GRACILITY AND SPEED OF T. rex

by Thomas R. Holtz, Jr.

>cheetahs, and T rexs, do you consider lions, being a very robust
>animal, like cheetahs, and not like T rex, also a very robust animal.
>T rexs certainly aren't gracile in any way. Cheetahs are very

Sorry, Betty,but T. rex is very gracile. In terms of tibia/femur and metatarsus/femur ratio, Tyrannosaurus is MORE gracile than Deinonychus!! It is also more gracile than any other 5 tonne critter, Mesozoic or Cenozoic!

Tyrannosaurus does not LOOK very gracile, for two reasons: 1) at such a large size, gracile limb proportions look bulky. However, compare the hindlimb of Tyrannosaurus with an elephant, a rhino, a Triceratops, even an Edmontosaurus. You will see that the T. rex legs are more slender and have relatively longer tibiae and metatarsi. 2) The most famous T. rex mount in the world, AMNH 5027, has the wrong legs!! Since this specimen (a gracile morph) lacked hindlimbs, Osborn et al. added casts of the legs of the type (now at the Carnegie). The type is the robust morph, and a larger individual!

Furthermore, the feet of the type (and thus the AMNH mount, and thus many many copies, drawings, models, etc., etc.) were and remain(!) incorrectly restored. Not realizing that tyrannosaurids had ornithomimid-like feet, Osborn et al. reconstructed the feet of T. rex after Allosaurus, giving the mount a much broader foot than it should have.

>gracile. They have flexible spines so that in the full gallop their
>spines ripple like a trampoline. I don't picture T rex's spine doing
>anything so undignified during a run. I can see (perhaps) something
>smaller and more elegant of form like VelocIraptor or Deinonychus
>developing along the lines of a speedster like the cheetah, but not
>ol' brick T rex. He's built like a truck, not a Ferrari. Perhaps
>even Allosaurus fragilus might be considered to be a speedier design,
>but T rex?

Tyrannosaurus limb proportions are more gracile than Allosaurus fragilis. The smaller tyrannosaurids were even more gracile, and the smallest had the same limb proportions to the largest ornithomimids: measurement for measurement, the legs of Alectrosaurus and Gallimimus are identical!

Dromaeosaurids have about the least gracile limb proportions of any nonavian theropod (only therizinosauroids had worse!). Crichton aside, dromaeosaurids were probably not very fast runners relative to tyrannosaurids, ornithomimids, etc. Instead, they were probably cat-like ambush predators, relying on short bursts of high speed, quick turns, and an all-out attack with all four legs and the mouth, too!

>I think your point about tendons is valid, but I believe T rex's
>adaptations were more for being the biggest kid on the block, not the
>fastest.

If we can use functional morphology as a guide, tyrannosaurids were faster than any other group of large theropod (allosauroid, megalosauroid, neoceratosaur). This may not mean that they were fast as racehorses, but they were adapted to (for a large animal) high speed.

>(and what with all the fused tendons along most therapods' tails, you
>don't see the completely supple spine like in a cheetah, anyways.
>Therapods spines seem to have been reinforced to prevent exactly that
>kind of movement.)

Actually, cheetah tails are held about as rigid as they can be, except at the base. Cheetah's and other big cats use their tails as dynamic
stabilizers, to turn on a dime at high speed. This is exactly the condition we find in the Dromaeosauridae.