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The Relationships between Reptiles and Other Animals Past

and Present

Introduction

Reptiles are the most diverse group of land vertebrates with nearly 8000 representative

species. There were many more ancient groups of reptiles which are now extinct, but still

form part of the reptile family tree. One can only begin to understand the similaritiesbetween reptiles and other classes of animals by going into the past, to understand what

groups of animals diverged from the different reptile lineages and at what time. This

article requires us to delve into the realms of paleontology; this can be an interesting field

for herpetologists as there are many interesting and unique extinct reptile species whichhad physical features and behaviors that are not seen in modern reptiles.

The Beginning

Reptiles evolved from amphibians around 310 million years ago in a time period known

as the Carboniferous period, the worlds major coal fields were laid down at this time.These reptiles would have started out as primitive lizard like creatures. They flourished

and dominated the landscape during this period, evolving into many diverse species.

These reptiles would have lived in a warmer climate than today. The vegetation wouldhave been consisted of giant club moss trees and ferns; there would have been no grass or

flowering plants. A time traveler you would not have been able to give a bouquet of

flowers as a gift until the late Cretaceous.

The Rise and Fall of the Mammal Like Reptiles

The Permian period lasting from 300 to 250 million years ago gave rise to a branch of

reptiles called Mammal Like Reptiles. These animals are a branch of reptiles which had

certain traits in common with mammals such as a fused lower jaw and an upright stancewhich would resemble that of a dog rather than a lizard whose belly nearly reaches the

ground. Mammal Like Reptiles were highly successful and were the dominate group of

animals at the time. These reptiles turned out to be a dead end in the history of reptiles as

they were wiped out along with 90 percent of life on earth during the Permian massextinction 250 million years ago. This was the first mass extinction that reptiles survived.

Actual mammals only appeared in the late Cretaceous over 100 million years after the

Mammal Like Reptiles went extinct.

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Enter the Triassic and the Rise of the Dinosaurs

The Triassic Period was the hottest period in earths history as the temperature had

increased by a world average of 20 degrees Celsius during the Permian extinction.Reptiles thrived on the super continent Gondwanaland. The reptiles then branched of into

two groups: The lizard like reptiles and the Crocodile/Dinosaur/Bird group of reptiles.Tortoises, Turtles and Terrapins are a separate branch. The first Dinosaurs appeared in

the Triassic having branched of from other reptiles. Dinosaurs have more in commonwith crocodiles and birds than with lizards or snakes. Reptiles and Dinosaurs faced

another mass extinction in the late Triassic 200 million years ago, both groups survived.

The Jurassic: Modern Reptile Orders Complete and Further

Diversification of the Lizard like Reptiles

By the mid Jurassic the modern orders of reptiles had become complete with theappearance in the fossil record of the last reptiles to evolve the snakes at around 100million years ago. In the Jurassic flying reptiles (Pterodactyls) and marine reptiles

(Plesiosaurs and Mososaurs) branched off from the lizard like reptiles, these reptiles are

more closely related to lizards than dinosaurs. Dinosaurs diversified further during this

time.

The Cretaceous Mass Extinction and the Appearance of Birds

A meteorite collided into earth 65 million years ago causing a mass extinction that wipedout the dinosaurs and the flying and marine reptiles. This is the third mass extinction that

reptiles survived. Birds branched off from the dinosaurs and have now been recognizedas their direct ancestors.

All living and extinct reptiles, Dinosaurs, Crocodiles and birds have been placed in a

group called the Sauropsids. All these animals can be placed together, as they havesimilarities with each other that they do not have with any other group of animals. Birds

are placed in this group as they have more in common with reptiles than they do with

mammals. Some authorities consider birds to be reptiles.

The above conclusion is based on Cladism. A clade is set of animals consisting of anancestor and all its descendants. This is a new form of taxonomy which is considered

more accurate for scientific classification but far more complicated than standard

taxonomy.

Read more about reptiles on the authors Blog

http://www.timsreptiles.co.za/http://www.timsreptiles.co.za/