RE: Tyrannosaur hunter-gatherers?

["Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>]

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> David Marjanovic
>
> > Yeah, they would have had longer legs, but their femur/tibia+Mt3 ratio
> > increases with age.  If you want to run fast, you'll also want your
> > femur/tibia+Mt3 ratio to be as small as possible.  This isn't
> the case for
> > large adult tyrannosaurids.
>
> AFAIK that ratio is also bigger for adult ornithomimids than for juvenile
> ones... it's just size-related and apparently predictable from elastic
> similarity (see the speed chapter in PDW). Aren't their ratios
> still smaller
> than those of allosauroids of the same sizes?

For the answer to this and other related questions, see:
Holtz, T.R., Jr. 1995. The arctometatarsalian pes, an unusual structure of
the metatarsus of Cretaceous Theropoda (Dinosauria: Saurischia). Journal of
Vertebrate Paleontology 14: 480-519.

and

Farlow, J.O., Stephen M. Gatesy, T.R. Holtz, Jr., J.R. Hutchinson & J.M.
Robinson. 2000. Theropod locomotion. American Zoologist 40:640-663.
(The latter available online at
http://www.bioone.org/bioone/?request=get-document&issn=0003-1569&volume=040
&issue=04&page=0640; see figure 4).

In brief, though:
In non-avian theropods, the relative length of the tibia and the relative
length of the metatarsus decrease as femur length increases.  This is true
across taxa and through ontogeny.


Most of them fall along one trend, but ornithomimosaurs, Elaphrosaurus, and
tyrannosauroids (and a few others) fall along a trend with a similar slope
but a higher y-intercept (i.e., the same slope moved up slightly).  The net
result is that for a given femur size, ornithomimosaurs and tyrannosauroids
will have a longer tibia and a longer metatarsus than other theropods.  Or,
to think of it in a different way, a particular MtIII/F or T/F or (MtIII +
T)/F ratio will occur at a larger body size in tyrannosauroids and
ornithomimosaurs than in other groups of theropods.

Now, be warned: as Hutchinson and others show, there is a lot more to
absolute speed and to cursoriality than just limb segment proportions!!
Still, the observation remains true that all tyrannosauroids and
ornithomimosaurs have more elongate distal limb elements than those of other
large theropods of the same body size.  Furthermore, MtIII/F values are
*much* higher in tyrannosauroids than in hadrosaurids of the same femur
length, and T/F are higher (but to a lesser degree) in tyrannosauroids than
in hadros of the same femur length.

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796