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Re: Biggest predators



At 08:53 PM 3/15/99 -0500, Patrick Norton wrote:
>Tom Holtz said:
>
>>_Deinocheirus_ is not much like these at all.  It's claws have a very low
>angle of curvature, they are VERY broad in cross-section, they do not show
>the typical theropod (indeed, basal dinosaurian) deflection of manual digit
>I.  Instead, they have the same  metacarpal proportions and shapes as
>ornithomimosaurs.<
>
>Is there any evidence that claws do not change allometrically (different
>shapes at different sizes) as do theropod teeth--particularly tyrannosaurid
>teeth?

Funny you should mention that... :-)

Actually, there seems to be very little allometric change in claw shape
among clades of theropods: _Utahraptor_ claws plot among the same field as
_Velociraptor_ claws, big allosaurs with little allosaurs, etc.

There are claws comparable to or larger than _Deinocheirus_' (_Baryonyx_,
_Suchomimus_, _Torvosaurus_, _Dryptosaurus_, etc.) which have greater
curvature, a more oval cross-section, and a tapered length: the more classic
"eagle-talon" like claw, presumably for piercing and holding. 

>>Whatever _Deinocheirus_ was doing, it was doing it much more like an
>ornithomimosaur than like allosaurs or dromaeosaurs. <
>
>And what precisely were ornithomimosaurs doing with those claws anyway?

Hooking and clamping.  Hooking and clamping *what*, I don't know: branches
seem a likely candidate, but catching up smaller animals would work, too.

Despite popular (and some techinical) descriptions to the contrary, there is
nothing raptorial about the claws of _Deinocheiurus_.  They are fat, poorly
curved, and not very tapered.  One of the most informative thing to do with
_Deinocheirus_ claws (on the off chance you happen to have access to casts,
which granted is a very rare thing) is to place one down next to a
_Torvosaurus_ or similar claw.  They are very different structures.

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