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Re: DIGIT LOSS INQUIRY



George Olshevsky (Dinogeorge@aol.com) wrote:

<Not necessarily; there is some phalangeal loss in all those other
taxa (particularly the theropods, which are pretty much irrelevant to
Iguanodon). And Ouranosaurus may also have retained four V-manual
phalanges. So a primitive number of four V-manual phalanges for
Dinosauria cannot be excluded. Plus, these are manual digits, and I'm
more concerned with pedal digits here.>

  Manal digits? I thought the argument was about how "digits" could
not re-evolve, not pedal digits. But anyway ... given the number of
count in more basal animals aside from the Iguanodontia, as Mickey
points out, other dinosaurs do tend to reduce phalangeal count ...
so, curiously, with *Iguanodon* and *Ouranosaurus*, manal phalanges
from a basal condition _do_ increase in count. The same can be
applied to the pes.

  Besides, embryology indicates that even animals with three adult
digits still retain a fourth metacarpal as cartilage, which is
resorbed. Similarly, phalanges as cartilage caps may never ossify,
and an animal with five cartilage fourth digits phalanges can ossify
these bones separately from an ancestor who didn't, which may have
occured in several frogs. The case is not clear, and I cannot suggest
that what George says cannot happen, but the data says that it can go
both ways, but tends to point to serial reduction with successive
increase in some groups, so that increase can occur. Reversals do
seem to occur in nature....



=====
Jaime A. Headden

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

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