What is a reptile?

David L Rowe (UK) This is a short introduction to what is a reptile – an issue that is a lot more complex that it might seem. To understand what a Reptile is one first needs to understand the cladistic (which is a way of classifying life forms) method and phylogenetic systematics (that is, a way of establishing the relationship of life forms) used by palaeontologists. Skull structure is the most important factor to be considered. The term ‘Reptile’ refers to the Class Reptilia, which includes the ectothermic (cold-blooded) turtles, snakes, lizards, crocodilians, tuataras and dinosaurs, and the endothermic (warm-blooded) birds, which are also referred as non-avian dinosaurs. However, the way in which body temperature is maintained (cold versus warm-blooded) is not a factor in the classification of Reptiles. The main diagnostic physical characteristic of a Reptile that separates them from other animals is that they are Diapsids (Fig. 1). A Diapsid has a pair of openings in the skull – temporal fenestra – behind the eyes. Turtles and a few extinct Reptiles are an exception and have no temporal fenestra. They are classified as Anapsids. Fig. 1. Diapsid skull. Birds are descended from or are dinosaurs (depending on your view) with which they have shared derived traits including being Diapsids. Therefore, dinosaurs and birds are classified as Reptiles. However, birds are certainly quite different from other living Reptilia. The traits that modern birds possess started with the first Diapsid, the tiny lizard-like Petrolacosaurus, about 350 million years ago. Modern … Read More

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