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Re: Synapsids weren't reptiles?

----- Original Message -----
From: "T. Michael Keesey" <keesey@gmail.com>
Sent: Tuesday, July 01, 2008 6:00 AM

A decent model might be something like [...] _Eothyis_ (an early synapsid):

*Eothyris* (with r) is only known from a skull, so while the rest of the reconstruction is certainly not far off, we don't actually know that.

What was he anyhow, if he wasn't a reptile, adn wasn't an amphibian?   A

No, just an amniote. As the ancestral amniote, it couldn't be classified with any more detail than that.

This is a big difference between rank-based nomenclature and phylogenetic nomenclature: in the latter, but not the former, it is possible to be _just_ an amniote -- which is the only option that makes sense for the last common ancestor of theropsids and sauropsids.

You seem to be saying there were land bound tetrapods who were neither
amphibians nor reptiles - what were they?

Tetrapods, period.

Not to mention the fact that there are many more options: baphetids, anthracosaurs, seymouriamorphs... all of these were tetrapods* but neither amniotes nor amphibians. Amniotes and amphibians are just two branches on a large tree!

* In the traditional sense.