[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: the definition of Reptilia
On Sat, 1 Dec 2001, David Elliott wrote:
> Have reptiles been formally defined, and if so, what are they?
> I've heard them referred to as an unnatural group (diapsids excluding
> dinosaurs), and - of course - as synonymous with "diapsid",
I've never heard of either of those usages.
> but the thing that inspired me to ask was the fact that non-mammal
> synapsids are referred to as "mammal-like reptiles".
Incorrectly, at least if you're using phylogenetic taxonomy.
> So if you include all descendants of the common ancestor of those
> animals commonly referred to as reptiles, we should be they (so
> Reptilia = Amniota). Aesthetically, i like this (because the presence
> of the term "mammal-like reptile", and also: in my little brain
> "reptile" conjures up the concept "tetrapod adapted to dryness" more
> strongly than it does "diapsid" (and even more strongly than "outdated
> paraphyletic group"), but i thought i'd better ask to see how things
> really are.
Interesting concept, but _Amniota_ is a better name for the clade, anyway.
(_Reptilia_ means "creepers")
> So has it been formally defined, or is it one of those common words whose
> appropriateness everybody has a different idea about?
There are a lot of different ideas about it (it originally included
sharks, apparently). Here are the major ones:
traditional: any amniote that is not avian or mammalian
phylogenetic: the most recent common ancestor of _Crocodylus niloticus_,
_Lacerta agilis_, and _Chelonia mydas_*, plus all of its descendants
(* I think that's the type species...)
The former includes non-mammalian synapsids (the traditional _Synapsida_
did not include mammals, BTW) but not avians. The latter includes avians
but not synapsids.
Personally, I'd like to get rid of the term, but it doesn;t seem to be
going anywhere anytime soon....
T. MICHAEL KEESEY
The Dinosauricon <http://dinosauricon.com>
personal <firstname.lastname@example.org> --> <email@example.com>
AOL Instant Messenger <Ric Blayze>
Yahoo! Messenger <Mighty Odinn>