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Re: Dinosaur's hopping?



>   According to everything I've read, and according to the professor who
>taught my dino class this past spring, the first dinosaur was an obligate
>biped.  Additionally, if I remember my readings correctly, the
>thecodonts/protodinosaurs, the immediate ancestors of the dinosaurs, were
>also obligate bipeds.

        Well, as far as we _know_ (with the likes of _Eoraptor_ and
_Herrerasaurus_) the earliest KNOWN dinosaurs were bipeds.  Some of the
suspected "protodinosaurs," such as _Lagosuchus_, weren't obligate bipeds,
but were probably facultative either bipedally or quadrupedally.  Many of
the "thecodonts" (by no means all:  no one's ever suggested that phytosaurs
or aetosaurs, for example, were bipeds!) were probably at least facultative
bipeds, including ornithosuchids, rauisuchids, poposaurids, and other
"lagosuchids."

>   That would seem to mean that bipedality in dinosaurs evolved ONCE, with
>quadrupedality separately evolving in each of the Dinosaurian suborders later.

        Quadrupedality did indeed evolve secondarily in various dinosaur
groups, but as it appears that rauisuchids and poposaurids probably didn't
have much to do with dinosaur origins (although there's a great deal of
convergent evolution amongst the groups!), we can't say bipedality only
evolved _once_.

        Gee...and wouldn't it be interesting to see what would happen if
some species of bird reverted to quadrupedality (tree-climbing baby
hoatzins notwithstanding)!  8-)



Jerry D. Harris
Denver Museum of Natural History
2001 Colorado Blvd.
Denver, CO  80205
(303) 370-6403
Internet:  jdharris@teal.csn.net
CompuServe:  73132,3372

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