Tyranno Hands - Wings and Such

[Tony Thulborn <paswamp@mailbox.uq.oz.au>]

In response to Michel Chartier's request for a summary (May 22).....
        The paper is based on evidence of small thecodontian 
(?ornithosuchian) and theropod tracks of Late Triassic age, from Europe 
and north-eastern United States.  All these tracks, made by small animals 
travelling on all fours, include reasonably well preserved prints of the 
manus.  I ordered them into a transformation series, which also happens 
to correspond with their stratigraphic sequence.
        These ichnotaxa are: Sphingopus ferox... Coelurosaurichnus 
perriauxi..  Atreipus acadianus... Atreipus milfordensis & other 
ichnospp. (e.g. A. metzneri).  This series shows progressive reduction in 
number of digits in manus, from pentadactyl (S. ferox and C. perriauxi), 
through tetradactyl (A. acadianus) to tridactyl (A. milfordensis et 
al.).  First digit 5 (minimus) disappears, to be followed by digit 1 
(pollex).  The other three digits, numbers 2-3-4, retain essentially 
unchanging topography throughout.  In short, it looks as if the typical 
tridactyl manus of theropods comprises digits 2-3-4 and originated 
through loss of digit 5 followed by loss of digit 1.  Further reduction 
at the lateral side (loss of digit 4) would leave the didactyl manus of 
tyrannosaurs, comprising digits 2 and 3.
        I doubt that this story will change anyone's opinions (A) because 
it's based on footprints, not "good" skeletal evidence; (B) because 
there's some uncertainty over the identity of the Sphingopus trackmaker 
(though I follow Georges Demathieu in regarding it as the track of an 
ornithosuchian); (C) because Paul Olsen and others (?) insist that 
Atreipus comprises tracks of ornithopods and not, as I've suggested, of 
theropods; and (D) because it's presented as an old-fashioned and 
heartwarming transformation series, and not as a sterile cladogram 
(though it could readily be converted into such).
        When I say that "few" of us accept theropod/avian digits as 
2-3-4, I may be exaggerating.  There's me... and... er...um.  Oh dear.
Back to the swamp.