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The Biology and Diversity of Extant Reptiles.

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The Biology and Diversity of Extant Reptiles. The word reptile itself does not describe a monophyletic group of vertebrates, like the mammals or birds. It is used to classify a polyphyletic group of animals that are a subset of the larger group of Amniotes. The term is best described through a cladogram: Dr. Paul M. Barrett 2001 The reptiles first appeared in the early Carboniferous, having evolved from labyrinthodont amphibians. They had several distinct advantages over the amphibians that allowed them to flourish during the cold, dry Permian period. These lead them to be the most successful group of vertebrates and this period was referred to as the "age of reptiles." They exploited all terrestrial niches, a few marine and even one group took to the air. No other group of vertebrates had ever displayed such diversity and mammals today are their only match. They were the first group of tetrapods to successfully overcome the major problems of terrestrial life, namely desiccation, thermoregulation and respiration. Adaptations to withstand desiccation Unlike amphibians reptiles are able to tolerate dryer conditions and avoid desiccation. ...read more.


This means that the lung can be large and independent of the buccal cavity, there is no mixing of the stale and the new air, allowing the buccal cavity to develop separately. Overall a higher metabolic rate is now possible. Diversity of the reptiles The reptile group can be firstly divided into two main sections, the parareptilia (anapsids) and the diapsids. What sets these two groups apart is that the diapsids have two pairs of temporal fenestrae (holes) one upper and one lower. These allow for the attachment of muscles for the jaw although some reptiles have lost one or even both through their evolution. Parareptiles (anapsids) have no such fenestrae. Parareptiles Chelonia (Turtles and Tortoises) This is the only group alive today and comprises of about 250 species. They have a long evolutionary history, the earliest known turtle being Proganochelys, arising in the Late Triassic of Europe and southern Africa. They form two lineages based on the way they retract their head into their shell, the Cryptodira (80% of species) bend their neck in a straight line into their shell whilst the Pleurodira bend their neck sideways in the bilateral plane. ...read more.


To move quickly or over long distances they adopt a "high walk" a semisprawling gait. There are some examples of galloping and even some of them becoming bipedal. They have bony plates underneath their scales along their back called scutes. These are connected to the backbone via a series of tendons and help brace the crocodiles back whilst it is on land, something like a suspension bridge. Unlike the chelonia, crocodiles do show a great deal of parental care, they build and guard nests, help their young to hatch and acre for their young in nursery pools for several weeks after hatching. Summary As seen from this essay the diversity and subsequent biology of reptiles is very wide and encompasses many niches. However reptiles today are nowhere near as prolific as they were in the Mesozoic era where they ruled the earth and exploited hundreds, if not thousands, more niches. The real diversity and biology of reptiles was seen about 60 million years ago, before the mammals got a hold. But the only way to investigate that is through the fossil record and that will never give us all the information needed to draw a complete picture of reptile diversity. ?? ?? ?? ?? Chris Holland Jesus College - 1 - ...read more.

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