Division and Classification Essay Animals that breath air and have scales on the exterior of their body are referred to as reptiles. Reptiles have been dated back to have been on the earth for the past 315 million years, though not all species are extant in modern times. All reptiles are ectotherm, which means they are “cold-blooded” animals (whereas most mammals are warm-blooded). All reptiles are also tetrapods, which mean they have four limbs (or they have descended from four-limbed ancestors).

In general most reptiles are oviparous (egg-laying), with the exception of some viper and constrictor snakes that give live birth. In regards to size, reptiles can be anywhere from a tiny 0. 6 inch gecko all the way up to a 20 foot crocodile weighing in at 2,200 pounds. With the exception of Antarctica reptiles inhabit every area of the earth. Reptiles are recognized as being classified into four separate domains (categories) which are, Crocodilia, Sphenodontia, Squamata, and Testudines (Wikipedia, Reptiles).

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The domain Crocodilia contains the family’s alligator, caimen, crocodile, and gharial. There are twenty-three species contained in this domain, and they are the closest living relatives to birds. This order had been in existence for the past 84 million years since the dawn of the Cretaceous period. The crocodilian species ranges in size from a four to five- foot Cuvier’s Dwarf Caimen, all the way up to the twenty-foot Saltwater Crocodile (which is actually the largest out of all extant reptiles). Species within this domain have an average life span of seventy to one hundred years.

Crocodilians are the only domain of reptiles that have a four-chamber heart, the usual in all other reptiles being either a three of five chambered hear. It is common for only warm-blooded animals (such as mammals and birds) to have a four chambered heart. But since Crocodilians ancestors were warm blooded it is believed they kept this extra valve to help shunt oxygen depleted blood to the stomach to help create more stomach acid to help break down bones (Wikipedia, Crocodilia). Crocodilians have a relatively small brain, but in comparison to other reptiles it is more advanced.

They have very good night vision and are also able to see under water well (though they tend to rely on other senses more when submerged). Depending on the size of the animal within the domain, Crocodilians eat a wide variety of things. Smaller animals within the domain eat anything from insects to other small reptiles, whereas larger apex predators such as the Alligator and the Crocodile can eat small animals all the way up to deer, zebra, and even humans if provoked and given the opportunity.

Crocodilians replace their teeth on a constant basis throughout their life. Their teeth grow within each other so when one breaks there will be a fully grown one waiting inside. Crocodilians teeth development slows as they age. There have been witness accounts of some old crocodilians being toothless due to their age and the fact that teeth production has by that time slowed to a complete stand still. Crocodilians have been known to go through three-thousand teeth in their entire life (Wikipedia, Crocodilia).

The order Sphenodonita is the smallest out of the four orders. There is only one living genius containing two species of the Tuatara (Sphenodon). The Sphenodontia order dates all the way back to the Mesozoic era more than one-hundred million years ago. It is only found in the country of New Zealand and the people of New Zealand (the Maori) believe them to be scared creatures. Most of their domain died off back around the time of the extinction of the dinosaurs, but some survived since they were separated on an island later to be New Zealand.

Tuataras are generally twenty-four inches in length and two pounds in weight; there is no range in size in this domain since only two species exists. Tuataras are mainly sit- and-wait predators and mainly eat invertebrates. 75% of their diet consists of large, flightless insects. Reproduction takes two to five years to be commenced and completed, which is the slowest for all reptiles. Tuatara can continue growing for up to the first thirty-five years of their life. The Tuatara has been on the endangered species list for the past one-hundred years (Wikipedia, Sphenodontia).

Squamata is the largest and most recent order of reptiles, including the species lizards, snakes, and worm lizards. The order is about one-hundred and sixty million years old and has approiemently 7,900 species in this domain. Species in this order are distinguished by their scales, which have a horny shape. Also species in this domain have a movable quadrate bone, making it possible for them to move their upper jaw. This is very observable in snakes; especially the anaconda which can eat an animal five to six times its size, such as deer and hippopotamuses.

Besides the larger snakes in the Squamata order all other eat small to medium sized invertebrates. Out of all the orders the Squamata order has the most variance in size-range. On the small side the Jaragua Sphaero is 0. 63 inches in length and is one of the world’s two smallest know reptiles, and on the opposite end of the spectrum the Green Anaconda can be up the twenty-two feet in length and weight up to two-hundered and fifty pounds (making it the heaviest known snake species) (Wikipedia, Squamata).

Squamata males have hemipenis witch stay inverted in the body until it is time for reproduction. At that point they function the same as a human penis since they are then erected via erectile tissue outside of the body. This is the only reptile group that contains both viviparous and ovoviviparous species. And some species like the Komodo Dragon actually can undergo asexual reproduction via parthenogenesis (the duplication of haploid reproductive cells without fertilization).

Squamata are also the only order that had the ability to shed its “skin” in one entire piece (Wikipedia, Squamata). The order Testudines contains over three-hundred species of turtle. It is one of the oldest orders of the reptiles being two-hundred and fifty years old. Nearly 71% of the order is either extinct or endangered. Turtles are characterized into this order by the bony or cartilaginous shell that develops on their rib cage (the shell is internaly connected to their body and is part of their skeleton).

Turtles are sub-categorized into two separate groups, the Cryptodira, which can draw their necks in while contracting it under their spine; and the Pleurodira, which contract their necks to the side, and are in general smaller than the latter. These differences were formed through evolution as resolutions to the troubles certain species had with withdrawing their neck into their shell. Many turtles are herbivores and feed primarily on plant matter. Since they are slow movers, turtles lack the ability to actively pursue prey.

Testudines differ from all other living reptiles in that testudines do not have temporal fenestrae. Temporal fenestrae are holes in the sides of the skull, either above or below the eyes. Turtles lay eggs during reproduction then lay them in soil to incubate for 60 to 140 days before they hatch (Wikipedia, Turtle) The Mesozoic era is commonly referred to as the “Age of Reptiles” since most dominant animals of the time were reptile (such as dinosaurs). The end of the Cretatous period is when the extinction of the dinousaurs occurred, and so the end of the “Age of Reptiles”.

Out of all the marine reptiles only the sea turtles remain, and from the dinosaurs, only certain tiny animals in the form of birds survived. That brought on the “Age of Mammals” which later brought rise to our own race becoming a predominant part of the ecosystem later. Though there age may have ended there are still a large number of reptiles in this world. There are 8,700 extant species of reptiles, compared with 5,400 species of mammals. They are a very large and intricate factor in the smooth and stable functioning of our ecosystem.