Re: Synapsids weren't reptiles?

[David Marjanovic <david.marjanovic@gmx.at>]

----- 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):
> http://upload.wikimedia.org/wikipedia/commons/f/f6/Eothyris_BW.jpg

*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
> > fish?
>
> 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.