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Theory #1: Diverse groups of organisms evolve from from one or a few common ancestors.
It is obvious that this applies to turtles because they all have one prominent common characteristic, their shell. Since they all have a similarly structured shell, they must have evolved from a common ancestor because it would have given them all that trait. Turtles also share a similar skeletal structure. A common ancestor most likely passed this structure to the many species of turtles we see today.
Theory #2: The mechanism in which evolution occurs by natural selection.
Turtles have definetly evolved through natural selection because traits that common ancestors of turtle had have disappeared for the turtle population. One of these traits is a simple and large skeletal system. Turtles used to be alot bigger, allowing their rib cage to be a lot bigger. Over time, natural selection has chosen smaller turtles with more compact and smaller skeletons and rib cages. As they have evolved, their shells have gotten smaller, forcing their bones and organs to be compact. Their rib cages have alps gotten more complex in order to protect the turtle and its lungs.

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http://biology-forums.com/gallery/33_12_07_11_4_07_15.jpeg

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"Eastern Box Turtle - All Turtles." All Turtles Eastern Box Turtle Comments. N.p., 01 June 2015. Web. 01 May 2016. <http://allturtles.com/eastern-box-turtle/>.

"Box Turtle." Fact Sheet. Smithsonian Institution, n.d. Web. 01 May 2016. <http://nationalzoo.si.edu/Animals/ReptilesAmphibians/Facts/FactSheets/Easternboxturtle.cfm>.

"Red-eared Slider." Facts. Washington Nature Mapping Foundation, n.d. Web. 01 May 2016. <http://naturemappingfoundation.org/natmap/facts/red-eared_slider_712.html>.

"Information About Sea Turtles: Leatherback Sea Turtle." Sea Turtle Conservancy. Sea Turtle Conservancy, 2015. Web. 01 May 2016. <http://conserveturtles.org/seaturtleinformation.php?page=leatherback>.
"Sea Turtle Anatomy « Turtle Time, Inc." Turtle Time Inc. N.p., 2016. Web. 01 May 2016. <http://www.turtletime.org/sea-turtle-facts/sea-turtle-anatomy>.

Heimbuch, Jaymi. "11 Critically Endangered Turtle Species." TreeHugger. N.p., n.d. Web. 01 May 2016. <http://www.treehugger.com/natural-sciences/11-critically-endangered-turtle-species.html>

"World's Oldest Sea Turtle Fossil Discovered." Live Science. Purch, 18 Sept. 2015. Web. 02 June 2016. <http://m.livescience.com/52224-oldest-sea-turtle-fossil.html>.

"Turtle Fossils - Crystalinks." Turtle Fossils - Crystalinks. N.p., n.d. Web. 02 June 2016. <http://www.crystalinks.com/fossilturtles.html>.

"Reproduction." The Bog Turtle Resource. Weebly, n.d. Web. 02 June 2016. <http://bogturtleresource.weebly.com/reproduction.html>.

Bemski, G. "Turtle Hemoglobin: Evidence of a T-state Oxyhemoglobin." Turtle Hemoglobin: Evidence of a T-state Oxyhemoglobin. Relx Group, n.d. Web. 02 June 2016. <http://www.sciencedirect.com/science/article/pii/0014579382801555>.

Weston, Paula. "Turtles." Answers in Genesis. Answers in Genesis, n.d. Web. 02 June 2016. <https://answersingenesis.org/reptiles/turtles/>.

"Turtle." Wikipedia. Wikimedia Foundation, n.d. Web. 02 June 2016. <https://en.wikipedia.org/wiki/Turtle>.

"How Did Turtles Get Their Shells? Oldest Known Turtle Fossil, 220 Million Years Old, Give Clues." ScienceDaily. ScienceDaily, n.d. Web. 02 June 2016. <https://www.sciencedaily.com/releases/2008/11/081126133307.htm>.

"Eastern Box Turtle - The Maryland Zoo in Baltimore." The Maryland Zoo in Baltimore. N.p., n.d. Web. 02 June 2016. <http://www.marylandzoo.org/animals-conservation/reptiles/eastern-box-turtle/>.

"Biogeography of Leatherback Turtles." Biogeography of Leatherback Turtles. N.p., n.d. Web. 02 June 2016. <http://online.sfsu.edu/bholzman/courses/Fall02%20projects/leatherback.htm>.

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Classification-

Red-Eared Slider Turtle

Kingdom
Animalia

Phylum
Chordata

Class
Reptilia

Order
Testudine

Family
Emydidae

Genus
Trachemys

Species
Scripta

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Classification_

Leatherback Sea Turtle

Kingdom
Animalia

Phylum
Chordata

Class
Reptilia

Order
Testudine

Family
Dermochelyidae

Genus
Dermochely

Species
Coriacea

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Classification-

Eastern Box Turtle

Kingdom
Animalia

Phylum
Chordata

Class
Reptilia

Order
Testudine

Family
Emydidae

Genus
Terrapene

Species
T. carolina

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https://en.wikipedia.org/wiki/Turtle

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https://pinterest.com/patriciadallara/turtles

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The leatherback turtle is a sea turtle while the othet two are terrestrial. Seeing as they live in different habitats, their functional and structural characters. Leatherbacks have more leathery shells while the other two have bony shells. This is because the leathery texture allows the sea turtle to swiftly and quicky swim in the water. The bony texure of the bx turtle and slider turtle prtects them from pradators and harsh conditons. While the box and slider turtles have legs, the sea turtle has flippers. The flippers are more advantageous in water because it pushes more water allowing the turtle to go faster. The legs on the box turtle and the slider turtle allow the turtle to stand and walk around easier.

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Geographic Isolation-
Terrestrial turtles and aquatic turtles are separated geographically, so they can’t mate. Species like Eastern Box Turtles live on land and cannot survive living under water. They live in areas like swamps, ponds, and deserts. Aquatic species such as the Green Sea Turtle live in the ocean. If these two organisms were to try to mate, one would probably die in the process because they are meant to live on land or underwater. Since they can’t reproduce together, gene flow stops between them. They have evolved and will continue to evolve to be more and more different from one another.
Reproductive Isolation-
Some organisms are reproductively isolated because they have different numbers of chromosomes. Turtles can have between 20 and 66 chromosomes and if they don’t have the same amount then they cannot mate successfully. This is because their chromosomes wouldn’t be able to join together since there wouldn’t be enough for each chromosome to have a pair. Unless both organisms have the same amount of chromosomes, turtles cannot mate between species. Therefor reproductive isolation does occur in the turtle taxonomic group.

It has impacted these populations because they can no longer mate or attempt to mate. This stops gene flow between populations. When gene flow stops, they will evolve over time and not be able to evolve with the opposite populations because they cant reproduce with them. These populations, because of reproductive and geographic isolation, have become more and more different because of the cease of gene flow.

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It is highly probably that immigration impacts gene flow in turtles, especially sea turtles. Terrestrial turtles have low metabolic rate and have trouble regulating body temperature, so they wont go far from home. They tend to stay in one place unless someone or something forces them to do so. Because of this, terrestrial turtles hibernate during the winter. So gene flow isn’t affected by immigration or emigration. Sea turtles, specifically green sea turtles, migrate. When they migrate, they will immigrate into warm seas full of different species. This means they will be interacting and reproducing with those of other species. Immigration and emigration definitely affects gene flow because sea turtles are constantly moving and interacting/reproducing with other species.

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A small population of ornate box turtles was studied and found to have low genetic diversity due to its small population size. It’s long generation, 22 years, and overlapping generations also contributed to it's low genetic diversity. Their habitat restricted migration, lowering the gene flow in the population. These also resulted in a low genetic drift in the ornate bow turtle population.

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Microevolution-

1. Cretaceous mass extinction- Because of the radiation after the mass extinction of the dinosaurs, aquatic turtles became the mist genetically fit turtles. Turtle species that were aquatic or ambiguous continued to reproduced and spread while terrestrial turtles died out due to radiation.

2. Microevolution decrease- It's been found in many turtle species that there is slow down in the microevolutiuonary rate for turtle mitochondrial DNA (mtDNA). Seeing as turtles have low metabolic rates, there may be a correlation between that and the mtDNA. This may be caused by the oxygen utilization and frequency of DNA damage. This creates low genetic variability in turtles.

3. The shell- Before turtles got their shells, it's highly probably that they lived mainly in the ocean. A fossil shown below shows that a possible turtle ancestor looked exactly as turtles do now, just shell-less. This ancestor evolved to have a shell probably by evolving to have bony, rigid extensions of their back bones and ribs that later grew into a shell. Turtles who had this trait could better protect themselves from harm because the shell was too tough for predators to break. Those without it most likely died off because they didn't have a good form of protection from predators.

Divergent Evolution-

Overall, there are really two kinds of turtles: straight neck and side neck. These types refer to the way turtles retract their heads into their shell. These types are often dependent on diet, habitat and behavior. As turtles evolve, the type of neck they have is becoming more important when classifying turtles. This is because it’s becoming a major characteristic differing between turtle species.

Gradualism-
Order testudines follow gradualism, as they have gradually changed over time. When turtles first became a species, they evolved a shell. They then evolved into separate species and subspecies with different distinguishable characteristics. They evolved to live underwater during the Cretaceous mass extinction radiation and once that ended, came back onto land. This gave us our terrestrial and aquatic turtles. It's obvious that evolution follows gradualism, especially for turtles, because with lots of evidence we can tell that turtles have slowly changed over time.

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Below is a phylogenic tree of turtles throughout prehistoric time periods including the Triassic, cretaceous, and paleogene. The traits expressed were terrestrial, ambiguous, and aquatic. It is obvious that during the beginning of the cretaceous period a drastic change, a mass extinction, in the environment must have occurred to naturally select aquatic turtles as the most genetically fit. During the cretaceous period, the amount of aquatic turtle species grew and there were few to none terrestrial. There was also a period of time between Triassic and cretaceous that most turtle species were ambiguous, meaning they could live on land and in the ocean. As turtles have evolved since then, they have been split into 2 main characteristic, aquatic or terrestrial. This phylogenic tree expressed how that characteristic came to be and why.
http://hoopmanscience.pbworks.com/w/page/65714563/Alex%20Shutter%2029

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Turtles have between 28-66 chromosomes, and chromosome organization and expression can vary between organisms. Their sex-determining mechanisms can also vary, some being determined my chromosomes and some temperature dependent. Between the two organisms, the size, shape and placement of centromere were quite similar. Differences were gene placement, amount of chromosomes, and presence of sex chromosomes.
Below is a link that leads to a karyotype for cryptodiran turtles. It's obvious that they have a lot more chromosomes than we humans do. We have 46 while the cryptodiran turtles have 52. Human chromosomes are overall similar in size, while the cryptodiran turtles chromosomes come in a range of sizes. Human chromosomes, when tightly coiled, are also more distinguishable when it comes to locating pairs, bands and centromeres. The cryptodiran turtles, while it may only be this example, are not as defined. Humans have 2 sex chromosomes, either an XX or XY paring. Cryptodiran turtle’s sex chromosomes are absent, as their sex is temperature-dependent. This means that the temperature in which the organism developed as an embryo determines the sex of the organism.
http://www.ulm.edu/~carr/Carr-etal-1981-Dermatemys-karyotype.pdf

a)      DNA or RNA analysis
Turtle DNA and RNA is constructed the same as all other organisms, using nucleotides that code for proteins. In a phylogenic tree of rRNA nucleotide sequences found in soft shell turtles from Vietnam, it was found that one of the sequences was also found in many specimens in Hung Ky Temple Hanoi, Suoi Hai, Son Tay and Quang Phu , Thanh Hoa. It is thought that these specimens and the soft shell turtles were once from a common ancestor, then separated and forced into allopatric speciation. This proves evolution because the soft shell turtles must have shared a common ancestor with the specimens in order to have the sequence found in their rRNA.
b)      Chromosomal analysis
Turtles have between 28-66 chromosomes, some with and some without sex chromosomes. Those with sex chromosomes have either XX or XY chromosomes. It has been discovered that turtle chromosomes are very similar to those of crocodiles and birds. With this knowledge, we can conclude that they are the closest relatives of turtles. The placement within diapsids in their chromosomes suggests that turtles lost the characteristic of a diapsid skull, much like those of crocodiles, and gained the characteristic of a anapsid skull through evolution. This proves that turtles must have evolved because they share similar chromosomes with crocodiles and birds but have changed to have a different phenotype.
c)      Protein analysis
As turtles age, they grow skutes. These skutes are made out of the protein keratin that  is produced by the turtle. Another protein produced by turtles are Ca-binding proteins. These proteins prove evolution because there must be a common ancestor that passed these proteins onto the many species of turtles we see today.

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All turtles have multiple hemoglobin.

Turtles hemolysates have lower oxygen bonds than mammalian hemolysates

Methemoglobin levels are high, sometimes reaching 90%

universal genetic code, passed on nearly unchanged

Seeing as all turtle have hemoglobins with low oxygen bonds, high methemoglobin levels, and a universal genetic code, they must have had a common ancestor. This ancestor would have passed on these characteristics to the organism we see today, making them evolutionarily related.

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In both of these images of embryonic growth, the pupils are very easy to make out early in development. Both turtles begin to grow a shell very early and show similar signs of shell growth. They both have a bump on the top of their heads that will later conform with the rest of the head. They both also show sign of limbs early in development, stages B for the soft shelled turtle and stage C for the box turtle. These similarities demonstrate relatedness between the organisms because seeing as they look similar as embryos, they must have a common ancestor that gave them these embryonic characteristics.

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http://bogturtleresource.weebly.com/reproduction.html

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htwww.cdbtp://.riken.jp/emo/old-japanese/pubj/pdfj02/tokita_0118.pdf

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These fossils show evidence of evolution because they show how the internal structure has evolved and changed. The bone structure in the fossils is different from the turtles of today’s bone structure. For example, in the first fossil the rib cage is one big bone and a couple of small bone while the rib cage of a more recent turtle is much more complex with many bones varying in size. Another way these fossils show evidence of evolution is the use and structure of shells. In the first fossil, how the shell is structured and how the body is structured inside of it is very different with the fact that the shell had to be a lot bigger to fit the turtles body. Since then, turtles have evolved smaller and tightly compacted internal bones and organs so the turtle could fit into a smaller shell.
All turtle have tightly organized internal bones and organs. This is so their bodies can fit into their shells and still have extra room to fit their head and limbs when sensing danger. Prehistoric turtles however, had much larger bodies. It's obvious that they have evolved to have smaller bodies, seeing as those of the order testudines taxonomic group have a maximum length of 2 meters. Turtles have also evolved to have a more complex but tightly organized internal structure. All turtles have tails, but they have changed in length throughout time. In prehistoric turtles, their tails were a lot longer. Now, most turtles have short tails, normally being around 12 inches long.
Turtles, as well as many species in the animal kingdom, have a sersies of bones in their arms/limbs. This series is known as the one bone, two ones, many little bones, five fellanges. Theese bone are found in humans, bats, whales, and many more other species. These bones are normally found in the limbs of different species, for examples fins, arms and wings. Fins are used to propell water animals through water, wings to allow birds and bats to fly, and arms to stand on or pick up objects. In turtles, this bone series allows sea turtles to propell themselves through water or land turtles to move themsleves around.

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Age of fossil: 120 millions years, Cretaceous
http://blog.hmns.org/2010/06/the-formation-and-preservation-of-the-solnhofen-fossils/

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Age of fossil: Cretaceous
http://www.pbs.org/wgbh/nova/microraptor/foss-02.html

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Age of fossil: Cenozoic
http://www.cmpb.net/en/SMAM2001b.php

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Age of fossil:60 million years old, Jurassic Period
http://www.crystalinks.com/fossilturtles.html

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Age of fossil: Cretaceous Period, between 65.5- 145.5 million years ago
http://m.livescience.com/52224-oldest-sea-turtle-fossil.html

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http://www.chestnuthilllocal.com/2015/01/08/youre-attacked-sons-pet/

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http://www.keywestaquarium.com/category/events/page/3

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http://herpingmichigan.blogspot.com/2011_07_01_archive.html

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Red-Eared Slider Turtle, Trachemys scripta elegans

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Red-Eared Slider Turtle, Trachemys scripta elegans

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Major Characteristics

1. Red-Eared Slider Turtle are found all over the world, including the US, Europe, Mexico and South Africa. They inhabit areas of still warm water, which includes rivers, lakes, swamps and creeks. They required abundant water plants since this is their main food source.

2. Red-Eared Slider turtles have yellow scutes on their brown shells with yellow and black stripes. Their arms, legs and head are green with yellow stripes. They have a red ear marked slightly behind their eye. Red-Eared Slider turtles have a full skeletal system and partially webbed feet.

3. Red-Eared Slider Turtles are almost entirely aquatic and sometimes bathe in the sun to regulate body temperature. They brumate during the winter, which is when they become a lot less active and rarely come to the water surface for air and food. They will become almost motionless and their breathing drops signifagently. Mating occurs between March and July.

How They Evolved
Color- Red-Eared Slider Turtles are brown in color, allowing them to blend into their swamp environments. Their ability to blend into their environment hides them from predators, allowing them to reproduce and spread.

Mating Behaviors

1. Mating occurs between March and July and occurs under water.

2. Before they can mate, they must go through courtship. During courtship, the male swims around the female and vibrates the back of his claws on her face and head. If she is receptive, she sinks to the bottom for mating. If she is not receptive, she might become aggressive toward the male.

3. Females can lay between 2 and 30 eggs depending on factors such as body size.

4. Incubation takes between 60 and 112 days.

5. Females can lay about 3 clutches per season.

6. Red-Eared Slider Turtles use nonrandom selection. During courtship, the female decides if she wants to mate with the male in courtship with her. What characteristics she bases her decision on are not known. If she wants to mate, they sink to the bottom. If not, she will become aggressive with the male.

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Eastern Box Turtle, Terrapene carolina carolina

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Eastern Box Turtle, Terrapene carolina carolina

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Major Characteristics

1. Eastern Box Turtles live in the eastern part of the USA. They are land turtles, but you can sometimes find them wallowing in shallow ponds or streams. When the weather is really hot, they submerge themselves in mud. They are normally found in moist forests or grasslands and never found in rough terrains.

2. The Eastern Box Turtle is known for it's carapace to be high and dome-shaped. The shell is normally brown with yellow, orange and white patterns. The carapace is attached to a hinged plastron that allows the shell to close completely when it feels threatened. Their jaw is slightly hooked and they have slightly webbed feet.

3. The Eastern Box turtle hibernates starting in October or November and end in April. They will borrow 2 feet underground in loose dirt, mud or mammal burrows. When the sense danger, they retract their heads, legs, and arms into their shell and clamp it shut. Eastern Box Turtles normally stay within 750 feet of their home and are often found in groups.

4. They live in groups of 3 or 4 individuals.

How They Evolved
Shell shape- The Eastern Box Turtle’s shell is hinge, allowing it to almost completely shut closed. The shell is also high doomed, fitting the turtles torso and it's limbs. This allows the turtle to retract it's head and limbs into the shell when it senses danger. The possible reason for this variation of shell shape is because is beneficial when trying to protect oneself from danger. Since the shell it's also quite thick, it's hard for predators to crack it open.

Mating Behaviors

1. Eastern box turtles do not leave their home territory, so they will only mate if another turtle of the opposite sex also lives there.

2. Eastern Box Turtle’s mating season begins in spring, carries through summer, and ends in October.

3. Males might mate with more than one female

4. The females lay 3-8 fetrile eggs up to 4 years after mating. They will nest their eggs from May to July. Nests are created by digging a hole in the sand or soil with their hing legs. the eggs are laid and then covered back up. According the temperature and moisture, incubation lasts about 3 months.

5. Females lay several cluthes of eggs each year.

6. Females do not have to mate every year as they are able to store sperm for up to 4 years.

7. Eastern Box Turtles mate randomly because they mate with who ever lives in their home territory. Since they never leave their home, they have to mate with whoever else lives there.

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Leatherback Sea Turtle, Dermochelys coriacea

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Leatherback Sea Turtle, Dermochelys coriacea

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Major Characteristics

1. Leatherbacks are found in open oceans all over the world. They follow jellyfish, seeing as that's their prey, so they are often in deep water during the day and shallow water at night.

2. The Leather Back Sea Turtle is the largest of all turtles, sizing up to 2 meters. They have a teardrop shaped body with a large pair of front flippers and flattened forelimbs. The Leather back Sea Turtle’s shell has a rather leathery skin than a bony texture. Their metabolic rates are high, so they often have higher body temperatures than other turtles

3. Leatherback’s can dive into greta depths of the ocean to prey on jellyfish. They nest 4-7 times per season, with about 10 days between nesting. They will lay about 80 fertilized eggs and 30 small unfertilized eggs.

How They Evolved
Shell type- Instead of a bony shell, the carapace is covered by skin and oily flesh. Since Leather Back Sea Turtles live in the ocean, a leathery, sleek shell allows the turtle to glide quick and easily through the water. A bony shell would create friction and slow the turtle down. By having a leathery sell, the turtle can swim faster to catch prey or escape predators.

Mating Behaviors

1. Mating takes place at sea, seeing as they are sea turtles.

2. Multiple males will reporduce with a single female.

3. Nesting occurs from March to July, females can nest about 5-7 times per nesting season.

4. Nests are dug on beaches in the sand at night. Clutches average 80-85 eggs.

5. Incubation lasts about 65 days.

6. It is not known if Leatherback sea turtles mate randomly or nonrandomly. But if I were to predict which on is used when mating, I’d say randomly. Leatherbacks are endangered and it isn’t very coomon to come across one. So Leatherbacks probably have to mate with whoever they happen to come accross because it's very unlikely that they ever come across another one again.

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-Turtles live in a range of habitats including oceans, desserts, tropical reefs, and beaches. Normally turtles live in dirty places, with many plants for them to eat and topic/sub tropic temperatures. Turtles live in areas in North America, South America, Central America, India, South Africa, and Australia. Turtle fossils have been found in these areas as well.
- During migration, turtles can travel several miles for mating.
-Some turtles, including leatherback and select sea turtles, stay close to the poles.

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-Turtle body temperatures normally are the same temperature of their environment, so they often bask in the sun to raise their temp in order to regulate bodily functions. So most turtles and tortoises cannot be very active in extremely cold or hot temperatures, which means they turn to hibernation.
- For self defense, turtles retract their head and sometimes their legs into their shell. This protects their vulnerable body parts.
- Once year, turtles migrate for mating. They will travel several miles to mate and then find a sandy beach to lay their eggs. They then leave them there and return to the ocean. When the baby turtles are born, they must travel by themselves from the beach to the ocean. If anyone or thing helps them, they will most likely die.

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- Seeing as they are vertebrates, turtle have a backbone. But unlike all other vertebrates, their hip and shoulder bones are inside their ribs.
-They have low metabolic rates.
-They breath from lungs located in their rigid rib cage, which means they must use a different mechanism to breath. Muscles in the leg region inflate the lungs, and then muscles on the surface of the lungs deflate them. Gas exchange occurs in the throat or the cloaca.
-Shells are used as a "calcium bank" to store calcium in. The calcium is used to buffer blood pressure when metabolic acids build up during hibernation. In females, the calcium is used in reproduction.  Calcium is incorporated into egg shells forming around the follicles in the oviducts.
Turtle Skeleton:
http://www.infoturtle.com/turtle-anatomy/

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-Turtles come in all sizes. Their adult size is determined by what kind of turtle they are. They can measure anywhere from 8 cm to 2 meters.
-All turtles have a similar bony shell made up of a carapace (upper shell)formed from costal bones with fused ribs, neural bones with fused thoracic vertebrae, and peripheral bones. In some species, scutes grow on the upper shell. These scutes grow onto of the old ones creating layers. These can be counted to figure out how old the animal is.
- All turtles have a plastron (lower shell) connected to the upper shell made from interclavicle, clavicle, and three to five additional pairs of dermal bones stitched together.
-Most turtles, especially sea turtles, have flippers adapted for swimming. All tortoises have legs that they stand on walk on rather than flippers.
- Turtles have no teeth
-They have long necks to stretch out far or retract into their shells
http://en.wikipedia.org/wiki/Plastral