Tyranno hands (was Re: Wings and Such)

[Tom Holtz <tholtz@geochange.er.usgs.gov>]

>   On an aside, which fingers are left on T Rex?  He's got 2 on each hand,
>but which 2?  Are they fused carpals/phalanges, or lost carpals/phalanges?

Most theropod workers would agree it is digits I and II (the thumb and the
index finger), given what we know of theropod hand evolution (from
Herrerasaurus on).  The metacarpals and phalages of digits III on were
lost, V first (none above Herrerasaurus), then IV (all tetanurines but
Sinraptor and maybe Composgnathus lack metatarsal IV), then II (in the
ancestors of the tyrannosaurids).

The question of carpals - only a few tyrannosaurid specimens have been
found with carpals in position.  It is difficult to tell the homologies of
tyrannosaurid and ornithomimosaur carpals, since both are degenerate from
the original, well-formed, faceted condition.

                                
Thomas R. Holtz, Jr.                                   
tholtz@geochange.er.usgs.gov
Vertebrate Paleontologist in Exile                  Phone:      703-648-5280
U.S. Geological Survey                                FAX:      703-648-5420
Branch of Paleontology & Stratigraphy
MS 970 National Center
Reston, VA  22092
U.S.A.