Reptiles (was Re: Dinosaurian Class)

["Thomas R. Holtz, Jr." <th81@umail.umd.edu>]

At 05:23 PM 6/21/98 -0700, you wrote:

>>      Amniotes
>>        Synapsids
>>
>>        Sauropsids
>>          Diapsids
>>            Archosaurs
>>
>
>Where do Pareiasaurs and other "stem reptiles" fit into this scheme?

Under most schemes, the "Anapsida" or "Parareptilia" (pareiasaurs,
procolophonids, etc.) would be another clade within Sauropsida outside Diapsida.

>Am I just cynical, or does it seem to others that the Synapsids are 
>placed outside the "Reptilia" ("all other amniotes") clade in order to 
>avoid refering to the "fabulous furballs" (mammals) as "reptiles"?

Yes, you're just being cynical... ;-)  (Well, you set yourself up for that
one).  Seriously, the work of Gauthier and colleagues was based on very
detailed analysis of soft and hard tissue characters, which really strongly
show that mammals lie outside a clade comprised of turtles, lepidosaurs, and
archosaurs.  The latter three really do share a LOT of features of anatomy &
physiology that are not found in mammals.  Among the characters preserved in
the skeleton, these three groups and their extinct relatives do share a lot
of derived features not found in primitive synapsids.  Regardless of where
the name "Reptilia" is placed on the tree, there is very, very strong
evidence that mammals and their ancestors lie outside a clade comprised of
turtles, lepidosaurs, crocs, and birds.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661