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I often see pictures of turtles riding alligators, I even saw that in a zoo once, but why do they do that?
Is it some sort of camouflage technique for the turtles? And why doesn't the alligator get it off?
turtles will crawl onto anything to get out of the water and bask, fallen logs are common and they likely cannot tell the difference between a still alligator and a log. It might also be possible that the turtles do know what the gator is and are hoping to tag along and pick up scraps after it strikes.
I image that for the gators thrashing around to dislodge the turtle has to high a risk of scaring off prey so they just put up with it.
Alligator Snapping Turtle Facts
The alligator snapping turtle (Macrochelys temminckii) is a large freshwater turtle native to the United States. The species is named in honor of Dutch zoologist Coenraad Jacob Temminck. The turtle gets its common name from the ridges on its shell that resemble the rough skin of an alligator.
Fast Facts: Alligator Snapping Turtle
- Scientific Name: Macrochelys temminckii
- Distinguishing Features: Large turtle with strong jaws and a ridged shell resembling alligator skin
- Average Size: 8.4 to 80 kg (19 to 176 lb) males larger than females
- Diet: Primarily carnivorous
- Average Life Span: 20 to 70 years
- Habitat: Midwest to Southeast United States
- Conservation Status: Vulnerable
- Kingdom: Animalia
- Phylum: Chordata
- Class: Reptilia
- Order: Testudines
- Family: Chelydridae
- Fun Fact: Although not aggressive, the turtle can deliver a bite powerful enough to amputate fingers.
Alligator snapping turtles are sometimes described as dinosaur-like because of their spiky shells and primitive-looking faces. They have three pointed ridges along their shells that run from head to tail. Unlike all other species of snapping turtle, this one has eyes on the sides of its head.
The alligator snapping turtle is the largest species of freshwater turtle. Males typically weigh between 155 and 175 pounds (70 and 80 kilograms). It is said that a 400-pound (180-kilogram) alligator snapping turtle was caught in Kansas in 1937, but there isn’t sufficient evidence to confirm the claim.
Alligator snapping turtles are found exclusively in the United States, from northern Florida to eastern Texas and as far north as Iowa. They are almost exclusively aquatic, and tend to stay submerged and motionless for so long that algae begins to grow on their shells. They can go 50 minutes before needing to surface for a gulp of air. Except for egg-laying females, these turtles almost never come on land. River systems, lakes, and wetland comprise their preferred habitats.
Their specially adapted tongue allows them to catch prey with little work—a lure-like projection of the tongue attracts curious fish that swim right into the turtle’s mouth. To attract an unsuspecting victim, this turtle will lay on the bottom of the riverbed and open his jaws to reveal what looks like a delicious bright red wriggling worm, luring prey by fiendishly twitching this appendage back and forth. A fish that gets duped by the turtle’s tongue will swim right into the range of the hungry predator’s jaws.
They can also actively search for prey by tasting chemicals in the water that are indicative of a particular species. This way, even when their prey is hiding in the sediment, they can still sense them.
These solitary reptiles spend much of their time in the water—even capable of holding their breath for 40 to 50 minutes. They venture onto land to nest with females. Correlated with a solitary lifestyle, there is little structure and no parental care to their young.
Adults mate in the spring and females lay eggs two months later. The eggs hatch after 100 to 140 days. The incubation temperature of the nest determines the gender of the offspring—females develop in warmer temperatures and males develop in cooler temperatures. The newly hatched turtles are similar to the adults in appearance. Eggs and juveniles are consumed by fish, raccoons, and birds, but the only predator of fully grown adults is humans. Reproductive maturity is reached at 11 to 13 years. The turtle’s typical lifespan in the wild is between 11 and 45 years, but captive alligator snapping turtles have lived to 70 years of age.
Alligator snapping turtles are declining due to habitat degradation and overharvesting for their meat. They are not an endangered species, but some states have imposed bans on collecting them from the wild.
Some myths claim that alligator snapping turtles are known to attack people, but this isn’t the case. But with a bite force of 1,000 pounds, their powerful jaws can snap through bone—so they should never be handled in the wild.
Common misconceptions about alligators
Alligator skin is not bullet-proof
Contrary to the common myth, alligator skin (and also crocodile skin) is not bulletproof.
They do not eat their babies
Neither alligators nor crocodiles eat their babies. No crocodilian do that. Evon Hekkala, the principal investigator at Fordham University’s Hekkala Lab and a research associate at the American Museum of Natural History, says “A long time ago, people would observe the crocodiles and alligators digging up nests and having hatchlings in their mouths, and they would think that they were eating them.” In fact, they were taking their babies to the water.
A healthy adult can easily outrun an alligator
It is a myth that an alligator can outrun a human. Alligators top out at a speed of around 11 miles per hour (18 kph) on land when they “belly run”, and for a very short distance. It can’t maintain that speed for very long. They usually go much slower than that. While walking on their legs, which is called the “high walk”, their top speed is only 5 km/h (3 mph). So, an average healthy adult human could easily outrun an alligator, zigzagging or not.
Alligator snapping turtle
Alligator snapping turtles are native to the southern United States. They are found in rivers and streams that feed into the Gulf of Mexico. Their range stretches from Iowa, west into Texas, and east into Georgia and northern Florida. Genetic analyses revealed that there are three genetically distinct subpopulations of alligator snapping turtles, residing in the greater Mississippi River watershed, the Gulf coastal rivers east of the Mississippi River and the Suwannee River drainage system in Florida.
Alligator snapping turtles are predominantly aquatic, spending most of their time in the water. They can stay submerged for 40 to 50 minutes before needing to surface for air. They are only found in freshwater systems and tend to prefer the deeper beds of large rivers, canals and lakes. However, juveniles may be found in smaller streams.
Alligator snapping turtles are primarily carnivorous. They eat fish and other aquatic animals, but have also been known to eat small mammals and some vegetation. These turtles are most active at night and will scavenge or hunt for food. When hunting, these ambush predators stay motionless in the water and reveal the worm-like appendage on their tongues to lure unsuspecting prey.
Alligator snapping turtles reach sexual maturity between 11 and 13 years. They tend to mate in early spring. Because they are typically solitary, they may have to travel to find a mate. The male mounts the back of the female and holds her shell with all four feet during copulation. Females then travel inland to dig nests in the sand. They generally lay only one clutch per year, or possibly one every other year. Clutch sizes range from 10 to 60, and the eggs incubate for about 100 days.
This species was assessed in 1996 by the IUCN Red List and is listed as vulnerable. It is also protected under a listing in the CITES Appendix III. In the United States, protections for the alligator snapping turtle vary from state to state, ranging from prohibitions on collecting wild individuals for commercial use and personal use to restrictions on commercial use. It is illegal to capture wild alligator snapping turtles in Arkansas, Florida, Georgia, Indiana, Missouri and Tennessee, and a permit is required in Alabama, Illinois, Kansas, Louisiana, Oklahoma and Texas.
The largest threat facing alligator snapping turtles has been uncontrolled wild harvesting for their meat, unique shells and to sell as exotic pets. Because they are large and easy to capture, the turtles' meat is harvested for consumption in domestic and international markets. It was most popular in the 1970s and 1980s for use in canned soup.
There are three, genetically distinct subpopulations of alligator snapping turtles. Taking individuals from one or more of these populations could lead to local extirpation, which reduces the overall genetic variability that protects populations from disease outbreaks. Losing that genetic diversity would also make it more difficult to find founders for populations in breeding programs designed for species conservation. Consumers making informed, responsible choices about exotic meats and agricultural products can lessen the pressure on these animals.
Agriculture in areas that formerly hosted bottomland hardwood forest and streams also impacts alligator snapping turtles. The conversion of these lands into agricultural fields and commercial developments replaces suitable habitat. Riverside developments usurp the turtles by removing nesting sites. Activities in these areas lead to the degradation of aquatic habitats downstream, because agrochemicals, pesticides, silts and other dissolved solids reach the water and are carried downstream. These added inputs alter the pH, turbidity and flow of water in sites well beyond the reaches of human settlements.
Programs in Arkansas and the Lower Mississippi Valley that establish and protect waterfowl habitat have countered some of these impacts by maintaining suitable habitat for other freshwater species like the alligator snapping turtle. These protections, in turn, help maintain the overall health of that ecosystem.
Alligator snapping turtles are apex predators and, because of their position at the top of the food web, play an important role in the ecosystems they inhabit. They act as a check on the populations of the species they consume, such as regulating the prevalence of certain fish. As scavengers, they provide an additional service by removing the remains of deceased animals.
The Alligator Has a Permanently Erect, Bungee Penis
In the video above, Brandon Moore from Louisiana Tech University is dissecting a freshly dead male alligator. You’re looking at the creature’s underside, near its hip area. As the sequence begins, Moore’s scalpel touches the alligator’s pelvic nerve. The metal makes the nerve fire and… well… just watch the video.
That’s the alligator’s penis—ten centimetres long, ghostly white, and surprisingly quick-moving. It flips out in an instant and just hangs there for a few seconds to greet a startled Moore, before twanging back inside just as quickly. I love that Moore back-steps and freezes. There’s no audio. I wish there was audio.
The video was a revelation to Diane Kelly from the University of Massachusetts, and the key to interpreting the utterly bizarre penis of the American alligator. Here are the highlights: it’s permanently erect it shoots out like toothpaste from a tube and it bounces back because it basically has a rubber band attached to it. “It is really weird,” says Kelly. “Really weird.”
That’s not something she’d say lightly. Animal penises are her speciality. She has studied and dissected the male organs of mammals and turtles to better understand their anatomy and their evolutionary history. Meanwhile, her close colleague Patricia Brennan—“the other penis lady”—had done a lot of work on birds, snakes and lizards (remember the infamous duck penis video?). The crocodilians—crocodiles, alligators and their kin—seemed like the obvious group to target next.
Here’s what we knew about their penises before Kelly started. The males have a single large phallus stashed within the cloaca. That’s the joint opening you can see in the video above, which also gives way to the urinary and digestive tracts. Sperm travels along a deep groove running the length of the penis, which is surrounded by dense tissue. Okay, but how does a crocodilian inflate its penis or eject it from the cloaca?
To find out, Kelly needed to get her hands on some crocodilians. Fortunately, she didn’t have to work with living ones. In September, she headed down to the Rockerfeller Wildlife Refuge in Louisiana, which has an annual cull to control the local population of American alligators. They let her work with four of the animals that had been shot, including a huge four-metre-long bull. “It was really scary, even though it was dead!” says Kelly.
Through dissection, she discovered that the alligator’s penis doesn’t inflate at all. It’s permanently erect. The whole structure is filled with dense layers of a stiff protein called collagen. Even the central bit, where blood would normally flow down, is just collagen, collagen and more collagen.
That’s bizarre. Whenever a reptile, bird or mammal has a penis (and some don’t), it always inflates in some way. Maybe blood pumps into it, as in humans, other mammals, and turtles. Maybe it explosively turns inside-out like in ducks and some lizards or snakes. Either way, some shape-changing occurs. But not in alligators—when Kelly tried to artificially inflate the penis by pumping saline, it didn’t change in either length or diameter.
So, if the penis doesn’t inflate, how does the male alligator extrude it from the cloaca? Muscles would be the obvious answer, but continuing the theme of “really weird”, the penis has no muscles attached to it. It’s almost free-floating. One pair of muscles—the levator cloacae—cradle the penis like a sling, but doesn’t actually connect.
This stumped Kelly until she saw Moore’s video. She now thinks that when the levator cloacae contract, they force the penis out by squeezing the cloacal chamber. “This squishes the whole penis and pops it out of the vent,” she says. Indeed, when Kelly yanked on the levator cloacae by hand, the penis of her dead alligator leapt into the outside world.
I said the penis is almost free-floating. It’s got a tendon that connects to its middle, which helps to swivel it forwards when it pops out. Its base is also attached to the hip bone by a pair of large ligaments, that are “the consistency of the big rubber bands the post office uses,” says Kelly. When the penis comes out, these rubber bands are stretched. As soon as the levator cloacae relax, the elastic ligaments yank the penis back in.
Mystery of Alligator Movement Solved
Instead of swishing fins, feet or flippers, alligators surprisingly move their lungs around inside their body to dive, surface and roll in water.
This newly discovered strategy may be one that many animals have been employing for millennia to maneuver and avoid creating ripples in the water — helping them sneak toward prey or away from predators.
Up until now, it was a mystery as to how gators "manage to maneuver so gracefully without the fins and flippers used by fish, seals and other adept swimmers," said researcher C.G. Farmer, a biologist at the University of Utah at Salt Lake City.
The researchers noticed alligators seemed to have a lot of muscles devoted to breathing. "They really didn't need all those muscles for breathing, so we wanted to see what else they might be doing with them," said researcher T.J. Uriona, also a University of Utah biologist.
Farmer and Uriona investigated five American alligators (Alligator mississippiensis), each 2 years old, from Louisiana's Rockefeller Wildlife Refuge. The gators were just 15 to 20 inches long. In comparison, adults can reach 15 feet.
Electrodes were implanted on sets of muscles in the alligators so their activity could be monitored while the reptiles maneuvered in warm water in 100-gallon tanks. The researchers also duct-taped weights made of buckshot pellets under the reptiles' jaws or at the base of their tails that totaled about one-fortieth of each gator's weight, providing a bit of added stress to help the electrodes better detect how the muscles worked.
"Gators are surprisingly easy to work with — they're not very aggressive animals, and tend only to bite out of self-defense," Uriona said.
Farmer and Uriona focused on special muscles the alligators used to manipulate the position of their lungs. Until now, it was believed these muscles evolved to help gators breathe and run at the same time, Uriona said.
"It may be that instead of these muscles arising for breathing, they arose for moving around in the water and later were co-opted for breathing," he explained.
The lungs act as flotation airbags. By moving the lungs around, the muscles alter the center of buoyancy of the alligators. The researchers found moving the lungs toward the tail helped the gators dive toward the head helped them surface and toward one side or the other helped them roll sideways. The tail also helped the reptiles roll.
Scientists had assumed that alligators maneuvered in water simply by controlling how much air they breathed in. "If they wanted to sink, they'd just take in less air if they wanted to surface, they'd take a big breath," Uriona said. "Sometimes things get overlooked."
The crocodilian ancestors of alligators — slender, cat-sized animals that initially lived only on land — may have developed these muscles when they became amphibious about 145 million years ago. By shifting their lungs around, these reptiles could then silently maneuver without disturbing the water.
"This is probably really important while they are trying to sneak up on an animal but don't want to create ripples," Uriona said. Sneaky maneuvering could also help the gators from getting eaten themselves.
Similar muscles are found in crocodiles, turtles, African clawed frogs, certain salamanders and manatees. The researchers are now investigating whether these animals use their lungs to orient in the water like alligators do.
"People typically think of lungs as just sacs of air, as a way of keeping in oxygen, but our findings show animals can use that air when in the water to manipulate their position in space," Uriona told LiveScience.
Uriona and Farmer detailed their findings online March 14 in the Journal of Experimental Biology.
Rise from water Edit
Reptiles first arose from amphibians in the swamps of the late Carboniferous(Early Pennsylvanian - Bashkirian ). Increasing evolutionary pressure and the vast untouched niches of the land powered the evolutionary changes in amphibians to gradually become more and more land-based. Environmental selection propelled the development of certain traits, such as a stronger skeletal structure, muscles, and more protective coating (scales) became more favorable the basic foundation of reptiles were founded. The evolution of lungs and legs are the main transitional steps towards reptiles, but the development of hard-shelled external eggs replacing the amphibious water bound eggs is the defining feature of the class Reptilia and is what allowed these amphibians to fully leave water. Another major difference from amphibians is the increased brain size, more specifically, the enlarged cerebrum and cerebellum. Although their brain size is small when compared to birds and mammals, these enhancements prove vital in hunting strategies of reptiles. The increased size of these two regions of the brain allowed for improved motor skills and an increase in sensory development.
Early reptiles Edit
The origin of the reptiles lies about 320–310 million years ago, in the swamps of the late Carboniferous period, when the first reptiles evolved from advanced reptiliomorph labyrinthodonts.  The oldest known animal that may have been an amniote, a reptile rather than an amphibian, is Casineria   (though it has also been argued to be a temnospondyl amphibian). 
A series of footprints from the fossil strata of Nova Scotia, dated to 315 million years, show typical reptilian toes and imprints of scales.  The tracks are attributed to Hylonomus, the oldest unquestionable reptile known.  It was a small, lizard-like animal, about 20 to 30 cm (8–12 in) long, with numerous sharp teeth indicating an insectivorous diet. 
Other examples include Westlothiana (sometimes considered a reptiliomorph amphibian rather than a true amniote)  and Paleothyris, both of similar build and presumably similar habit. One of the best known early reptiles is Mesosaurus, a genus from the Early Permian that had returned to water, feeding on fish.
The earliest reptiles were largely overshadowed by bigger labyrinthodont amphibians, such as Cochleosaurus, and remained a small, inconspicuous part of the fauna until after the small ice age at the end of the Carboniferous.
Anapsids, synapsids, diapsids and sauropsids Edit
It was traditionally assumed that first reptiles were anapsids, having a solid skull with holes only for the nose, eyes, spinal cord, etc.  the discoveries of synapsid-like openings in the skull roof of the skulls of several members of Parareptilia, including lanthanosuchoids, millerettids, bolosaurids, some nycteroleterids, some procolophonoids and at least some mesosaurs    made it more ambiguous and it is currently uncertain whether the ancestral reptile had an anapsid-like or synapsid-like skull.  Very soon after the first reptiles appeared, they split into two branches.  One branch, Synapsida (including modern mammals), had one opening in the skull roof behind each eye. The other branch, Sauropsida, is itself divided into two main groups. One of them, the aforementioned Parareptilia, contained taxa with anapsid-like skull, as well as taxa with one opening behind each eye (see above). Members of the other group, Diapsida, possessed a hole in their skulls behind each eye, along with a second hole located higher on the skull. The function of the holes in both synapsids and diapsids was to lighten the skull and give room for the jaw muscles to move, allowing for a more powerful bite. 
Turtles have been traditionally believed to be surviving anapsids, on the basis of their skull structure.  The rationale for this classification was disputed, with some arguing that turtles are diapsids that reverted to this primitive state in order to improve their armor (see Parareptilia).  Later morphological phylogenetic studies with this in mind placed turtles firmly within Diapsida.  All molecular studies have strongly upheld the placement of turtles within diapsids, most commonly as a sister group to extant archosaurs.    
Mammalian evolution Edit
A basic cladogram of the origin of mammals. Important developments in the transition from reptile to mammal were the evolution of warm-bloodedness, of molar occlusion, of the three-ossicle middle ear, of hair, and of mammary glands. By the end of the Triassic, there were many species that looked like modern mammals and, by the Middle Jurassic, the lineages leading to the three extant mammal groups — the monotremes, the marsupials, and the placentals — had diverged.
Permian reptiles Edit
Near the end of the Carboniferous, while the terrestrial reptiliomorph labyrinthodonts were still present, the synapsids evolved the first fully terrestrial large vertebrates, the pelycosaurs such as Edaphosaurus. In the mid-Permian period, the climate turned drier, resulting in a change of fauna: The primitive pelycosaurs were replaced by the more advanced therapsids. 
The anapsid reptiles, whose massive skull roofs had no postorbital holes, continued and flourished throughout the Permian. The pareiasaurs reached giant proportions in the late Permian, eventually disappearing at the close of the period. 
Late in the period, the diapsid reptiles split into two main lineages, the archosaurs (ancestors of crocodiles and dinosaurs) and the lepidosaurs (predecessors of modern tuataras, lizards, and snakes). Both groups remained lizard-like and relatively small and inconspicuous during the Permian.
The Mesozoic era, the "Age of Reptiles" Edit
The close of the Permian saw the greatest mass extinction known (see the Permian–Triassic extinction event). Most of the earlier anapsid/synapsid megafauna disappeared, being replaced by the archosauromorph diapsids. The archosaurs were characterized by elongated hind legs and an erect pose, the early forms looking somewhat like long-legged crocodiles. The archosaurs became the dominant group during the Triassic period, developing into the well-known dinosaurs and pterosaurs, as well as the pseudosuchians. The Mesozoic is often called the "Age of Reptiles", a phrase coined by the early 19th-century paleontologist Gideon Mantell who recognized the dinosaurs and the ancestors of the crocodilians as the dominant land vertebrates. Some of the dinosaurs were the largest land animals ever to have lived while some of the smaller theropods gave rise to the first birds. 
The sister group to Archosauromorpha is Lepidosauromorpha, containing squamates and rhynchocephalians, as well as their fossil relatives. Lepidosauromorpha contained at least one major group of the Mesozoic sea reptiles: the mosasaurs, which emerged during the Cretaceous period. The phylogenetic placement of other main groups of fossil sea reptiles – the sauropterygians and the ichthyosaurs, which evolved in the early Triassic and in the Middle Triassic respectively – is more controversial. Different authors linked these groups either to lepidosauromorphs  or to archosauromorphs,    and ichthyosaurs were also argued to be diapsids that did not belong to the least inclusive clade containing lepidosauromorphs and archosauromorphs. 
The therapsids came under increasing pressure from the dinosaurs in the Jurassic the mammals and the tritylodontids were the only survivors of the line by the end of the period.
Bird evolution Edit
The main points to the transition from reptile to bird are the evolution from scales to feathers, the evolution of the beak (although independently evolved in other organisms), the hallofication of bones, development of flight, and warm-bloodedness.
The evolution of birds is thought to have begun in the Jurassic Period, with the earliest birds derived from theropod dinosaurs. Birds are categorized as a biological class, Aves. The earliest known species in Aves is Archaeopteryx lithographica, from the Late Jurassic period. Modern phylogenetics place birds in the dinosaur clade Theropoda. According to the current consensus, Aves and Crocodilia are the sole living members of an unranked clade, the Archosauria.
Avialae (birds and their closest relatives)
Simplified cladogram from Senter (2007). 
Demise of the dinosaurs Edit
The close of the Cretaceous period saw the demise of the Mesozoic era reptilian megafauna. Along with massive amount of volcanic activity at the time, the meteor impact that created the Cretaceous–Paleogene boundary is accepted as the main cause for this mass extinction event. Of the large marine reptiles, only sea turtles are left, and, of the dinosaurs, only the small feathered theropods survived in the form of birds. The end of the “Age of Reptiles” led to the “Age of Mammals”. Despite the change in phrasing, reptile diversification continued throughout the Cenozoic. Today, squamates make up the majority of extant reptiles today (over 90%).  There are approximately 9,766 extant species of reptiles,  compared with 5,400 species of mammals, so the number of reptilian species (without birds) is nearly twice the number of mammals.
Role reversal Edit
After the Cretaceous–Paleogene extinction event wiped out all of the non-avian dinosaurs (birds are generally regarded as the surviving dinosaurs) and several mammalian groups, placental and marsupial mammals diversified into many new forms and ecological niches throughout the Paleogene and Neogene eras. Some reached enormous sizes and almost as wide a variation as the dinosaurs once did. Nevertheless, mammalian megafauna never quite reached the skyscraper heights of some sauropods.
Nonetheless, large reptiles still composed important megafaunal components, such as giant tortoises,   large crocodilians and, more locally, large varanids.
Testudines, or turtles, may have evolved from anaspids, but their exact origin is unknown and heavily debated. Fossils date back to around 220 million years ago and share remarkably similar characteristics. These first turtles retain the same body plan as do all modern testudines and are mostly herbivorous, with some feeding exclusively on small marine organisms. The trade-mark shell is believed to have evolved from extensions from their backbone and widened ribs that fused together. This is supported by the fossil of Odontochelys semitestacea, which has an incomplete shell originating from the ribs and back bone. This species also had teeth with its beak, giving more support to it being a transitional fossil, although this claim is still controversial. This shell evolved to protect against predators, but also slows down the land-based species by a great amount. This has caused many species to go extinct in recent times. Because of alien species out-competing them for food and the inability to escape from humans, there are many endangered species in this order.
Sphenodontians arose in the mid Triassic and now consists of a single genus, tuatara, which comprises two endangered species that live on New Zealand and some of its minor surrounding islands. Their evolutionary history is filled with many species.  Recent paleogenetic discoveries show that tuataras are prone to quick speciation.
The most recent order of reptiles, squamates,  are recognized by having a movable quadrate bone (giving them upper-jaw movement), possessing horny scales and hemipenes. They originate from the early Jurassic and are made up of the three suborders Lacertilia (paraphyletic), Serpentes, and Amphisbaenia. Although they are the most recent order, squamates contain more species than any of the other reptilian orders. Squamates are a monophyletic group included, with the Sphenodontia (e.g. tuataras), in the Lepidosauria. The latter superorder, together with some extinct animals like the plesiosaurs, constitute the Lepidosauromorpha, the sister infraclass to the group, the Archosauromorpha, that contains crocodiles, turtles, and birds. Although squamate fossils first appear in the early Jurassic, mitochondrial phylogenetics suggests that they evolved in the late Permian. Most evolutionary relationships within the squamates are not yet completely worked out, with the relationship of snakes to other groups being most problematic. From morphological data, Iguanid lizards have been thought to have diverged from other squamates very early, but recent molecular phylogenies, both from mitochondrial and nuclear DNA, do not support this early divergence.  Because snakes have a faster molecular clock than other squamates,  and there are few early snake and snake ancestor fossils,  it is difficult to resolve the relationship between snakes and other squamate groups.
The first organisms that showed similar characteristics of Crocodilians  were the Crurotarsi, who appeared during the early Triassic 250 million years ago. This quickly gave rise to the Eusuchia clade 220 million years ago, which would eventually lead to the order of Crocodilians, the first of which arose about 85 million years ago during the late Cretaceous. The earliest fossil evidence of eusuchians is of the genus Isisfordia. Early species mainly fed on fish and vegetation. They were land-based, most having long legs (when compared to modern crocodiles) and many were bipedal. As diversification increased, many apex predators arose, all of which are now extinct. Modern Crocodilia arose through specific evolutionary traits. The complete loss of bipedalism was traded for a generally low quadrupedal stance for an easy and less noticeable entrance to bodies of water. The shape of the skull/jaw changed to allow more grasp along with upward-pointing nostrils and eyes. Mimicry is evident, as the backs of all crocodilia resemble some type of floating log and their general color scheme of brown and green mimics moss or wood. Their tail also took on a paddle shape to increase swimming speed. The only remaining groups  of this order are the alligators and caimans crocodiles and gharials.
How Alligators Work
Alligators are absolutely amazing animals. They have been around for millions of years and are about as close as humans will ever get to seeing a living dinosaur. So how and why have they survived so long? They are nearly perfect animals for their environment, including U.S. states like Florida, Georgia, Alabama and Louisiana.
- Alligators can survive two to three years without eating.
- Alligators are one of the few reptiles today that care for their young.
- Alligators have vibration sensors on their skin that are extremely sensitive -- they can detect even the slightest vibration and get out of harm's way long before it arrives.
On the other hand, alligators can be quite dangerous. They are instinctual living machines. An alligator's brain weighs only 8 or 9 grams and would take up only one-half of a tablespoon. This lack of brain power means there is no such thing as a "nice alligator." If it's hungry, an alligator will eat anything that moves. Pets and children who wander near an alligator pond are frequent victims of this instinctive behavior.
American alligators are reptiles, and they are members of the Crocodylia order. In this order are 23 different species, including the American alligator, Caimans and a variety of crocodiles.
The basic Crocodylia body form has been around for over 180 million years, making alligators and crocodiles living dinosaurs. All of these animals have the same basic layout: big heads, long, lizard-like bodies, four stubby legs and long tails.
Male alligators are, on average, about 11 feet (3.5 meters) long and 600 pounds (270 kg). Females are, on average, about 8 feet long and weigh about half as much as male alligators. Males can actually get much larger -- 1,000 pounds is not unusual. At the Alligator Adventures alligator park in Myrtle Beach, SC, a very large crocodile named Utan weighs in at 2,000 pounds and is almost 20 feet long. He is claimed to be the largest living Crocodylian in captivity. (There is a nice interactive presentation on Utan available at the Alligator Adventures Web site.)
Alligators are fresh-water animals and can be found in lakes, ponds, rivers and irrigation canals. Because they are cold-blooded reptiles, alligators are not big fans of cold weather. This limits their range to the warmer, wetter areas in the southeastern United States from Texas to North Carolina.
While there are reports of one alligator, held in captivity, that lived to be well over 100 years old, something like 40 years might be a more typical old age for alligators living in the wild.
Alligators have numerous special features that have allowed them to stick around for 180 million years.
For example, alligators are armor-plated. Bony plates inside the skin, called osteoderms or scutes, make the skin very hard to penetrate. When you look at the ridges on the back of an alligator, each little spike is made by a piece of bone in that section of skin. Click here to see a photo of typical osteoderms.
Even though alligators are huge and cold-blooded, they can be quite fast, with a top speed of 11 MPH (17 KPH) over short distances. For comparison, the fastest humans running at world-record times in a 100 meter dash, are running about 20 MPH (32 KPH), but a typical adult human is no faster than an alligator. This makes it possible for an alligator to escape from most situations on land and get into the water.
Alligator eyes have two sets of eyelids. The outer lids are like human eyelids. They are made of skin and close top-to-bottom. The inner lids are clear and close back-to-front. While an alligator is sitting about or swimming, these inner eyelids protect the alligator's eyes and provide clearer vision in the underwater environment.
When swimming underwater, alligators are water tight. Flaps close off the ears and nostrils, the inner eyelids protect the eyes and a special flap called the palatal valve closes at the back of the throat to keep water out of the throat, stomach and lungs. Alligators can stay underwater for quite a while. A typical dive might last 10 to 20 minutes. In a pinch, an alligator can stay underwater for two hours if it is at rest. And, in very cold water, an alligator can last up to eight hours submerged.
Since alligators are cold-blooded, they have very small lungs compared to mammals. This means that, when running, fighting or wrestling, alligators are using anaerobic respiration (without oxygen) to power their muscles. Mammals, by contrast, use aerobic respiration for most activities like walking or jogging. The only time humans use anaerobic respiration is when doing things like sprinting or lifting weights, which require energy to be produced faster than oxygen is available.
A large alligator can exert itself for at the very most 30 minutes or so before it is completely exhausted. Then it will take several hours for it to recover. This means that one way to capture an alligator is to chase it until it collapses.