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Re: Stego/Ankylo limbs
At 03:03 PM 1/30/96 -0500, Dinogeorge@aol.com wrote:
>Since ceratopians were secondarily quadrupedal (the ancestral ceratopians
>were small bipedal marginocephalians and psittacosaurs), there is no reason
>to expect their graviportal forelimbs to have had a pose as fully erect as
>their hind limbs, which had been primitively erect (a dinosaurian apomorphy)
>for about 150 million years. Indeed, because the large, graviportal
>ceratopians had evolved quite rapidly during essentially the second half of
>the Late Cretaceous (about 20 million years altogether), one would not expect
>much in the way of a fully erect pose--the result of lengthy evolution--from
>the formerly grasping forelimbs. The forelimbs became suborned in a "fast and
>dirty" way to holding up the animals' forequarters, letting the "evolutionary
>chips" fall where they may. Perhaps, had there been no terminal Cretaceous
>extinction event, the forelimbs of ceratopians would eventually have trended
>toward a more fully erect pose, but now we'll never know.
The last time I checked, the largest skull attributed to a
terrestrial animal belonged to a ceratopian -- over seven feet in length.
When alive, the head of this animal weighed thousands of pounds moving the
center of gravity for the animal forward. If the animal had sprawling
forelimbs this would move the center of gravity even further toward the head
and thus increase the already monumental load on the forelimbs.
Additionally, a sprawling posture together with such a huge load would place
enormous stress on the elbow, shoulder and wrists, as well as being far less
energy efficient than an erect stance -- if you don't believe me drop down
and do push-ups. A herd of Triceratops with sprawling forelimbs would be a
miserable, arthritic bunch barely mobile.