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

Re: Regarding Phytodinosauria, Saurischia, and so forth



At 12:52 AM 8/13/95, Dinogeorge@aol.com wrote:
>Judging by the feet alone, Segnosauria could not have diverged from the
>theropodomorph clade anywhere above the point where pedal digit I
>retroverted, that is, slightly above Herrerasauria (and certainly not within
>Tetanurae). That's as close to being theropod it could have come.
>Furthermore, the small, blunt teeth and downwardly curved dentary with "chin"
>are commonly found among phytodinosaurs (Sauropoda, Prosauropoda,
>Stegosauria, some Ornithopoda), never in theropodomorphs. The skull of
>_Erlikosaurus_ can be derived fairly straightforwardly from the skull of
>_Plateosaurus_, although the latter is too derived to be the true segnosaur
>ancestor. The worst convergence problem is presented by the very
>theropod-like forelimbs, but even those may be derived from prosauropod
>forelimbs without invoking significant character reversals.

        Well, I have to disagree with you on this one, George, because I've
already described a new dinosaur ichnogenus of a truly aberrant theropod
with functionally tetradactyl feet, and the prints were _not_ made by
therizinosauroids. The toes radiate out ina  stellate, not subparallel,
manner, as in the therizinosauroids.  The toes are incredibly long and very
skinny, and have short claws at the ends.  In fact, if you cut of the
imprint of digit I, it's look almost exactly like an emu print, only with
skinnier toes.  The creature had a very compact distal end of the
metatarsus, not all splayed out like therizinosauroids.  The prints (no
trackway as yet) average just over 30 cm long --  a moa sized creature.
More likely than not, it was a "coelurosaurian" theropod, but with a
functional, non-reversed digit I.  No dinosaur currently known from body
fossils has a foot that could have easily made these prints.

        The prints are from the Early Maastrichtian of the Harebell Fm. in
Wyoming.  The paper will be in _Cretaceous Research_, hopefully within a
year.  Also, as a peculiar sidenote, some of the prints may have webbing
between the toes.

        Anyway, the prints demonstrate that at least some theropods _did_
reverse the "shrunken" nature of digit I that is seen as far back as the
Late Triassic.  I personally don't find it nearly as likely that this
animal -- or therizinosauroids -- are relics from the Triassic that have no
fossil record whatsoever until the Cretaceous as they are reversals of the
shrunken condition.  Not that I'm a big fan of evolutionary reversals, but
they are possible.  Hey, after all, if such reversals didn't occur, then
birds wouldn't have such a large digit I either, having been descended from
reduced-hallux theropods (contra your BCF theory, sorry).





Jerry D. Harris
Schuler Museum of Paleontology
Southern Methodist University
Box 750395
Dallas  TX  75275-0395
jdharris@lust.isem.smu.edu
        (Compuserve:  73132,3372)

---------/O\------*     --->|:|:|>     w___/^^^\--o

TITLE OF A REAL SCIENTIFIC PAPER:

"South American Animals and Their Lice"

---------/O\------*     --->|:|:|>     w___/^^^\--o