Deinocheirus, and spinosaur systematics

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

At 01:00 AM 11/13/98 -0500, Chris Srnka wrote:
>I haven't seen the actual specimen for _Deinocheirus mirificus_, and
>I've only seen a few photos and drawings of the same, but the sight of
>_Suchomimus tenerensis_ reminded me of the famous forelimbs of
>_Deinocheirus_. Is there any speculation that _Deinocheirus_ was an
>advanced Spinosaur? Just wondering, and forgive my ignorance.
>-Chris Srnka

The forelimbs of _Deinocheirus_ and spinosaurids are amazingly different.

_Deinocheirus_ has very long and slender arms, metacarpals all the same
length, unguals all the same size, which have only moderate curvature and
are very thick in cross-section throughout their length.

Spinosaurids, like the new _Suchomimus_, have very short and stocky arms,
thumb claws which are dramatically larger than the other unguals, unguals
with greater angles of curvature, a tapering shaft, and more oval slender
cross-section (like that of a carnosaur or _Torvosaurus_ claw).

Also in the _Suchomimus_ paper:
Now (and you must understand how hard it was to keep from presenting this
the last few weeks during the spinosaur discussions on the list...) we
finally have a cladistic analysis of the Spinosauridae.  Using Neotetanurae
and Torvosauridae (=_Eustreptospondylus_ + _Torvosaurus_) as outgroups,
Sereno's Baker's Dozen found the following tree:

Spinosauridae
   Baryonychinae
     _Suchomimus_
     _Baryonyx_
   Spinosaurinae
     _Irritator_ (incl. _Angaturama_)
     _Spinosaurus_

Baryonychines are characterized by (among other traits) the increased number
(and decreased size) of dentary teeth (about 30) and a blade-shaped ventral
keel to the anterior dorsal centra.  Spinosaurines are characterized by very
straight teeth lacking serrations (and lack the derived increase in dentary
tooth number).

Sereno et omnia refer the type and most referred material of _Spinosaurus
maroccanus_ to _S. aegyptiacus_, and cannot distinguish _Cristatusaurus_
from _Baryonyx_ on anatomical grounds.

Oh, and there now is a morphological feature by which spinosaur teeth can be
distinguished from crocodilian teeth: the enamel of spinosaurs have a
characteristic wrinkled texture (Milner has described this in some of her
talks).

Oh, and for measurement freaks, the femur of _Suchomimus_ is 1075 mm,
putting it into _Daspletosaurus_ and _Gorgosaurus_ (and young
_Tyrannosaurus_) range.

More later,

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