[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Quo vadis, T. rex?

In a message dated 96-02-01 17:27:36 EST, pharrinj@PLU.edu (Nicholas J.
Pharris) writes:

>Why are you suggesting this?  Does it have anything to do with the 
>didactyl manus in that genus? (which, incidentally, has a reconsturcted 
>phalangial formula of 2,3,3,0,0, more "derived" than any tyrannosaur).  
>Didactyly is pretty easy to develop in parallel.

(1) The phalangeal formula of _C._ AS PRESERVED is 2,2,0,0,0 (only two
digits: not 2,3,3,0,0), but if one and the same phalanx were missing from
both hands (not unlikely), the correct formula would be identical to that of
tyrannosaurids: 2,3,0,0,0. I think it is very _unlikely_ that _all eight
phalanges_ from the third digits of both hands--if such digits were present
in life--would depart, but leaving almost all of the phalanges of digits I
and II with the specimen.

(2) Didactyly is not at all easily developed in parallel. Practically all
theropods had three or four manual digits, even those with absurdly reduced
forelimbs, such as _Carnotaurus_. _Only_ tyrannosaurians had didactyl
forelimbs (and I include _Compsognathus_ as the earliest, most primitive
known member of that suborder). You should decouple the ideas of "forelimb
reduction" and "digit-count lowering" from each other; they do not go "hand
in hand" (arghh--no pun intended).

The progressive reduction in manual digit count seen in theropods is the
result of some pretty painstaking evolution of the wing (BCF theory here;
ignore at your peril). Digits do not just drop away willy-nilly without a