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Re: Phytodinosauria status

George Olshevsky (Dinogeorge@aol.com) wrote:

<Something like the wings of dinobirds as they repeatedly
evolved into giant, cursorial theropods, eh?>

  Sort of. Any un-used elements will cease to operate in a
functional state; these states are no longer selected for; ergo,
the theory stands that they will be lost. This trend is the
major interpretation in loss of digits in tyrannosaurids and
tetanurans broadly.

  However, the basal carnosaur form had four metacarpals, as
suggested by *Sinraptor*; three metacarpals are recovered only
for *Allosaurus* and *Acrocanthosaurus*.

  Loss of the metacarpals appears to be functional, in that the
manus has become developed towards acqusition. This is as
telling as the prescence of only three metacarpals (?; not
ideally preserved, I guess I'm predicting it) in hands-on
predators like spinosaurids. That Tetanurans have forms with
four metacarpals (*Coelurus*) suggests that digit reduction has
two trends: very large size; and hands-on predation. Both are
present in carnosaurs and presumably in spinosaurids.
Tyrannosaurids reduce the forelimbs, theoretically, to provide
balance shift to the skull so that the forequarters are not
overbalanced with the heads-on approach they enjoy. Thus only
main-stream coelurosaurs and the paradigm noticed by Gauthier
and Holtz seems to fit _generally_. Those big 'uns are monkeys
in the works.

Jaime A. Headden

  Where the Wind Comes Sweeping Down the Pampas!!!!

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