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Some of you (particularly Norm King) were interested in knowing whether
there are maniraptoran autapomorphies present in the hands of tyrannosaurs.
Well, I seem to have found a pretty good one.
Much has been made of the fact that the proximal phalanges of the third
finger are hypershortened in maniraptorans. Less well-known is the fact
that the same is true of the proximal phalanx of digit two.
Among the theropods whose manus I could get a clear look at,
_Allosaurus_, _Sinraptor_, _Ornitholestes_, _Chirostenotes_, _Elmisaurus_,
and _Alxasaurus_ have phalanges II-1 and II-2 of roughly equal length.
_Deinonychus_, _Oviraptor_, and _Archaeopteryx_ have phalanx II-1 about
two-thirds the length of II-2, although _Ingenia_, in typically weird
fashion, has phalanx II-1 slightly *longer* than II-2.
Finally, _Tyrannosaurus bataar_, _Gorgosaurus_, _Harpymimus_,
_Struthiomimus_, _Ornithomimus_, _Gallimimus_, and _Sinornithoides_ have
phalanx II-1 from slightly under half to somewhat over half the length of
So tyrannosaurs share a derived form of manual digit II, along with many
other characters, with ornithomimosaurs and troodonts.
How much, BTW, is known of the manus of _Baryonyx_?
(I also checked out the palate of _T. rex_ and looked for maniraptoran
characters. A lot of the palate looks much like that of _Dromaeosaurus_,
particularly the vomers and ectopterygoids--certainly much more like a
maniraptor than like _Allosaurus_.)
This brings me to my thoughts on the reconstructed manus of
_Compsognathus_, which I scrutinized for a while last night. My thoughts
are this: pretty screwy. As reconstructed, metacarpal I is the longest
and most robust of the three. The *only* theropod in which this is
definitely the case is _Ornithomimus velox_. Not impossible, but suspicious.
"Metacarpal I" is also shown with a wide base and narrowing from the
medial side. I can find no other theropod manus structured in this
manner, but this bone *is* quite reminiscent of metacarpal *II* in
Finally, as reconstructed, phalanx I-1 is about half the length of
metacarpal I. No theropod thumb, none, is structured in this manner.
My hypothesis is that Ostrom got manual digits I and II confused: that
the digit reconstructed as II is, in fact, the thumb; and that the digit
reconstructed as I consists of the metacarpal and proximal phalanx of
digit II. The medial phalanx of digit II is, apparently, missing.
More detailed analysis of the specimen will be necessary to confirm or
refute this hypothesis.
The presence of such a short phalanx in the manus of _Compsognathus_
strongly suggests that this little animal had the hypershortened phalanx
II-1 characteristic of the Arctometatarsalia; and this may, along with
cranial, pedal, and pelvic characters, lend support to the hypothesis that this
animal is a basal arctometatarsalian.
The ankle of the type looks pretty beat up. Anyone who has actually
examined the specimen: is it possible that metatarsals II and IV do
touch on the dorsal surface of the pes?
Just a thought.
Pacific Lutheran University
Tacoma, WA 98447
"If you can't convince them, confuse them." -- Harry S. Truman