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Re: Perching, climbing, roosting was Re: 11th specimen of Archaeopteryx
On Sun, Nov 13, 2011 at 7:20 PM, Anthony Docimo <email@example.com> wrote:
> Weren't stem-mammals traditionally regarded as reptiles?
> Odd, strange reptiles, but still reptiles.
Yes, under the traditional usage of "reptile" to mean all amniotes
except avians and mammals. But traditional Reptilia is a wastebasket
taxon, and many have moved away from that usage (or, indeed, against
using "Reptilia" in a formal sense at all).
It should be noted, though, that traditionally stem-mammals were not
considered phylogenetically closer to living "Reptilia" (lepidosaurs,
testudines, crocodylians) than to mammals. As now, they were thought
to share more ancestry with mammals than with other amniotes, but they
were still relegated to the "Reptilia" wastebasket.
You could almost see the traditional system as "merit-based". To
escape a class, you have to evolve "enough". Thus, reptiles "escaped"
Amphibia by evolving amniotic eggs and dry skin. Birds "escaped"
Reptilia by evolving feathers, flight, and endothermy. Mammals also
"escaped" Reptilia, by evolving hair, mammary glands, and endothermy.
Needless to say, this is a very subjective system. A more scientific,
phylogeny-based system has been gaining acceptance in recent decades.
The only formal higher taxa recognized under this system are clades:
taxa consisting of an ancestor and all descendants.
Some workers use "Reptilia" to refer to the least inclusive clade
containing the extant animals traditionally considered reptiles, i.e.,
lepidosaurs, testudines, and crocodylians. This usage includes birds
as a type of reptile, and excludes Synapsida (mammals and
stem-mammals). Others just don't use the term "Reptilia". (I've also
seen a proposal to limit "Reptilia" to just the lepidosaurs, but this
has not been followed.)
"Sauropsida" is an old name for the clade stemming from the earliest
ancestor of lepidosaurs, testudines, crocodylians, and avians which
was not also ancestral to mammals. It has seen a resurgence in use
more recently. (It was coined along with "Theropsida", which was meant
for the clade stemming from the earliest ancestor of mammals which was
not also ancestral to lepidosaurs, testudines, crocodylians, and
avians. "Synapsida" is generally used for that clade nowadays,
T. Michael Keesey