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Re: T-rex leg length & walking



>I'd like some clarification regarding the issue of rex's leg length as
>mentioned in The Ultimate T-rex. First, how is it that 2 paleontologists
>(names forgotten, Horner v Currie?) can arrive at 2 different conclusions
>regarding bone length? Were they looking at the same specimen? Could
>differences have something to do with growth/age of specimen? If the
>thigh and shin are the same length, does that mean rex could both run and
>walk? Second, how can walking be derived? Can't walking simply be seen as
>slow running? Derived from what?

Horner can say what he said by totally ignoring the copy of my Journal of
Vert. Paleo. paper (JVP 14:480-519) that I shoved in his hand some time ago...
:-(

Quite frankly, if they had let me have a go at it, I could show you where
Horner was wrong in the most graphic of ways: graphics!

Tyrannosaurids and other pinched-footed theropods have proportionately
elongated distal limb elements (shins and feet).  When compared to other
theropods of the same size, a tyrannosaurid or ornithomimid or troodontid
have much longer legs than the other forms.  In fact, MOST tyrannosaurids
have tibiae which are longer than their femora, whereas almost all
allosaurids have longer tibiae than femora.  Heck, even large dromaeosaurids
have longer tibiae then femora, so that isn't a tyrannosaurid feature at all
as implied by Horner.

More to the point, what was ignored was allometry: the fact that different
parts of the body change relative proportions with different sizes.  Most
theropods fall within one of two allometric tracks.  Typical theropods
(ceratosaurs, allosaurids, basal coleurosaurs, etc.) follow one line, while
_Elaphrosaurus_ (the ornithomimid mimic) and pinched-footed coelurosaurs
follow a different track. In both cases, the femur becomes relatively longer
and the tibia and metatarsus relatively shorter as size increases, but the
long-legged beasties cross the femur length = tibia length at a much larger
body size (way up among the biggest tyrannosaurids).

Also, what was ignored by Horner but properly stated by Currie is the fact
that tyrannosaurids have MUCH more elongate limb proportions than the
relatively stumpy-legged potential prey items: hadrosaurids and
ceratopsids.  Tyrannosaurids didn't have to be faster than race horses: they
just had to be faster than duckbills and horned dinosaurs.  And, based on
limb proportions at least, they probably were.

Man, am I angry that they cut my scenes, or what?  :-)

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661

"There are some who call me...  Tim."