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Re: Synapsids weren't reptiles? I'm confused.

On Wed, Jul 2, 2008 at 6:15 PM, Garth Godsman <maniraptor@yahoo.com> wrote:
> Thanks again Michael
> Okay, the split has occurred and we now have identifiable, but primitive,
> synapsids and, what was the term, sauropsids? (Are all of what are
> referred to commonly as reptiles sauropsids?)

Ha, depends on the usage of "reptile". If we're just talking about
extant animals, though, then yes. Turtles, tuataras, squamates,
crocodylians, and avians are sauropsids. (Tuataras and squamates are
lepidosaurs, avians and crocodylians are archosaurs, and turtles ...
are bizarre mystery sauropsids.)

> Other than the skull openings, is there anything else that would identify
> one from the other? Someone mentioned scales, uric acid and something else
> which escapes me for the moment, though surely these would be speculations
> going that far back in time.

Skull fenestration (which is what "Synapsida" is named for). Early
sauropsids have the ancestral condition of a "solid" rear skull (as do
turtles), while all known synapsids (I think) have a derived
condition, with a lower temporal fenestra.

Most synapsids also have differentiated teeth (selves included), while
most sauropsids have teeth that all look the same. There are
exceptions, of course. The earliest synapsids are homodont, as are
some derived ones like cetaceans. And some derived sauropsids, like
heterodontosaurids, are heterodont (hence the name).

There are other skeletal characters as well, but I'm not that familiar
with them.
T. Michael Keesey
Director of Technology
Exopolis, Inc.
2894 Rowena Avenue Ste. B
Los Angeles, California 90039