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1. Eukaryotic
2. Multicellular
3. Heterotrophic
4. Multiple cells with mitochondria
5.  Lack cell walls
6. Food ingested and digested in their internal cavity
7. Food resources are stored as glycogen for fat
8. Nutrition is through food

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A homologous structure found in animalia are hind limbs. Hind limbs originally evolved from Ray-Finned Fish that did not have hind limbs like we think of, but had fins that propelled them through the water. These fins eventually evolved to small limbs in aquatic organisms like the Panderichthys and then to the Tiktaalik which was the first organism to walk on land. From there more modern amphibians evolved such as Tulerpeton. Hind limbs are now on almost all land organisms and allow all of these organisms to walk, like human legs. Hind limbs in modern frogs evolved to be very long and powerful and allow frogs to jump far and high.

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Most live in temperate or tropical region

Extend through a wide variety of habitats

Need both water and land

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Exemplary Example 1:  American Bullfrog

1. Freshwater ponds, lakes, and marshes throughout Nova Scotia, Canada, the U.S., Mexico, and Cuba, and has found its way to Asia, Europe, and South America

2.  Around 8 inches long and 1.5 pounds, green or grey-brown with brown spots, circular eardrums, large mouths, very muscular hind legs

3. Nocturnal predators, will eat anything that they can fit into their mouths, highly territorial, females larger than males

Exemplary Example 2:  Eastern Newt

1. Most of eastern north america from canadian maritime provinces to the great lakes to texas, alabama, georgia, and florida, coniferous and deciduous forests, small bodies of fresh water with mud bottoms, spend most of their time in the water but can survive on land

2. Around 5 inches long, dry, granular, toad-like skin, raised crests between eyes, adult has olive green to yellowish-brown upper parts, small dark spots, yellow belly

3. Adult and larvae forms are aquatic while the intermediate eft form is terrestrial, more active when ground is moist, both nocturnal and diurnal, carnivorous, feed on whatever is most accessible, use vision and chemical cues to locate prey, feed on invertebrates, aquatic reproduction, produces toxins from glands in skin to avoid predation, most live between 3-8 years, but can live up to 15 years

Exemplary Example 3:  Olm

1. spends whole life in a cave, Bosnia, Croatia, France, Italy, Slovenia, underground well-oxygenated fresh water that is between 6-12 degrees C

2. Blind, no pigment in skin, giving it a pasty white appearance, pink hue due to blood capillaries near the skin, translucent - can see outlines of internal organs, short, feeble limbs, elongated head with long snout, scarlet gill tufts on sides of head but develop lungs as an adult, 30 cm long

3. Spends entire life in darkness, can live up to 58 years, chemical cues to find prey, males establish territory during breeding season and fiercely protect it, reach sexual maturity at 7 years

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American Bullfrog -
1. 2-3 month mating season, from late May to July
2. Males have loud breeding calls
3. Fertilization is external
4. Females usually carry 1,000-20,000 eggs but can lay up to 40,000
5. Females are only sexually active for one night

Eastern Newt -
1. Breeding season from late winter to early spring
2. Female is heavy with eggs at this time and is looking for a male
3. Females attracted by male’s spots
4. Male makes fanning motions with his tail and releases pheromones

Olm -
1. Aseasonal breeder,
2. Males will defends territories aggressively during breeding,
3. Male waits for female to come to his territory,
4. Breed every 12 years,
5. Reproductively mature at 14 years,
6. Breeding season is unknown

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American Bullfrog- coloring can range from olive green to grayish brown - if a frog is olive green they most likely live in a grassy or green area and allows them to blend into their environment to invade predators. If the frog is grayish brown it most likely lives in a swampy area.

Eastern Newt - the Eastern Newt is bright orange or red in its terrestrial juvenile stage and becomes a yellowish, greenish, brown in its aquatic adult stage. The reason for this variation is to warn off terrestrial predators with its toxic-looking bright color and it turns this brownish color in the adult stage to blend in with its environment, murky aquatic rivers, like the Mississippi River.

Olm - There is not much variation in the olm, however there is a small subspecies of olms called black olms that have a dark gray or black appearance rather than a translucent white appearance. This subspecies is very small so there  is no great advantage to it other than helping the olm blend in a little bit better however olms already live in very dark underwater caves so there is no great advantage to this variation.

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American Bullfrog - Rana catesbenianus

Tiger Salamander - Ambystoma tigrinum

Eastern Newt - Notophthalmus viridescens

Olm - Proteus anguinus

Wood Frog - Lithobates sylvaticus

Hellbender - Cryptobranchus alleganiensis

Fire Salamander - Salamandra salamandra

Kihansi Spray Toad - Nectophrynoides asperginis

Chinese Giant Salamander - Andrias davidanus

Lesser Siren - Siren intermedia

Mexican Burrowing Toad - Rhinophrynus dorsalis

Northern Spectacled Salamander - Salamandria perspicillata

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Most change from an aquatic larval stage to a terrestrial adult form - called metamorphosis

Most have moist, thin skin with no scales

Feet, if present, lack claws and are often webbed

Most use gills, lungs, and skin in respiration

Eggs lack multicellular membranes or shells - usually laid in water or moist places - fertilized externally

Skin covered in mucus

3-chambered heart

have 5 basic senses - same as humans

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External fertilization

Lay eggs in water

Color discrimination in frog females - respond more favorably to mating calls from frogs that most closely match their own coloration

Reproduce under moonlight - use lunar cycle to coordinate pond gatherings

Eat meat - prey includes insects, slugs, worms, and sometimes small mammals - use their sight, smell, and hearing to track prey

Bury themselves when the weather gets cold

Stay in sun to heat up and go into the water to cool down

Both nocturnal and diurnal

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Eryops megacephalus

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Metoposaurs (Dutuitosaurus ouazzoui)

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Apateon pedestris

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Sclerocephalus haeuseri

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Latonia

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Phlegethontia longissima

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The fossils found show evidence of evolution because all of the ancient amphibians found in the fossils are very large compared to today’s amphibians, which are relatively small. Also, the ancient fossils have very extended faces that look like arrow-heads while today’s amphibians do have extended faces, but not nearly as much as the old ones. Also, the ancient amphibians have very defined teeth that one can see, as in the fifth fossil, but modern amphibians only have vomerine teeth which are not as defined and are only used for holding on to prey rather than chewing or tearing.

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Rana pipiens Stage 1

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Rana pipiens Stage 2

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Rana pipiens Stage 3

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Xenopus laevi

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These pictures taken of the embryological stages of both the Rana pipiens and  the Xenopus laevi  share many similarities to the point where they are extremely difficult to tell apart, which supports the theory of a common ancestor. For example, in stages 5-7 of Rana pipiens and stages 4-7 of the Xenopus laevi, one can see the similarities in the cleavage of the embryo. Both of the embryos in these stages start with a small number of cleavage points and then in stage 7 have lots of different points of cleavage. Also, stage 20 in the Rana pipiens and stage 28 in the Xenopus laevi look almost identical. This is also true in stage 24 of the Rana pipiens and the final stage, stage 39, of the Xenopus laevi.

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Three protein coding genes, Rag-1, Rag-2, and rhodopsin, in 26 different species of anuran amphibians. The chain of nuclear data summed up to 2,616 nucleotides and was complimented by 12s and 16s mitochondrial rRNA genes in order to evaluate these species' evolutionary patterns. The study concluded that modern frogs, called Neobatrachia, all descended from a common evolutionary ancestor.

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Amphibians

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Fish:

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The karyotypes of these different organisms show evidence of evolution through the similarities of the organisms' chromosomes. For example, although they are all related, the Dicamptodon tenebrosus, which is a species of salamanders, is more closely related to fish than the Leiopelma hochstetteri, which is a species of frog, as frogs are known to have evolved later than salamanders. This is shown through the number of chromosomes that the fish species has, which is 22, compared to the other two organisms. The frog species has 11 while the salamander has 14 which is more similar to the fish species. Also, the fish and salamander species' chromosomes share very similar shapes. For example, the first chromosome on both of their karyotypes has many curves while the second is more straight. Also, the final chromosomes in both karyotypes look extremely similar. The frog many of these similarities as well, and it cam be seen that all of these organisms are related, but the salamander and fish are more closely related than the frog due to the overwhelming similarities in the karyotypes. This supports why early amphibians look more like modern day salamanders than frogs as early amphibians evolved from fish.

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Amphibians went through gradual equilibrium as opposed to punctuated equilibrium in that the changes that occurred in them that made them what they are today happened gradually over a long time. The first fish occurred 530 million years ago and Tiktaalik's, the first amphibian, fossil was estimated to be around 375 million years old. That is 155 million years that it took for one organism to even start walking on land from the time of the first fish. This means that the evolution of fins to legs and the development of lungs took a very long time. The evidence provided by organisms such as the Panderichthys, which shows the lengthening of fins, getting more and more like legs and the Acanthostega, which lived underwater but one can clearly see the development of modern-looking legs in their fossils, shows how this development happened gradually.

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Amphibians went through divergent evolution in that they descended from species of fish that developed differences from other species of fish until it formed a completely new group, amphibians. One of these differences was the development of legs that evolved from fins until they were long and strong enough to walk on land. Another difference that separated fish from amphibians is the development of lungs in addition to gills so that amphibians could breathe on land and survive underwater. Differences like these accumulated until amphibians were so different from fish that a whole new group separate from fish was formed

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An example of divergent evolution is the loss of mandibular teeth. Amphibians started out having mandibular teeth and then got split into two different groups, Caecilians and Salamanders. From there, salamanders got split again into salamanders and frogs, based on the loss of mandibular teeth in frogs. This is divergent evolution because a group got split up into two groups based on the loss or retention of a trait, mandibular teeth.

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1. A species of poison dart frogs in Peru called Ranitomeya imitator can imitate other frog species and is splitting into two different species because of this. One morph of this species, called “striped”, acquires Ranitomeya variabilis traits such as black and yellow stripes and aquatic marbles legs while the other morph, called Varadero acquires traits from R. fantastica such as an orange head, black spots, and blue legs.
2. Microevolution is also occurring in the form of a threat to genetic variation due to pollution. Pollution threatens one third of amphibians with severe genetic erosion which could lead to extinction in the future. Genetic erosion is having an effect on fitness, the ability to survive and produce offspring, environmental plasticity, or changes in behavior, morphology, or physiology because of an adaptation to a new environment, co-tolerance mechanisms, trade-off mechanisms, and tolerance to pathogens.
3. There is also a form of human-induced microevolution happening in the near future to save amphibians in the Cascade Mountains. Amphibians in this area are suffering from a variety of things including the melting of glaciers and the drying of the climate, but are also being severely impacted by diseases caused by chytrid fungus. Scientists are currently developing a form of microevolution to use yellow-legged frogs from the Sierras that are resistant to the disease as a way to make amphibians from the Cascade Mountains resistant to the disease.

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Descent with modification is present in amphibians in that amphibians originally descended from fully aquatic fish and then over time, there was a benefit in being able to survive on water and on land, so once an organism was able to walk on land, Tiktaalik, it had an advantage and was able to survive and reproduce better than other organisms. Because this organism was able to survive and reproduce better, it passed down its traits to its offspring and they had a better chance of surviving and reproducing so they passed these traits down to their offspring. This kept happening because there was an advantage in having this trait and now we have amphibians that are thriving because of their ability to survive in water and on land.

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Amphibians have undergone disruptive natural selection because for almost every organism in the taxonomic group, there are two extreme forms of a trait that provide more of an advantage than the original trait. For example, in the Eastern Newt, the two extremes are a very dark brown/green color that provides an advantage of camouflage or a very bright orange color that makes the newts look poisonous so other organisms will not eat them.

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The first species in this karyotype is a salamander and the second species is a frog. The salamander karyotype has 14 chromosomes while the frog karyotype has 11 chromosomes. In addition, the frog species’ chromosomes are more misshapen than those of salamander, which are more uniformly shaped. However, the first 4 or 5 chromosomes in the frog look very similar to those of the first 4 or 5 of the salamander. Also, the last 5 or 6 chromosomes of the frog look very similar to the last 5 or 6 chromosomes of the salamander.

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This phylogenetic tree shows the progression of mandibular teeth over time. At first, all amphibians had these teeth and then with the evolution of Anura, or frogs, these teeth became absent, while Caudata, or salamanders, and Gymnophiona, or Caecilians, remained with the mandibular teeth. However, a species of Anura called Gastrotheca guentheri has shown re-evolution of mandibular teeth.

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Many species, including the species Pelodryadine hylids, were affected by the fragmentation of former continents such as Pangea, Laurasia, and Gondwana. These amphibians moved to one part of the world to another with these splits. As in Pelodryadine hylids, they can be found in Australia or New Guinea but are deeply rooted to a group of amphibians that are only from South America.

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http://www.marylandzoo.org/assets/Eastern-Newt-a-877x265.jpg

https://3c1703fe8d.site.internapcdn.net/newman/gfx/news/protee.jpg

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https://ecologicablog.files.wordpress.com/2012/08/amphibia-phylogeny.png

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http://www.earthhistory.org.uk/wp-content/KvD_Padian_s040.jpg

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http://www.jouefct.com/wp-content/uploads/2016/01/Frog-Internal-Anatomy-The-frog-is-among-a-handful-of-small-animal-species-that-serve-as-laboratory-specimens-for-hands-on-learning.gif

http://www.animalspot.net/wp-content/uploads/2013/02/Salamander-Anatomy.jpg

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