[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Air sacs in extant non-avian reptiles?



There seem to be multiple misconceptions in this exchange.


>In a message dated 7/31/00 11:02:33 AM, ornstn@home.com writes:
>
><< Here Mr Lurio is wrong.  First of all, naming only becomes political if
>you
>let it do so, and there is no need for this (creationists aside).  But
>since there seems to be a very good argument for excluding Synapsida from
>Reptilia on the grounds that they were separately derived from early
>tetrapods, a chicken is considerably more of a reptile than you are because
>some of its ancestors were reptiles, while none of yours (or mine, or even
>Mr Lurio's) were.  We are, of course, all amniotes (or tetrapods, if you
>like). >>
>
>No there isn't. We don't know that they were seperatley derived from early
>tetropods, are you saying the aminiotic egg evolved more than once? The
>simple fact is that the earliest diapsids are from the same carboniferous
>strata as the earliest synapsids.

I think there are two different applications of the word "reptile" involved
here.  The application favored by Mr. Lurio refers to a level of biological
organization (to borrow Tom's phrase) - anything that lays an amniotic egg,
but isn't properly endothermic or covered with fur or feathers.  This is
obviously not a monophyletic group.

The other, which is favored by many systematists (I do not believe the
percentage is known), is phylogenetic.  It refers to the last common
ancestor of living turtles, lepidosaurs, and crocodylians and all of its
descendents.  Birds are ultimately derived from this ancestor, and are
phylogenetically reptiles.  Mammals are not, and are thus not reptiles.  In
this scheme, the amniotic egg arose only once, but the ancestral amniote
was not a reptile, because "reptile" is no longer a wastebasket for
non-mammalian non-avian amniotes.




>
>I distinctly remember a cover story in Nature about how they found a turtle
>ancestor. This was before some cladist decided that it must be a diapsid and
>then the beastie was all of a sudden surpressed.
>

Not quite.  Not all cladists think turtles are diapsids, and most of the
molecular systematists who put turtles among diapsids use likelihood
methods (and are thus not really "cladists" in the classical sense).  The
turtle "ancestors" were already-known taxa, such as pareiasaurs, and the
cladogram drawing turtles close to them was controversial long before any
of the papers putting turtles within Diapsida were published.  You will
still find these animals in textbooks - nothing has been suppressed.

Also - in reference to an earlier post, could you please explain your
accusation that museums "steal fossils?"  As a museum employee, I am very
interested in this - if my colleagues are involved in theft, I should try
to stop it.



chris



----------------------
Christopher A. Brochu
Department of Geology
Field Museum of Natural History
1400 S. Lake Shore Drive
Chicago, IL 60605

voice: 312-665-7633
fax: 312-665-7641
electronic:  cbrochu@fmppr.fmnh.org

http://www.geology.uiowa.edu/faculty/brochu/