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The Hand of *Mononykus* [was Re: ... *Titanis*]



<<Chandler, R.M. 1994. The wing of *Titanis walleri*
(Aves:Phorusrhacidae) from the late Blancan of
Florida. _Bulletin of the Florida Museum of Natural
History Biological Sciences_ 36 (6): 175-180.>>

Larry Febo wrote:

<The carpometacarpus seems "locked" in straight line
with the radius, ulna. This seems also the pose most
represented in Mononychus (is Mono`s wrist also
"non-bendable"?). A solid humerous (as opposed to
pneumaticized) is said to have evolved through active
use of the forearms for fending off struggling
prey(which were dispatched mainly by use of it`s large
beak). Did Mononychus have a "solid humerous"?>

  The humerus of *Mononykus* articulates the forearm
in such a way as to limit completely the folding
function of the arm seen in other maniraptoriforms; as
an avialian (Perle et al., 1993, 1994; Chiappe et al.,
1996), this is a derived reversal of several related
features, and is still a derived reversal if it was
less closely related to birds (Sereno, 1999),though
the number is slightly less. The distal articular
surfaces of the humerus are oriented only cranially,
and the ulna and radius are very tightly appressed to
each other, limiting slide and twisting
(pronation/supination). Furthermore, the "wrist"
region is very nearly locked, so that the only motion
apparently possible was flexion and very little
extension (see Perle et al., 1994).

  There does not seem to be a foramen in the humerus
to indicate it is pneumatized in any way, as in birds.
This really doesn't say much, except that the humerus
was more dense than relative-sized birds or their
humeri. It increases the extent to which tension can
be exterted on the bone and with counter-torsion
effects, etc. Laminae on the bone show where divisions
of the muscles and attachements of same would have
existed to increase strength. Similarly, the
deltopectoral crest is large and set from the head,
increasing leverage from, say, dromaeosaurids or even
*Archaeopteryx*. The bone in lateral and proximal
aspect resembles that of pterosaurs, and possibly for
the same reasons (see Perle et al., 1994).

Refs:

  Perle A.; Norell, M.A.; Chiappe, L.M.; and Clark,
J.M. 1993. Flightless birds from the Cretaceous of
Mongolia. _Nature_ 362: 623-626.

  Perle A.; Chiappe, L.M.; Barsbold R.; Clark, J.M.;
and Norell, M.A. 1993. Skeletal morphology of
*Mononykus olecranus* (Theropoda: Avialae) from the
Late Cretaceous of Mongolia. _American Museum
Novitates_ 3105: 29pp.

  Chiappe, L.M.; Norell, M.A.; and Clark, J.M. 1996.
Phylogenetic position of _Mononykus_ (Aves:
Alvarezsauridae) from the Late Cretaceous of the Gobi
Desert. _Memoirs of the Queensland Museum_ 39 (3):
557-582.

  Sereno, P.C. 1999. The evolution of dinosaurs.
_Science_ 284: 2137-2147. [w/ supp. info]

=====
Jaime "James" A. Headden

  Dinosaurs are horrible, terrible creatures! Even the
  fluffy ones, the snuggle-up-at-night-with ones. You think
  they're fun and sweet, but watch out for that stray tail
  spike! Down, gaston, down, boy! No, not on top of Momma!

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