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Re: A fundimental conundrum concerning gigantic theropods



Peter Buchholz wrote:

>If this were so, a fundimental question arises?  If bipedality is _so_
>unstable, why is it EVER "selected" for?  Even more telling is if big,
>running bipeds are _so_ unstable, why did at least four seperate
>theropod lineages independantly evolve gigantic sizes (Neoceratosaurs,
>Spinosaurs, Allosaurs and Tyrannosaurs) and be designed for running
>faster than 25 km/h?  If it was _so_ bad, the very first giant
>Abelosaur should have fallen flat on his/her face and died.
>
>This obviously didn't happen.  It seems to me, that in the
>evolutionary longrun, being a gigantic, fast predator far outweighs
>the possible detriment of falling on its face.  The evidense: at least
>four seperate theropod lineages that were seemingly fast animals and
>truely gigantic.

Now, wait just a minute.  Tyrannosaurids alone of the big theropods show
abundant cursorial adaptations.  The others had shorter, squatter legs,
non-pinched fatter metatarsi, larger fibulae, smaller ascending processes of
the astragalus, etc.

Further, the non-tyrannosaurids dominated in environments where the most
common large herbivores were stegosaurs and sauropods, hardly the fastest of
dinosaurs.

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."
-- Tim the Enchanter, "Monty Python and the Holy Grail"
---------- subtitle --[Monty Python ik den Holy Grailen]

"Tim?!?  They called me TIM?!?!"
-- Tom the Paleontologist, on seeing "The Ultimate Guide to T. rex" :-)