Turtles and crocodilians no longer reptiles


Turtles and crocodilians no longer reptiles

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My introductory biology course taught that living four-legged vertebrates are divided into four classes: amphibians, birds, mammals, and reptiles. This has been viewed as problematic for awhile now because birds have been shown to be the closest living relatives of crocodilians. There has been a question of what to do with them as a result. Do we just leave well enough alone and keep everything paraphyletic? Or do we try to attempt to create more natural groups by putting birds and crocodilians closer to each other in their own class or putting birds into Reptilia?

The Center of North American Taxonomy (CNAH) seems to think they have an answer. They've recently revised their modern taxonomy and come up with a solution that probably will surprise a lot of people.

Quote:
Over the past two decades, evidence has accumulated that recognition of the Class Reptilia is not consistent with evolutionary history. However, due to historical inertia, the herpetological community has been reluctant to incorporate nomenclatural changes consistent with contemporary phylogenetic discoveries. In order to clarify this situation, CNAH has adopted the following classification based on the phylogenetic hypothesis presented below.
Class Reptilia has been traditionally composed of Order Chelonia (the turtles), Order Crocodylia (the crocodilians), Order Squamata (the lizards, snakes, and amphisbaenids), and Order Rhynchocephalia (the Tuataras). The discovery that birds (Class Aves) are the closest modern relative to the crocodilians, or the sister clade to crocodilians and turtles, renders the Class Reptilia as an unnatural grouping. In order to reconcile the taxonomy with evolutionary history, the following classification is adopted by The Center for North American Herpetology until further data suggest otherwise. Due to the arbitrary nature in which higher taxa may be delineated, CNAH has tried to reach a classification in which the maximum explanatory power is retained.

Jura has put forth his thoughts on the matter, offering a historical review of the situation that climaxes with a negative outlook on CNAH's decision. Removing crocodilians and turtles from Class Reptilia is not a bad way to resolve the problem, but as someone else has pointed out: 1) "Chelonia" wasn't the best choice for the turtle class name; and 2) it might have been better do away with Reptilia entirely, and call the tuatara/squamate class "Lepidosauria" instead.

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user-icon Submitted by Technosaurus on Sat, 2008-07-19 22:25.

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