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Re: SVP DINO-PRESENTATIONS - Stegosaurus
I disagree with the way both Czerkas and Carpenter are restoring Stegosaurus
tail spike arrays, although both are correct in certain regards. Czerkas is
correct that the anterior pair of spikes was probably not horizontal, but
instead diverged at about 45 degrees. However, his showing the posterior
spikes at a similar orientation is incorrect. The end of the tail has a
little S-curve, and the spike bases are beveled, so the posterior spikes
pointed strongly backwards as Carpenter shows. This results in the effective
"pin-cushion" weapon moi illustrated in the 1987 Dinosaurs Past & Present Vol
II (which I still see on sale every once in awhile).
The two SVP presentations favoring no cheeks in ornithischians (and
therizinosaurs as well) ignored the reduction and enlargement of the lateral
maxillary and dentray foramina I noted in my JVP paper in 1984. This is also
observed in mammals, and suggests the replacement of thin lips feed by small
vessels and nerves in favor of thick cheeks fed by a few large ones. Where
may dinosaur cheek muscles have come from? I don't know, but then I do not
know where the muscles that close off croc nostrils came from either.
Entirely new muscles can be evolved.