The colloquial definition of a reptile is any and all scaly, "cold-blooded", sprawling animals that make most people go *ick*.Meanwhile the cladistic definition of a reptile is pretty wide ranging. It states:
Any creature descended from the closest relative to chelonians, crocodilians and squamates.In this definition birds are reptiles.
So then what is a reptile? Well let's think about what makes a reptile a reptile. Well, first off you need to have, or be descended from, an ancestor that had four limbs. These creatures are known as tetrapods and include all reptiles (including birds), amphibians, and mammals.Next thing you need are scales. Scales are these awesome pieces of epidermis made from the coolest protein around keratin. Now keratin makes up all kinds of things like hair, fur, fingernails, rhino horns, feathers and reptile scales. All reptiles have scales. Of course fish have scales too, but they lack four limbs and didn't descend from an ancestor that had four limbs, so scales still work. Mammals don't have scales so their out, but birds do have scales and they are tetrapods. Plus bird feathers are comprised of nearly the same type of keratin as reptile scales so birds are technically considered reptiles. Amphibians as cool as they are, don't have scales and therefore are not reptiles.
So what about everything else, like egg laying? Even though there are lots of oviparious (egg laying) reptiles, there are also quite a few reptiles that give birth to live young, just like mammals. And speaking of mammals, the monotremes, which are a very archaic form a mammal, are egg layers. So no egg laying doesn't make a reptile.Do you have to have a sprawling posture? Most definitely not. Birds, deinosaurs, crocodylians and other reptiles lack the sprawling posture that has long characterized the reptilia.
Confused yet? It seems that the real big definer of a reptile is the scales. Other things that are usually associated with reptiles are a more primitive internal system along with "cold-bloodedness". But, it seems that there is always a reptile out there that is the exception to the rule.Want to learn more about these fascinating and staggeringly diverse array of creatures, then just head on down below and click on the group of animals that you want to read more about.
And here is a list of the extinct taxa of reptilia. Each one will hopefully cover it's respective area fairly wellMind you the reptilia is so diverse that it could take awhile to have them all up, but I'll try to go fast, while still keeping it thorough.
|All the other saurs that I can't think of at the moment.|