the waters around Antarctica and Tasmania.

But the deep-sea shark researchers filmed popped up around the Solomon Islands east of Papua New Guinea.

"We were freaking out," says Brennan Phillips, a Ph.D. student studying underwater volcanoes at the University of Rhode Island.

Unexpected Cameo

In January 2015, Phillips and colleagues were dropping video cameras, bait, and lights-an instrument package called a drop-cam-into the deep sea off the Solomon Islands as part of their volcano work.

One day, they decided to deploy a drop-cam about 12 miles (20 kilometers) away from an underwater volcano called Kavachi. They wanted to look for "weird" stuff, says Phillips, who was supported by the National Geographic Society/Waitt Grants program.

The instrument ended up 3,074 feet (937 meters) down. When the team retrieved it and downloaded the 7 hours and 45 minutes of footage, they noticed one of the video thumbnails contained a large brown blob. (Watch footage of a Greenland shark blow a researcher's mind.)

The engineer responsible for processing the camera data has a very deliberate way of doing things, says Phillips. He won't skip ahead in the list of video thumbnails, despite pestering from the scientists.

But he broke his rule, Phillips says. "Both of us looked at each other and said, we gotta look at that [thumbnail] right now."

When they opened the file and saw the shark, they started hollering, the volcano researcher says. Phillips knew very little about sharks, and so he sent some screen grabs to experts who could help him identify their unexpected interloper.

A Tricky Identification

The animal seems to be a Pacific sleeper shark, says Marcelo Carvalho, a shark researcher at the University of São Paulo in Brazil.

Usually, experts identify a sleeper shark's species based in part on its location. The three species-the Pacific sleeper, Southern sleeper, and Greenland shark-have distinct ranges, Carvalho explains.

Since the Solomon Islands are fairly close to Australia, Phillips' mystery shark could be the Southern sleeper shark, Carvalho says. However, Southern sleepers tend to be lighter in color than the one in the video.

The mystery shark's color matches that of the Pacific sleeper, as does its gill slits, which are longer than the slits on a Southern sleeper.

Carvalho's best guess? The volcano scientists filmed a Pacific sleeper shark around the Solomon Islands, which would be the southernmost sighting of that species ever recorded.

Continued Mystery

However, "I wouldn't be surprised to find that these three [sleeper shark] species are all the same species," Carvalho says.

The differences between them tend to be slight, and could be the result of geographic variation. It wouldn't be the first time separate species turned out to be the same one, he adds.

To find out requires studying a lot of good quality specimens-no easy task for sleeper sharks. (Read about a rare shark that inspired sea monster myths.)

"They're flabby [and] they get putrid very quickly, so it's hard to preserve them," Carvalho says. Plus, they can grow up to about 21 feet (6.5 meters) long, which makes storing preserved specimens-if you can get them-difficult.

In any case, Phillips is excited to have filmed a live sleeper shark: Video evidence of the mysterious creatures are rare, and most of it is old.

Phillips even got his shark on high definition film: "It's up close and personal."

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Watch: Sleeper Shark Pops Up in Unexpected Place

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A big part of exploring the ocean involves tossing expensive equipment into the sea and hoping it comes back in one piece. Usually, the instruments return-maybe with an extra dent or two. And every now and then, there's a surprise waiting inside: Like footage of a rarely observed Pacific sleeper shark in a place where none had been seen before.

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Megalodon is dead. This shouldn't come as a shock. The fossil record is clear that after about 14 million years of feasting on marine mammals, the 50-foot-long, "mega-toothed" shark exited the evolutionary stage by two and a half million years ago.

But the monstrous shark is too good to let go. If a great white shark is scary, the supersized version is even more thrilling, and despite our ancient fear of sleek, hungry shapes slicing through the water, people really want Carcharocles megalodon to still be alive somewhere in the deep. Peter Benchley toyed with the idea that the great shark might still be out there in JAWS, cryptozoological lore has often spoken of massive sharks, and nature documentaries traditionally state that the prehistoric leviathan is extinct... maybe. Unlike the shark itself, the legend of living megalodon just won't die.

Discovery gave audiences what they wanted. Megalodon had taken up recurring roles in many of their Shark Week programs - including a life-sized " Sharkzilla" solely employed smash stuff - and last year the channel dipped deep into their burbling chum bucket to dredge up Megalodon: The Monster Shark Lives. The program was a shark version of Forrest Gump, with fabricated evidence showing the shark popping up through human history, and had just enough polish to convince many viewers that megalodon is still chomping whales and snaffling up the occasional boat.

The fauxumentary was popular enough that Discovery hastily threw together a sequel for this year's Shark Week carrying the unimaginative title Megalodon: The New Evidence. To quote Marty McFly, "The shark still looks fake." But I don't want to simply despair over Discovery's penchant for trading in on their reputation to peddle attention-grabbing sludge. Bit by bit, we're getting a closer look at megalodon. Paleontologists are continuing to investigate the life of prehistory's most famous shark, including some new, real evidence about when the celebrity selachian slipped into extinction.

University of Alabama paleontologist Dana Ehret is one of the researchers who has been poring over the remains of megalodon. He's helped figure out that the huge carnivore was actually a relatively distant cousin of today's great white shark that should be properly called Carcharocles megalodon, and he's also worked on a trove of teeth that preserve a nearshore nursery for the infants of this imposing species. He's among the scientists who are showing that megalodon doesn't need the reality TV treatment to inspire awe.

Most often, C. megalodon is portrayed as a pumped-up great white. That's because of shared habits. Megalodon were "large macropredatory sharks that ate marine mammals," Ehret says, "and white sharks are a good model for that." The teeth of the extinct shark are distinct from those of any living shark, and the fact that the megatooth lineage split from the great white lineage over 66 million years ago indicates that the megatooth sharks probably had other anatomical differences, but, at least in terms of lifestyle, a huge white shark "is really the closest thing we can imagine megalodon to be," Ehret says.

That megalodon preferred meals of whale and seal fat comes from more than analogy. "We find lots of broken or partial whale ribs that have nice scrape marks or drag marks across them," Ehret says, adding "I've actually taken meg teeth [to compare to the bite marks] and the serrations match up perfectly." Megalodon may not have been above cannibalism, either. "I've seen a tooth with the same scrapes running down the surface of the tooth," Ehret says, although he cautions that this could be a sign of the tooth sliding past another while being shed rather than one shark biting another in the mouth.

Even if they weren't regularly eaten by their own kind, though, megalodon had to cope with competition. Their fossils are found all around the world, Ehret says, in the remnants of coastal environments patrolled by sand tiger sharks, lemon sharks, and other species, including ancient great whites that grew to be 30 feet long. Even at six feet long - as estimate Ehret calculated from a well-preserved vertebra - a newborn megalodon had to cope with similarly-sized neighbors who were chasing after the same food sources.

Striving to find meals may explain a key difference between C. megalodon and modern great whites. From the same vertebra he used to calculate the shark's birth size, Ehret calculated that megalodon grew comparatively faster than great whites. "They just wanted to get a big as they could as fast as they could, and they were a big shark to begin with," Ehret says. Packing on the pounds would have allowed young megalodon to start taking larger prey, and would have prevented them from ending up in the stomachs of their sharp-toothed cousins. "They were trying to get big and get out into more open waters to not have as much competition for resources," Ehret says.

Even with an amped-up growth rate, though, megalodon were never truly able to fully escape early life rivalry. This may have been part of their ultimate demise.

Researchers have traditionally pointed to a cooling global climate as the principal C. megalodon killer, the temperature dip spoiling the shark's warm, nearshore haunts as the water chilled and whales started to migrate towards polar ice. But Ehret suspects that megalodon was able to maintain a high body temperature, much like modern great whites, and would not have been as restricted in range as scientists previously supposed. "I have a bit of a problem saying meg couldn't follow resources to colder waters," Ehret says. Instead, megalodon might have suffered a one-two punch related to growth and food supply.

The evolution and extinction of megalodon tracks the proliferation of prehistoric whales. "You see a peak in whale diversity in the mid-Miocene when megalodon shows up in the fossil record and this decline in diversity in the early-middle Pliocene when meg goes extinct," Ehret says. Without a rich supply of fatty, medium-sized whales, Ehret says, "Meg might've gotten too big for its own good and the food resources weren't there anymore." On top of that, huge great white sharks were still around and vying for the same remaining food sources as juvenile megs. Rather than a victim of temperature, megalodon might have been a victim of "diversity, abundance, and competition," Ehret says.

So when did the last megatoothed shark go extinct? Some sources say that megalodon persisted into the Ice Age, or even into the last 10,000 years. That would make the idea of modern megs seem plausible, but, Ehret says, these late dates are based on faulty evidence. "These teeth get moved, they get tumbled, they get washed down, washed around," Ehret says, and so it's not surprising that dredgers sometimes pluck up megalodon teeth alongside mammoth or mastodon bones. When paleontologists look at in situ megalodon teeth, still in the sediment they were originally buried in, they come up with much older dates.

Robert Boessenecker, a paleontologist at the University of Otago, has led a new study with Ehret and other authorities that pins down the disappearance of megalodon along the California coast. (The research has not yet been published, but soon will be.) The research started with a lucky find.

In late 2007, on the day before Christmas Eve, Boessenecker found a big, bluish green C. megalodon tooth in the Purisima Formation along California's coast. "I got lucky", Boessenecker says, "but I also wondered why we don't find C. megalodon in younger deposits, and why it's so damn rare in latest Miocene/earliest Pliocene deposits." While amateurs and collectors pick up hundreds of megalodon teeth from East Coast sites every year, Boessenecker notes, only about 150 teeth have ever been found in California and the Baja Peninsula.

Comparing the occurrence of the shark along the California coast to records of teeth found elsewhere, Boessenecker and colleagues found that the Carcharocles megalodon did not survive past the end of the Pliocene, about 2.5 million years ago. "No credible records of Pleistocene (or Holocene) C. megalodon exist anywhere," Boessenecker says, "and if we cannot even prove that a giant shark survived past 2-3 million years ago, the case for C. megalodon survival is hopelessly poor." Much of the ocean has yet to be explored, it's true, but it'd be really difficult to miss a 50-foot-long, nearshore shark with a taste for whales. The shark is long gone.

[This clip from Shark Attack 3 is just as educational as Discovery's Megalodon programs.]

Yet the ghost of the shark lives on. Ehret often fields questions directly inspired by the Discovery fiction. "Not only do I see a surge in people asking about megalodon's survival," Ehret says, "it seems that a lot of people that ask really want it to be true." The science Discovery claims to purvey in their fictional programs is getting totally lost. "I really think it does diminish the message [for science] they're putting out there," Ehret says, adding "I think it's all about audience, and it's a little bit like selling out."

Boessenecker has even harsher words for Discovery. The channel still holds a high reputation for factual programming amongst the public, Boessenecker says, which makes "docufiction" like Mermaids and Megalodon especially loathsome. Says Boessenecker:

I find the willful distortion of science by Discovery in favor of entertainment and ratings reprehensible. Discovery may have a short disclaimer in front of the documentary, but it's just lip service; they either know full well that they're being intentionally misleading, or being hopelessly naive in thinking that the public will be able to separate fact from fiction while watching a show advertised as a documentary on a network with a reputation for putting out informative nature documentaries.

For Boessenecker, Discovery's chicanery cuts even deeper because he grew up watching the channel's nature programs and was partly inspired to become a scientist because of them. "And now," Boessenecker says, "that same channel which was so great and educational only two decades ago has dismissed over a century of research in my field with the casual wave of an arm, and for nothing more than ratings."

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Megalodon is dead. This shouldn't come as a shock. The fossil record is clear that after about 14 million years of feasting on marine mammals, the 50-foot-long, "mega-toothed" shark exited the evolutionary stage by two and a half million years ago. But the monstrous shark is too good to let go.

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They are so strange! Interesting to bring up.

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Information about the extinct shark Stethacanthus and thousands of other prehistoric creatures.

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Was the ancient shark Megalodon capable of biting an entire whale's head off? Watch our test chomp to find out if this is even remotely possible.

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Purussaurus

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Information about the giant crocodile Purussaurus and other prehistoric creatures.

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Titanoboa general info with references

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Information about the giant snake Titanoboa and other prehistoric creatures.

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Purussaurus - Miocene vs Deinosuchus - Cretaceous!

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C. Megalodon general info with references

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Information about the giant shark C. megalodon and thousands of other prehistoric creatures.

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By Emily Grebenstein

Catalina Suarez Gomez made the type of discovery that most scientists only dream about - and she did it while interning at the Smithsonian Tropical Research Institute. In 2010 while in Panama, Suarez Gomez was part of a team collecting fossils and geological information along the Panama Canal and in Colombia, including Titanoboa specimens. is the world's largest-known prehistoric snake that scientists estimate slithered around the earth 60 million years ago. Paleontologists had found vertebrae and ribs of a Titanoboa on previous excavations, which allowed them to estimate the massive size of the snake and do inferences on the climate conditions when itwas alive. But in order to get additional information about this animal, they needed more.

While on a field trip with five paleontologists in the Cerrejón coal mine in Colombia, geologist Gersom Garcia alerted Suarez Gomez and biologist Jorge Moreno to additional Titanoboa bones discovered on a walk. As Suarez Gomez describes it, "We took a closer look and there were some different fragments, neither ribs nor vertebrae. My heart started beating so fast. I could not believe what I was seeing. I looked at Jorge's face and he looked at me. 'You know what this is, right?,' he asked. 'YES!,' I told him excitedly. 'These are skull fragments of a snake!,' he said. 'Yes! A huge snake!,' I said. His smile was huge and he said: 'Catalina, we found it. Finally....This is the skull of Titanoboa!'"

"Finding the skull of a snake is like looking for needle in a haystack as the bones are very small and do not hold together as a human skull does," said Carlos Jaramillo, a research biologist at the Smithsonian Tropical Research Institute who oversaw Suarez Gomez's work. "You have to have an acute observation skill. I was very impressed that Catalina was able to find it. The skull provides an unparalleled source of information to understand the anatomy and function of Titanoboa."

Finding Titanoboa's skull fragments allowed scientists to confirm the size and weight of the massive snake - 42 feet long and one ton - and better understand its feeding mechanisms, behavior and the environment in which it lived. With this information, the Smithsonian in association with its research partners, University of Florida and University of Nebraska, was able to create a life-size model of the snake and send it around the country as part of its traveling exhibition series.

Now in her second year at the Universidad Nacional de La Plata in Argentina for a PhD in paleontology, Suarez Gomez considers the Smithsonian a game-changer. "My time at the Smithsonian was one of the best chapters of my life," Suarez Gomez said. "I was not only working on paleontology, but I also could know kind and smart people from many cultures and countries. I had everything I needed: many academic and physical resources, support from the best scientists and kind people around."

"I think the Smithsonian was a breaking point in my life," she continued. "Now, my life is divided in 2 parts: BS (Before Smithsonian) and AS (After Smithsonian). And I think the 'AS' part could be pretty much the best part. Being a former Smithsonian intern has opened many doors for me."

To learn more about internship and fellowship opportunities at the Smithsonian, visit http://www.smithsonianofi.com/.

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By Emily Grebenstein Catalina Suarez Gomez made the type of discovery that most scientists only dream about - and she did it while interning at the Smithsonian Tropical Research Institute. In 2010 while in Panama, Suarez Gomez was part of a team collecting fossils and geological information along the Panama Canal and in Colombia, including Titanoboa specimens.

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Woolly Mammoth (Mammuthus primigenius)  -> Asian Elephant (Elephas maximus)

Ground Sloth (Megatherium) -> Linnaeus' Two-Toed Sloth (Choloepus didactylus)

Saber-Toothed Cat (Smilodon fatalis) -> African Lion (Panthera leo)

Titanoboa cerrejonensis (Titanoboa) -> Boa constrictor

Megalodon (Carcharodon megalodon) -> Great White Shark (Carcharodon carcharias)

Purussaurus (Purussaurus brasiliensis) -> Black Caiman (Melanosuchus niger)

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In light of recent headlines...!

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If you had dreams of riding a woolly mammoth through 2019 after reading headlines this week that 'Wooly mammoth will be back from extinction within two years', you might want to change your plans. It's not going to happen.

Multiple teams of researchers are trying to bring back a woolly mammoth, but it would be disingenuous to imply that the beasts will be roaming the tundra 24 months from now.

What started this furor was an update from one of those teams at the American Association for the Advancement of Science conference in Boston.

"Our aim is to produce a hybrid elephant-mammoth embryo," Harvard's George Church told The Guardian. "Actually, it would be more like an elephant with a number of mammoth traits. We're not there yet, but it could happen in a couple of years."

The key word there is embryo. Church's team-the Woolly Mammoth Revival project-is using CRISPR gene-editing technology to put genetic traits collected from frozen mammoth corpses into Asian elephant DNA.

So far, they've managed to incorporate traits of the mammoth's ears, fat, and hair into elephant DNA. In a few years they hope to make an embryo, but that's a long way from creating a viable embryo. A viable embryo would have to be able to survive long enough to move from a Petri dish to some kind of womb-and then it would have to grow into a healthy calf that the team could successfully deliver and raise.

Artificial gestation is considered the most likely option for any viable embryo, because Asian elephants, the closest living relatives of mammoths, are currently endangered. Church has created an artificial womb capable of gestating a mouse embryo for 10 days but that's a far cry from the 660-day gestation period of an elephant calf.

So while an embryo may indeed be possible by 2019, there's no telling how many years would stretch between that milestone and the actual reintroduction of the woolly mammoth. Researchers have already created embryos of chickens with dinosaur snouts, for example, and those dino-chickens aren't clucking around a co-op. The first attempts to make a living mammoth are many more years away.

And it's important to remember that no one is actually going to bring mammoths back. The manufactured embryo will not be an exact replica of the mammoths that roamed the earth around 4,000 years ago. It will be an elephant manipulated to be more mammoth-like, and it will be something entirely new-a 'mammophant'.

With so many animals going extinct it makes sense that the idea of de-extinction captures public attention. But the easiest way to remedy the loss of an entire species isn't to try to rebuild it from frozen samples or create artificial copies. It's to prevent them from going extinct in the first place.

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No, the woolly mammoth won't actually be resurrected by 2019

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If you had dreams of riding a woolly mammoth in 2019 after reading headlines this week that said; 'Woolly mammoth will be back from extinction within two years', you might want to change your plans. It's not going to happen.

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Transcript for reference

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Megabeasts' Sudden Death

PBS air date: March, 31 2009
Note: This program originally aired under the title "Last Extinction."

NARRATOR: Before the last Ice Age, great mammals ruled the plains of North America: woolly mammoths, saber-tooth cats and other extraordinary animals.

GARY HAYNES (Archeologist): You can't see anything like it today.

NARRATOR: But then, suddenly, they disappeared, and nobody really knows why.

PAUL MAYEWSKI (Glaciologist): It happened so fast.

NARRATOR: Did humans kill them off?

JAMES KING (Geologist): Man probably came to North America as a super-predator.

NARRATOR: Or was their fate more like the one we face today with our climate in crisis?

JAMES KENNETT (Geologist): We need to know how our planet responds to such events.

NARRATOR: Or was it something from outer space?

Now, a new theory has blown the question wide open.

ALLEN WEST (Geologist): It would have been hell on Earth...been a very, very bad day.

NARRATOR: And scientists are fighting over the meaning of startling, new discoveries.

MARK BOSLOUGH (Physicist): You need extraordinary evidence. And I haven't seen that yet.

NARRATOR: NOVA wades into the thick of this controversy in hopes of finding the answer.

JAMES KENNETT: This is art. This, to me, is a Mona Lisa image.

NARRATOR: This is science in action; the stakes are high, the outcome uncertain. Right now, on NOVA, go inside the investigation to solve the mystery of this Last Extinction.

Major funding for NOVA is provided by the following:

Most people feel that ExxonMobil is a company that supplies gasoline in the gas station around the street corner. But we also are working with partners to develop a new energy-saving technology, for future decades, that takes gasoline and converts it into hydrogen onboard a car, with significantly lower greenhouse gas emissions. Our onboard hydrogen system on a fuel-cell car could enable about 80 percent better fuel economy than the cars you and I drive today.

And by Pacific Life: the power to help you succeed; offering insurance annuities and investments.

And David H. Koch. And...

Discover new knowledge: HHMI.

And by the Corporation for Public Broadcasting, and by contributions to your PBS station from viewers like you. Thank you.

NARRATOR: Thirteen-thousand years ago, the Earth's climate was not unlike ours today. But then, suddenly, it changed radically. It was mysteriously thrown back into the Ice Age, and some of the greatest animals that have ever lived vanished: enormous creatures including the woolly mammoth, like a modern elephant, with thick fur and huge tusks; and the saber-toothed cat, a vicious predator, built more like a bear than a lion.

These magnificent animals dominated the Earth for more than 100,000 years, then, like the dinosaurs some 65 million years earlier, disappeared across North America in what is a geologic instant. But unlike the dinosaurs, nobody really knows why.

GARY HAYNES: There was an incredible diversity of animal life, an incredible diversity. You can't see anything like it today.

NARRATOR: Gary Haynes, an archeologist at the University of Nevada, Reno, studies the remains of these animals, and their modern relatives, to try and figure out what happened to this incredible diversity of animal life.

GARY HAYNES: We had several kinds of mammoths, mastodons...we had big predators. We had a lion that was even bigger than the one in Africa today...very much looked like it. We had saber-toothed cats, probably the most memorable animal of all. It looks like a huge cat but it's got these funny fangs. Some of these teeth are big arcing teeth that look just like the saber or dagger blades.

NARRATOR: In all there were between 15 and 35 types of large mammals that went extinct suddenly, including giant sloths, which could be as tall as a giraffe with the girth of an elephant. There were some wonderfully odd creatures, too, like the glyptodont.

GARY HAYNES: Imagine an enormous armadillo with a big armored cover. These are well-defended against predators. You don't see anything like that today; sometimes they probably reached the size of a Volkswagen beetle.

JAMES KENNETT: There was such a rich assemblage of animals. I mean, we go to Africa on safari, well, that is what it was like in North America. All these animals were wandering around, a great diversity of large animals, beautiful animals, and they were lost, in an instant it seems.

NARRATOR: Geologist James Kennett is also fascinated by what killed off these animals, and several of the discoveries throughout his career help illuminate the mystery. It is such a long-standing passion that he, in fact, wrote about it in his very first scientific textbook, at age 11.

JAMES KENNETT: I was going to be a geologist, when I was just 11 years old, and I wrote some books. One's on paleontology. There's a picture of a saber-tooth cat. Here's my rendition of the woolly mammoth. Obviously I must be interested in what knocked these animals off because, having explained what this megatherium is, this giant ground sloth of South America, it says, "Having no protection, the caveman killed it off because of its stupidness."

NARRATOR: But there is nothing stupid, Kennett says, in trying to figure out why these large mammals disappeared, especially today when humans worry about changes in our environment.

JAMES KENNETT: So much happened and so quickly. It was a sad day that these were lost. These were lost and lost so suddenly.

NARRATOR: The extinction of these animals has perplexed scientists for centuries, but today there is a controversial new theory that might just explain it.

Allen West is digging for the evidence. A former geophysicist for the mining and oil industry, West is now using his expertise to investigate this mystery.

ALLEN WEST: Millions and millions and millions of mammoths-mastodons, saber-toothed cats, an American camel, American horse-they all were happily grazing across North America, and they disappeared right at this boundary. They vanished exactly at this point.

NARRATOR: This extinction boundary, plainly visible in this riverbed in southern Arizona near the Mexican border, shows up right under an ominous dark layer of earth, formed by decayed plants and algae. It is called the "black mat."

ALLEN WEST: What I've done here is remove some of the sediment that's above the black mat. And then I'm removing the centimeter or so, the half inch, that's right below the mat, and this is where the mammoths would have walked. So this is the action zone, right there.

The beauty of this mat is this is an extraordinary snapshot into the past. It's so rare in any kind of geologic record to be able to point to a spot and say, "Here's where something happened very suddenly."

NARRATOR: In the past three years, West has dug into his retirement savings, shipping boxes of dirt to colleagues around the world, trying to solve the mystery. West has become his very own FedEx hub of Ice Age dirt.

In a tantalizing early discovery, the team found traces of iridium, one of the rarest elements in the Earth's crust. That discovery meant that they could be onto something really big.

In the late 1970s, a Nobel prize-winner named Luis Alvarez and his son, Walter, also found iridium in geologic layers from 65-million years ago, the time when the dinosaurs got wiped out. It was a stunning find.

ALLEN WEST: While there are amounts of iridium found on the surface of the Earth, they're in tiny quantities. They are, however, in high quantities in meteorites and other cosmic material. So if you find a peak in iridium in a particular layer, then the first suspect is, was there a cosmic event?

NARRATOR: As the evidence mounted, the verdict seemed inescapable. An asteroid from outer space wiped out the dinosaurs. The era of giant beasts that had ruled the Earth for millions of years ended with a bang.

So, do elevated levels of iridium just below the black mat mean that the giant land animals of the Ice Age shared a similar fate?

NARRATOR: Allen West and James Kennett are part of a growing team of scientists that are analyzing this new evidence, and now propose that 12,900 years ago, a comet slammed into the Earth. This cosmic catastrophe would have devastated the great land animals.

It's hard to comprehend the disaster. One of the closest things we have to picturing it is the impact of a nuclear bomb or perhaps several of them.

JAMES KENNETT: If you imagine multiple nuclear explosions occurring over wide areas, generating major pressure waves, flash heat waves, knocking down forests. And this led to wildfires over wide areas, with major destruction of the vegetation. The burning over broad areas of the continent would have destroyed the food resources for many of these animals. And, we suggest, that is why the larger animals, preferentially became extinct.

ALLEN WEST: The larger the animal, the more devastating the effects of this would have been. It would have been hell on Earth...been a very, very bad day.

NARRATOR: Surely such a bad day would leave behind obvious evidence, like this impact crater from 50,000 years ago. But, so far, no crater has been found, and that means the impact team needs to find other compelling proof. And they are now going to the ends of the earth to do so, including here at the Greenland ice sheet.

Paul Mayewski, from the University of Maine, has joined the team and is particularly well-equipped for the job. He is one of the world's foremost glacier experts and has traversed more of Antarctica than anyone else. If there is any evidence sealed away in this magnificent glacier, of a comet that killed off the great animals, Mayewski wants to find it.

The reason he might be able to is that this ancient ice is not only beautiful, but it is also an exquisite frozen library of information about the Earth's history.

PAUL MAYEWSKI: These icebergs have captured within them a remarkable story. Trapped within every single year's worth of snow is an amazing archive of what the environment was like at that time.

NARRATOR: These glaciers are like giant computer hard drives filled with icy data, including ancient microscopic dust.

PAUL MAYEWSKI: The snow itself pulls all of the little dust particles: chemistry that comes out of volcanoes, from forest fires, meteorite impacts.

NARRATOR: Somewhere in the enormous Greenland ice sheet is the very snow and dust that fell when mammoths walked the Earth, and, possibly, the chemical trace evidence of a cosmic impact that wiped them out. But how can you possibly find that specific layer of ice?

During the brief Greenland summer, NOVA brought Paul Mayewski here to take up the challenge. Mayewski brought with him his colleague, Andrei Kurbatov, an expert in analyzing glaciers for microscopic particles.

Mayewski and Kurbatov will be looking for evidence of the impact sealed away in the ice, particularly extra-terrestrial materials like iridium, the clue that helped solve the dinosaur extinction.

The first step, though, is the daunting problem of finding the exact layer of ice from 12,900 years ago in the vast, ancient Greenland ice sheet.

J.P. STEFFENSEN (Glaciologist): We will not move those two dates because we have an eclipse happening.

NARRATOR: And that is why Mayewski is working with J.P. Steffensen, a Danish scientist who knows this glacier as well as anyone in the world.

J.P. STEFFENSEN: If you look here, you can actually see there's this white line between the two black ones. And that is the last layer of this Ice Age ice.

NARRATOR: The layer of ice they are looking for is located between two distinct features caused by Ice Age conditions. Glaciers preserve snow in annual layers, which can be clearly visible, much like tree rings. At the edges of the Greenland ice sheet, these layers get exposed. It's similar to the way layers of Earth are exposed at the black mat.

And there is another parallel. Just as the black mat, in Arizona, appears right where the animals went extinct, here in Greenland, there is a visual marker of this time, as well. Ice from the last Ice Age is gray in color because the arid climate during an ice age erodes the soil, puts a lot of dust into the atmosphere that gets trapped in the ice.

These bands of color, alternating between gray and white, can be clearly seen in this aerial photograph. The ice from the time the mammoths died off should be right between those bands of gray. And each year, during the short Greenland summer, when the glacier is not covered in snow, these color differences are visible on the surface of the ice.

J.P. STEFFENSEN: This dark ice is what we call velvet ice because it has such a velvety, rolling, soft way of running. And then you see in the background...you have much more bumpy and whitish ice comes up. You can see, almost, the transition up there to the hill.

NARRATOR: Steffensen has analyzed this area and found evidence of ice from this mysterious period. Using these color differences, he zeros in on a slope with both colors of ice.

J.P. STEFFENSEN: This is a promising spot. But then again, as you know, Paul, in science, you have to try and hope you are right. But that would be my best guess right now.

NARRATOR: This is science in action and also a very long way to come on a guess, even an educated one.

PAUL MAYEWSKI: I want to make sure to sample the upper part.

NARRATOR: But confirming if this is indeed the right spot will take a sophisticated molecular analysis, which can only be done back in the lab. For now, the job is to collect the samples and hope they're in the right spot.

ANDREI KURBATOV: Just try to use chisel.

NARRATOR: Mayewski and Kurbatov cut a 17-meter trench down the hillside into these exposed layers, from the more recent ice, to older ice, deep into the Ice Age. Samples are taken in 15-centimeter sections. That way any change in the levels of extraterrestrial materials, like iridium, will show up. Many different samples are needed. Specially cleaned bottles are used to collect ice to analyze for the presence of iridium.

PAUL MAYEWSKI: That should do it.

NARRATOR: Other samples are collected to test for oxygen isotopes that can help determine the exact age of the ice. And finally, chunks of ice are taken to see if there are other trapped clues that could be the fingerprint of a cosmic catastrophe.

The stakes are high. Only when these samples are analyzed will Mayewski know if this trip was a waste of time or if it could yield the smoking-gun proof that Earth was slammed by an object from outer space only 12,900 years ago, an object big enough to blast up to 35 kinds of animals into extinction...truly an extraordinary claim.

MARK BOSLOUGH: It's not impossible that you could get an event like that, that recently; it's just extraordinarily improbable. And when you are making an extraordinarily improbable claim, you need extraordinary evidence. And I haven't seen the extraordinary evidence.

NARRATOR: Physicist Mark Boslough analyzes impacts of comets and asteroids. He says one way to evaluate if there was a devastating impact is to calculate the statistical probabilities of it happening. And the odds don't look good.

MARK BOSLOUGH: You have improbability stacked upon improbability. We're talking about something that may happen only once in the entire age of the Earth, and I have a hard time accepting something like that happened that recently.

NARRATOR: Boslough uses some of the Department of Energy's most powerful supercomputers to model the physics of various cosmic impacts and mid-air explosions...

MARK BOSLOUGH: In this simulation I bring in an asteroid-a small asteroid-about 30,000 miles an hour, and it explodes three miles above the surface.

NARRATOR: ...and is able to show clearly their devastating power.

MARK BOSLOUGH: At ground-zero...temperatures as hot as the surface of the Sun, and this vortex is moving at supersonic speeds. So it's like an ultra-white-hot tornado. And this is one of the most extreme events, I think, that could ever happen on the surface of the Earth.

NARRATOR: Boslough says that while an event like this would certainly devastate the environment and the great animals, he thinks there are far simpler explanations.

MARK BOSLOUGH: You know, Ockham's razor? The simplest explanation is probably the best one. And there are other hypothesis that, to me, don't seem as extraordinary.

GARY HAYNES: It seems a little far-fetched. There's a lot of species that did not become extinct, which would be hard to explain. Why weren't they affected if all these other large mammals were? Why weren't the deer and elk and bear affected? Why did they survive?

NARRATOR: Could there be a more down to earth explanation for these mysterious extinctions? Possibly, and to understand them, it is important to investigate what the Earth looked like at that time. And that is the work that Vance Haynes, a legendary archeologist from the University of Arizona, has done.

One day in the 1960s, while walking through this riverbed, Haynes saw bones lodged into the canyon wall. They turned out to be from a mammoth. His ensuing investigation of this site has given us one of the best pictures of life here some 13,000 years ago.

That picture is hard to imagine looking at Arizona today. Instead of sprawling cities, there were valleys full of animals. And instead of the retirees and golfers who flock here, there were other immigrants, the first well-documented humans in North America, the Clovis people.

The Clovis people appear to have arrived in this area just before the black mat is formed. The little information we have about them comes from their beautifully engineered stone tools and spear tips, called Clovis points.

VANCE HAYNES (Archeologist): They are, essentially, functional art. This can be used both as a knife as well as a projectile point. But the basic function of this is for killing game, but yet they took the trouble to get very nice symmetry.

NARRATOR: These sleek, stone weapons were a major advance in hunting technology.

VANCE HAYNES: I think, from seeing their stone technology, they were very sophisticated people. These were probably on a spear that was used for either thrusting or for throwing with a spear thrower. So the idea was, once they penetrate an animal, this would come off, this would stay with the animal, but they would have another one, sort of reload and be ready to go again.

NARRATOR: Haynes' excavations at the black mat proved that the Clovis people hunted the mammoth and other animals here, right up until they disappeared.

VANCE HAYNES: And this is where these animals just came to a sudden end. We've repeatedly dated this level right here at 12,900 calendar years ago. My bottom line is something happened 12,900 years ago that we don't understand.

NARRATOR: Efforts to explain this mystery have led to some very peculiar clues.

The value of this evidence, held under lock and key in the basement archives of the Arizona State Museum, is no B.S. But the evidence itself is exactly that: an ancient piece of poop, giant sloth poop. Yes, you heard that right, giant sloth poop.

JAMES KING: It's not classy science. Working with this stuff in the lab, it smells like you know what.

NARRATOR: Jim King, the former director of the Carnegie Museum of Natural History, says the sloth dung is a goldmine of evidence about how these animals lived and possibly died.

JAMES KING: Fossilized dung is fabulous because in my hand is the evidence of what these animals ate. You see all these fibers, little bits of twigs. Much of this will be Joshua-tree fiber.

NARRATOR: The manure, discovered in a cave, piled five feet high, is high in carbon and therefore makes for perfect radio carbon dating. The last manure in this cave

dates to around 12,900 years ago, the time the black mat appears and not long after the stone artifacts show the arrival of the Clovis people.

Scientists used that coincidence to support a theory that these early hunters were responsible for killing off the great land animals.

JAMES KING: Man probably came to North America at that point as a super-predator with a naí¯ve fauna that had no idea what they were facing. The super-predator had communication, it had weapons, it hunted in groups, it had coordination, it had all the things you would do if you and I were going out to try and hunt big animals.

NARRATOR: More recent history supports this theory. In Mauritius, the arrival of the Dutch doomed the dodo, and in New Zealand, the first settlers killed off the moa. But could this also have happened to these great animals all across North America?

JAMES KENNETT: The data just doesn't support this. It's inconceivable to me.

NARRATOR: Kennett says the idea that primitive humans killed off these powerful animals is absurd, and while it might happen in small island environments, it is impossible to imagine they could wreak such havoc on a continent as vast as North America.

JAMES KENNETT: They didn't have the technology that modern humans have. They didn't have helicopters and machine guns and satellite navigation and so forth. It's always puzzled me. How could they track down that last horse or that last mammoth or that last camel? It just perplexed me. It just didn't make sense.

NARRATOR: If the human overkill theory, as it's called, cannot provide the whole answer, what else can?

NARRATOR: This is not the first expedition that Paul Mayewski has made to these glaciers in search of evidence. In the 1990s Mayewski drilled into the center of the Greenland ice sheet and extracted ice cores going back more than 200,000 years to understand how the world's climate changed. At the time, nobody thought to test for impact markers like iridium, but what they did find was remarkable.

The ice cores proved that the Earth's climate can change extremely rapidly. Sophisticated molecular analysis of the ice can reveal the temperature at the time it formed. The ice from this time, when the animals went extinct, shows a very unusual change: temperatures plummeted.

PAUL MAYEWSKI: It happened so fast. When you think about it, it's unbelievable. It's a complete change in the state of the climate system. It would be the equivalent of going from maybe two or three months of winter in northern New England, let's say, to 11 or 12 months of winter throughout the year.

NARRATOR: In possibly less than two years, the annual temperatures in North America dropped up to 18 degrees Fahrenheit, which may not sound like a lot, but the last time it got that cold in what is present-day Chicago, it was buried under a mile of ice.

Throughout much of the world, climates changed. Some places got colder others dried out, causing more fires. Was this sudden climate change, not the Clovis hunters, what killed off the great land mammals?

ALLEN WEST: There's periods in geologic history where things really go haywire and this was one of those times. We were going through a major climate change. Well, some animals just don't make that change.

NARRATOR: Gary Haynes says that's true, but there were other similar periods of climate change, and these animals survived. Why would this one kill them off? He believes that while climate may have played a role, man was ultimately responsible.

GARY HAYNES: We don't actually like to think of how destructive we are. Even a small amount of killing may have been a decisive factor with some species that were already stressed by climate change, leading to eventual extinction. Humans have always had an impact on their environment.

NARRATOR: The disappearance of the great land mammals is one of the most dramatic and recent extinction events in Earth's history, the last extinction. It also happens to be the time when the Clovis artifacts disappear from the record.

The only history we have is written in the chemistry and archeology that remain behind. And so far these clues have not adequately solved the mystery. Now the new theory of a cosmic impact has blown the question wide open.

The initial finding of iridium at the black mat was a startling discovery. But the levels were much lower than those found at the time of the dinosaur extinction. Because cosmic dust accumulates naturally on the Earth's surface, the low-level iridium findings are not a smoking gun, but were a good tip-off about where to look for more clues. Including the black mat in Arizona, there are at least 31 sites in North America, and six in Europe, where the impact team has collected dirt from the time of the extinctions. That means there is an awful lot of dirt to analyze.

James Kennett and his archeologist son, Douglas, are literally up to their elbows in it.

ALLEN WEST: Look at this, Ted. Here's one, two, three.

NARRATOR: So are Allen West, Jim Wittke, a geologist, and Ted Bunch, who is retired from NASA.

And new technologies, developed since the hunt for the dinosaur killer, have opened up the nano-scale natural world that is embedded in these samples of Earth. What West and team are finding in this ancient dirt is extraordinary.

JIM KING: What in the world is that stuff?

ALLEN WEST: Now, this is a split-open carbon spherule. And we know from the chemistry that these are formed by burning pine trees, burning spruce seeds. This is tree sap, in effect, that's been scorched, burned. But the thing that makes this extremely unusual, in fact the thing that ties it to a cosmic impact, is embedded in the ribs here that you see around.

NARRATOR: One of the most intriguing discoveries, so far, is buried in the spherules. Inside the carbon structures, the impact team has found something that was as thrilling to a scientist as it would be to a young bride, diamonds, nano-scale diamonds to be exact.

ALLEN WEST: All of the rims of each one of these little holes in here is absolutely laced with diamonds. In some cases, 30 percent of that carbon spherule is made up of tiny diamonds.

NARRATOR: These nanodiamonds can be so small that one million of them could be squeezed inside a single grain of sand.

ALLEN WEST: You know, if they could get them out, there's about a trillion dollars worth of these diamonds spread across the United States, so...but it might cost you a trillion to extract them, so...

NARRATOR: All geology jokes aside, it is an important discovery.

TED BUNCH (Retired NASA Scientist): It's like looking at a Hubble image of all the galaxies out in the universe; there are an incredible number of these things.

NARRATOR: Exactly how these nanodiamonds are formed is poorly understood. The team has discovered several different kinds.

Most diamonds found on Earth are cubic, and have a highly symmetrical structure. But one type they are finding, the hexagonal diamond, is not at all common. The only known way to make these is through a high-pressure blast, such as an impact.

TED BUNCH: We see a little hexagonal outline. Woo! Okay, that's cool! These are hexagonal diamonds. Hexagonal diamonds are not found in the Earth's mantel. They do not occur terrestrially. They only in occur in craters, in meteorites, interplanetary dust, et cetera. They are all E.T.

JAMES KENNETT: It's very hard to explain the presence of such numbers of diamonds over such broad areas of the planet, other than from the production from an extraterrestrial impact.

NARRATOR: But is this necessarily so?

MARK BOSLOUGH: I'm still skeptical because they really are invoking a large comet, maybe a couple of miles in diameter. Something that big has enough mass to carry it all the way to the ground, and it would generate a big crater. It would make a big hole in the ground.

NARRATOR: Mark Boslough says that we don't know enough about the formation of nanodiamonds, but if they are the indicator of an impact, where is the crater?

MARK BOSLOUGH: Thirteen-thousand years ago is not very long ago in terms of geologic time. That would be a very young crater. It would be very obvious if something like that existed in North America.

NARRATOR: When the dinosaur-killing asteroid theory was proposed, no one could find a crater either. But then, more than a decade later they did, mostly underwater, and it confirmed the early iridium findings.

NARRATOR: So far, no one has found a crater from the extinction of the large land animals.

Will a crater eventually be found related to this event, or could there be another explanation?

That is the question that Peter Schultz is trying to answer. And he can simulate impacts-on a much safer scale-here, with the hypervelocity gun at the NASA Ames Research Center outside of San Francisco.

PETER SCHULTZ: Okay.

NARRATOR: A small glass pellet is used as the bullet in the gun, and it simulates the cosmic projectile.

The pellet is loaded into this 40-foot long gun and fired into a vacuum chamber to model different possible impact scenarios.

PETER SCHULTZ: This part kills me.

NARRATOR: In this test, Schultz wants to know what would happen if the object from outer space, or the glass bullet, broke into thousands of pieces before hitting the Earth, an idea inspired by the 1994 comet Shoemaker Levy that broke apart before impacting into Jupiter.

PETER SCHULTZ: This could be interesting, especially with the new cameras. I hope we get to see the spray pattern.

Oh, that is so sweet. Let's go see the high-speed cameras.

NARRATOR: High-speed cameras capture the impact and stop the action at up to an astonishing one million frames per second.

PETER SCHULTZ: We have thousands, millions of small fragments slamming into the surface simultaneously. Okay, now, that bright stuff in here, that's the projectile, that's carrying any iridium, any signature of the impact. And after it hit, it would have been blown all over the place and redistributed across the Earth. That is where the gold is. That is the stuff that tells us there was an impact.

NARRATOR: This is the massive crater a single impact would form: pretty obvious. So, what size crater would show up if the same size comet broke up into thousands of smaller objects?

PETER SCHULTZ: We can actually see the individual small craters. And then wind came in and destroyed it. The Earth would recover very easily. Just a little bit of rain and little bit of weather, and you'd lose the evidence.

NARRATOR: A second scenario is that the comet, or at least a major part of it, would have slammed into the Ice Age glacier that covered a large part of North America at that time. That can be simulated here with the impact gun, using a large piece of ice.

PETER SCHULTZ: You have this really intense temperature. The crater just simply forms in the ice. The ice around it cracks, then it simply disappears. Again, you lose the evidence. The ice acted as this flak jacket.

NARRATOR: An impact into the glacier could be another way to explain the lack of a crater, but the burden of proof still lies with the comet theory team, and their strongest evidence, the nanodiamonds, is under attack.

Mark Boslough believes there may be other, far more likely, explanations for the nanodiamonds in the black mat.

For instance, tiny micrometeorites are raining down through our atmosphere at low levels all the time. Was there some way, during all the environmental changes happening at this time, that they became concentrated right under the black mat?

MARK BOSLOUGH: We have this constant rain of micrometeorites. Those contain diamonds. So the question is can you concentrate those diamonds by some mechanism that changes when you have abrupt climate change?

NARRATOR: So now a troubling new question has emerged: when did these nanodiamonds appear? Did they rain in slowly, or appear all at once? Fortunately that is exactly what the glaciers, and their amazing library of information, can answer.

PAUL MAYEWSKI: This is a classic example of how the surface of a glacier can capture an environmental record. You see dust and debris being blown onto the surface of the glacier. More snow comes in, and dust, and effectively gets trapped and then held there for decades, centuries, thousands, and tens of thousands of years, so we have an exact archive of what happened at that time.

NARRATOR: A modern example of this will be smoke from the recent California wildfires. This satellite picture shows how it rises into the atmosphere. Eventually that smoke will make its way to Greenland and be captured in the top layer in the ice sheet. This glacier is, in effect, a safety deposit box with a date recorded of when it was sealed off.

The key question is, can Mayewski find the nanodiamonds or iridium within one narrow layer-equivalent to the layer beneath the black mat from 12,900 years ago-and not above or below? That would prove that this evidence did not rain down gradually over a long period of time.

NARRATOR: Remember how samples were taken across thousands of layers of ice history to see if there is a spike in iridium, carbon spherules or nanodiamonds? Now, back at Mayewski's Climate Change Institute at the University of Maine, the field samples are run through different tests.

The first batch of samples is analyzed to answer the key question of whether or not they succeeded in finding that narrow layer of ice from the time these animals went extinct.

This machine can do that by analyzing the atomic structure of oxygen in the ice, which can reveal the exact temperature when the ice formed.

Mayewski and team have already done this analysis on more than 100,000 years of ice from the Greenland ice cores. So the results from the new sample are compared to this well-established record. It's like comparing temperature fingerprints, and, remarkably, the lab results from this period show a suspected match.

PAUL MAYEWSKI: The likelihood that we would find it was very, very small; it's worse than looking for a needle in a haystack. And suddenly to see on the screen in front of you, it's pretty amazing.

NARRATOR: It looks like Mayewski, Steffenson and Kurbatov found the ice from when these large mammals vanished.

In the lab, they test for the rare element iridium, the finding that helped solve the dinosaur extinction. The results show a spike right at the time when the animals disappear but not a very big one.

PAUL MAYEWSKI: It's not that they're catastrophically higher-they are about three times higher than background-but to have a peak of that level preserved is pretty fascinating stuff.

NARRATOR: This iridium is a tantalizing clue, but, just like at the black mat, there's no smoking gun, because the levels are low. Now it comes down to the nanodiamonds, which are also the hardest to process. Searching through samples from a 17-meter trench for evidence that is a million times smaller than a grain of sand is a very, very painstaking process. That job fell to Allen West.

ALLEN WEST: Pretty hard to work with a 10-micron spherule.

NARRATOR: When the meticulous work is finally done, and West has managed to prepare samples for the transmission electron microscope, NOVA asked Paul Mayewski to join James Kennett and materials scientist Chris Mercer, at U.C. Santa Barbara to have a first look at the evidence.

PAUL MAYEWSKI: That's remarkable-just tons of them all over.

JAMES KENNETT: It is clearly and immediately remarkable.

NARRATOR: The first sample they look at is from the suspected time of the extinctions.

JAMES KENNETT: It consists of a large number of particles.

PAUL MAYEWSKI: ...clearly rained out of the atmosphere.

JAMES KENNETT: This has huge implications. There's no way you are going to get these kinds of particles in the ice sheet unless they are raining out of the atmosphere.

PAUL MAYEWSKI: It's amazing.

JAMES KENNETT: If these indeed are diamonds, then this is a remarkable breakthrough.

NARRATOR: Mercer conducts a test to see if these particles are diamonds. A beam of electrons is shot into them, which casts a series of rings. Each crystal structure scatters the beam in a unique way, forming an identifiable pattern. Immediately, a familiar pattern shows up.

JAMES KENNETT: This is art. This, to me, is a Mona Lisa image, as far as Earth sciences goes.

NARRATOR: These black specks are nanodiamonds in an extraordinary concentration in this one slide.

The test reveals that there are different kinds of diamonds, including hexagonal diamonds, the clearest indicator of an extraterrestrial impact: a diamond believed to have had its atomic structure shaped by massive force.

JAMES KENNETT: I've never seen anything like this before. This is exciting to me, very exciting. I'm looking for cubics on the list and here's hexagonals coming. I'm saying, "Hexagonals in Greenland?" And yet here it is, alive and true in the Greenland ice sheet.

PAUL MAYEWSKI: It's particularly phenomenal because the Greenland ice sheet contains 450,000-plus years of ice, we're trying to find a little layer and bang, the very first slide that we look at has billions of nanodiamonds, the thing that is probably the absolute key to demonstrating that there was a swarm of comets at this time.

JAMES KENNETT: Looking at this kind of material is dramatic.

JAMES KENNETT: Well...

NARRATOR: For James Kennett this moment of discovery becomes overwhelming.

JAMES KENNETT: It's, it's...excuse me.

MAN: It's very exciting?

JAMES KENNETT: Exciting is really not the word. It's an experience you usually don't have much in your scientific career.

Moments of intense discovery are very emotional for scientists. When scientists make discoveries that they think are really important breakthroughs, if you like, "eureka moments," there's an elation. There's an elation, an emotion. These were emotional moments. The hypothesis predicts that the diamonds should have been there and there they were.

NARRATOR: So far, the nanodiamonds have been found only in the layers of ice around the time of the extinctions, a clear indication that they did not rain out of the atmosphere over a long period of time.

PAUL MAYEWSKI: Every single time we find another piece of evidence from the ice sheet, you think to yourself, "My goodness, what else could be possibly be in there?" They capture everything that was going on in the atmosphere. And in this particular case, the evidence is very, very dramatic.

NARRATOR: Each new finding bolsters the theory that a comet wiped out the great land mammals 12,900 years ago.

It is still early in the investigation, and no doubt other explanations will be suggested. Extinctions are very messy things, and many stressors-both climate change and human overkill-were altering the environment. But clearly, this new evidence for a massive impact is changing our understanding of the disappearance of the Ice Age animals of North America.

JAMES KENNETT: It was a sad day for North America, the loss of these animals. The whole landscape would have been so different. In fact, even the human cultural development would've been dramatically different in the last 13,000 years if these animals had, in fact survived.

NARRATOR: On NOVA's Web site, watch video extras, examine a collection of beautiful Clovis artifacts and try your hand at identifying ancient stone tools. Find it on PBS.org.

Major funding for NOVA is provided by the following:

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This NOVA program is available on DVD. To order, visit shoppbs.org or call us at 1-800-PLAYPBS.

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evolution extinction mammoth mega fauna clovis north america

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PBS air date: March, 31 2009 Note: This program originally aired under the title "Last Extinction." NARRATOR: Before the last Ice Age, great mammals ruled the plains of North America: woolly mammoths, saber-tooth cats and other extraordinary animals. GARY HAYNES (Archeologist): You can't see anything like it today.

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NOVA Online | Teachers | Program Overview | Mammoths of the Ice Age | PBS

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Program Overview for the NOVA program Mammoths of the Ice Age: Learn about discoveries of the life and extinction of the woolly mammoth. 1 hr.

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Debate -- Ice Age Extinction

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NOVA | Megabeasts' Sudden Death | The Extinction Debate | PBS

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Follow the heated, decades-long controversy over North America's Ice Age extinctions.