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Re: Biggest predators



At 12:52 PM 3/18/99 +0100, Berislav Krzic (and Dinogeorge before him) wrote:

>>Absolutely correct. Also, relatively longer, slenderer skull in
>Tarbosaurus,
>>with more maxillary and dentary teeth (e.g., dentary count 16 versus 13 in
>T.
>>rex) that are somewhat smaller and slenderer than the "rail spike" teeth of
>T.
>>rex, and skull much narrower behind, with occipital condyle visible in
>dorsal
>>view (so skull is held more horizontally than in T. rex; forwardly declined
>>skull is part of the stereo suite of characters of T. rex skull). In
>addition
>>to generally larger size (est total length 14 meters vs. 8-10 for
>>Tarbosaurus), Jenghizkhan has relatively taller dorsal vertebrae with the
>>tallest neural spines (though still pretty short when compared with
>something
>>like Acrocanthosaurus) in Tyrannosaurinae.

I agree with the above.  However, differences do not mean that they aren't
closely related.  Also, do not be too wedded to the idea of the utility of
tooth count to distinguish different taxa of tyrannosaurids: there is a lot
of in-taxon variablity (some of which is ontogenetic).

Speaking of variability, keep in mind the variablity within North American
_T. rex_ specimens in terms of cranial ornamentation, proportions, tooth
count, etc.

Also, for those concerned with the preponderence of "mid-sized" Asian
tyrannosaurs relative to the rare big _T. bataar_ specimens, we have the
opposite case with _Tyrannosaurus_.  Very large individuals are relatively
common (for a large theropod...), but we have very little in the way of
small individuals.  Who knows, maybe subadult and adult large tyrannosaurids
lived in different environments, and the Nemegt samples the preference for
subadults while the Lance/Hell Creek samples the old-folks home...  (Okay,
not a real serious idea, but consistent with the observations).

>All tarbosaurini (Tarbosaurus
>and
>>Maleevosaurus; unknown in Jenghizkhan) had relatively the smallest
>forelimbs
>>of all tyrannosaurines, probably a synapomorphy for the tribe.

It may well be, although the taxon it is a synapomorphy for could equally
well be a single Asian species.

>Can we agree then, that Deinocheirus wasn't a match for Jenghizkhan (ex
>Tarbosaurus, ex Tyrannosaurus?) even with its huge claws and the best it
>could have done was to run like hell on its (probably) relatively longer
>legs?

Why on earth would _Deinocheirus_ have relatively longer legs?!?!
Ornithomimids and tyrannosaurids plot along the same trend of distal limb
length-to-femur length (Holtz, 1995 and elsewhere).  If _Deinocheirus_ is an
ornithomimosaur, it should have the same limb proportions of an
equivalent-sized tyrannosaurid.

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