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Re: dinosaur synapomorphies?




Dear All,
It amazes me that so many people now take the holophyly of Dinosauria for granted. Many of the purported synapomorphies are very weak, and many remind me of the "kitchen list" of synapomorphies that was proposed for Ornithodira (sensu stricto).
Sereno himself points out that some of these synapomorphies are not present in Sauropods or other groups of dinosaurs. And many of these synapomorphies involved the pelvis and hind legs, and being interconnected changes in the evolution of an "abductor-based balancing system", they could have happened more than once (just like the development of the perforate acetabulum).
Therefore I will be concentrating on the deltopectoral crest (no. 8) and three skull characteristics (2, 4, and 5) in the Sereno list that Tom gave below. In my opinion, skull character 1 is very weak. I'm just looking for a few "strong" synapomorphies that I can really believe in, but am not having much luck so far. If there are a couple of strong ones, then weaker ones can be used to support a case for holophyly for dinosauria. If not, then maybe Romer and others were right all along.
------Ken Kinman
********************************************


From: "Ken Kinman" <kinman@hotmail.com>
Reply-To: kinman@hotmail.com
To: dinosaur@usc.edu
Subject: dinosaur synapomorphies
Date: Fri, 24 Aug 2001 18:05:43


Dear All,
Following up on my last post, I would like to reopen the discussion we
had when I first joined DML in May 2000.
Which of the synapomorphies given by Sereno (see below) are the
strongest (and are they unique to the dinosauria clade)? Any good dinosaur
synapomorphies not in Sereno's list?
------Thanks, Ken
P.S. BTW, I would point out to Jaime and others that the possibility of
reversals in some of these "synapomorphies" (such as the perforate
acetabulum, as noted below), shows that reversals (as pseudo-synapomorphies)
can even be a problem for the relatively well-known vertebrate groups. But
as I noted yesterday, it's even more problematic in invertebrates.
*******************************************
From: "Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>
Reply-To: tholtz@geol.umd.edu
To: <kinman@hotmail.com>, <dinosaur@usc.edu>
Subject: RE: dinosaur synapomorphies
Date: Tue, 16 May 2000 09:21:55 -0400

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Ken Kinman
>
> Yes, I know about the Novas paper, but which of his listed dinosaur
> synapomorphies do other workers find the most convincing?
> Three or more sacral vertebrae is one of his listed
> synapomorphies, but
> I don't find that very convincing (especially if Staurikosaurus has only
> two; other exceptions??). And an open acetabulum could have also arisen
> twice, once in ornithischia and once in saurischia.


Actually, it could have arisen independantly in every species: that,
however, would not be the most parsimonious explanation.

In any case, given that herrerasaurids and _Saturnalia_ each have at best a
semi-perforate acetabulum, a fully perforate condition may have arisen
independantly in theropods and sauropodomorphs (and thus independant as
well
in ornithischians). Alternatively, herrerasaurids and _Saturnalia_ could
have revereted to the ancestral condition.


>      Are there any good synapomorphies away from the back area
> (hind limb &
> pelvis) of the animal, especially in the skull?  I remember someone
> suggesting that "elongate vomers" could be a dinosaur
> synapomorphy, but that
> sounds so vague.  Does anyone have specific information on this
> or any other
> dinosaur skull synapomorphies?

A big problem here is the lack of knowledge of the skulls of the immediate
outgroups of Dinosauria.  We have a pretty good knowledge of the hindlimb
anatomy of these guys, but very little knowledge of their heads: thus, we
can say with more certainty what hindlimb characters dinosaurs have that
their relatives lacked, but not so for the skulls.

Here are Sereno's (1999. Science 284:2137-2147) dinosaurian synapomorphies:
1. Postfrontal absent
2. Frontal participates in supratemporal fossa
3. Ectopterygoid dorsal to pterygoid
4. Quadrate head exposed laterally
5. Posttemporal opening reduced to small foramen
6. Dorsosacral (3 sacrals)
7. Ossified sternal plates present
8. Deltopectoral crest 35% or more of humeral length
9. Manual digit IV narrower than digits II and III without terminal ungual
10. Brevis fossa present
11. Femoral greater trochanter angular
12. Femoral medial tuberosity small
13. Cnemial crest present
14. Astragalar ascending process present
15. Astragalar anterolateral process lateral to calcaneum
16. Calcaneal medial process rudimentary
17. Distal tarsal 4 heel shallow
18. Metatarsal IV shaft sigmoid in anterior view


Of these, Sereno codes _Lesothosaurus_ as lacking #17; Sauropoda lacking 3,
10 & 18; and _Eoraptor_ lacking 7; I might have coded some of the other
taxa
differently on top of that, and used a few additional characters. However,
this is a very good starting point.


              Thomas R. Holtz, Jr.
              Vertebrate Paleontologist
Department of Geology          Director, Earth, Life & Time Program
University of Maryland         College Park Scholars
              College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone: 301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661      Fax (CPS-ELT): 301-314-7843



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