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Re: Removing segnosaurs from Theropoda
At 12:21 PM 8/30/95, Stan Friesen wrote:
> From: email@example.com (Jason Head)
> > As for "Thecodontians", you don't have to be a
> > cladist (and/or strictly adhere to monophyletic groupings), to recognize
> > that "thecodont" has NEVER described an actual group of related taxa. It
> > was a garbage can ( a la megalosaur), for poorly understood archosaurs, and
> > has since been abandoned.
>And, pray, what other name is available for stem-archosaurs?
> Pray, there are multiple names to describe the varied lineages of
>basal archosaurs (which have already been posted). But first, Colbert,
>1965, defines thecodonts as follows: "Another reptilian order that arose
>during the Triassic period were the thecodonts, the first of a group of
>related reptilian orders, collectively known as the archosaurs. The
>thecodonts evolved as pseudosuchians, a varied group of reptiles, some
>large, some small, and as the phytosaurs, uniformly large,
>crocodilian-like animals. All thecodonts became extinct at the end of the
>Triassic period." Pseudosuchia is now crurotarsi (or vice versa,
>depending on which phylogeny you choose). Phytosaurs are now considered
>nested w/ in crurotarsi, rendering Colbert's definition a bit odd. In
>addition, if you follow the definition of thecodont as per Colbert, what
>is to become of Proterosuchus and our beloved Euparkeria? In addition,
>how does one use the indentary plates of "thecodontia" to resolve
>dinosaurian systematics, when the plates appear and disappear throughout
>the various lineages so paraphyletically defined? Which member of the
>thecodonts will you use for your outgroup(s): aetosaurs? riojasuchids?
>Rutiodon? Using paraphyletic groups in fine for paleontology in
>situations where you want to discuss a lineage of critters, w/ out
>involving their DIRECT descendants. That was the crux of my posting a few
>weeks back. What, besides Triassic extinctions, can be discussed about
>thecodonts, that doesn't also imply dinos', pterosaurs, and crocs'? If
>you want to snip birds off of the dino' tree to talk about the big, dead
>fellas, fine- but to snip dinos' pteros' AND crocs' off of archosauria (ne
>"thecodontia")? What information will that give you?
Colbert, E. H., 1965. THE AGE OF REPTILES. The World Naturalist, R.
Sereno, P. C., 1991. Basal Archosaurs: Phylogenetic Relationships
and Functional Implications. Society of Vertebrate Paleontology Memoir 2,
Jason J. Head
Dept. of Geological Sciences
Southern Methodist University
Dallas, Tx. 75275
"I usually just make sh*t up" - discussion on oral presentations.