Re: More on Digit Loss in Theropods

["Jaime A. Headden" <qilongia@yahoo.com>]

  With the suggestion that larger animals might increase digits is a 
suggestive, but not complete,
theory. In suggestion that bigger dogs display more toes, and that this does 
not appear correlated
to cats, it looks promising until the suggestion that maybe the cats were doing 
something wierd to
change it. A complete hypothesis suggests that maybe the _dogs_ were doing 
something wierd. David
Marjanovic makes some note of other large animals, but I would like to remind 
the list (most of
whom I'm sure don't need it) and David that those mammals that are large but 
have few toes are
typically cursorial. In cursorial animals, such as the horse (and the giraffe) 
and ostrich and
some cranes, the digits are reduced to between two and one. The more cursorial, 
the fewer toes.
hence, cursorial theropods like ornithomimids had only three absolute toes, 
even though all
theropods had only three effective toes with the possible exclusion of 
segnosaurs (I am not sure
the hallux actually participates in locomotion, as only the unguo-phalangeal 
joint can touch the
ground).

  There is also a possible correlation to a quadrupedal exaptation pressure 
affecting digit loss
in non-cursors and non-aquatic mammals (cursors and aquatic mammals have 
different exaptation
pressures affecting digit shape and count).


=====
Jaime A. Headden

  Aaaaaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhr-gen-ti-na
  Where the Wind Comes Sweeping Down the Pampas!!!!

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