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Re: Birds, dinosaurs, and digit 1



Now, this is what I call an elegant post with evolutionary sense. Please
pay attention!

Dinogeorge wrote:
> note that there were
>many theropods with four-fingered hands (ceratosaurians) from which modern
>birds might have descended, eliminating digit I and retaining digits II-IV.
>But the correspondence of phalangial counts >and shapes< in maniraptoran
>dinosaurs to those in _Archaeopteryx_, not to mention the remainder of the
>skeletal anatomy, pretty much nails down the close relationship between those
>two forms and strongly suggests that avian wing digits are I-III. If II-IV in
>modern birds is correct, then _Archaeopteryx_, despite its feathers, is only
>a distant relative of modern birds and not close to modern-bird ancestry.
>That is, there would have to be at least two distinctly different avian wing
>types in the Mesozoic: those with digits II-IV and those with digits I-III.
>Maybe this difference also correlates with ornithurans (II-IV) and
>enantiornithans (I-III)? Maybe _Protoavis_ (more modern-looking than
>_Archaeopteryx_, according to Chatterjee) represents a primitive ornithuran,
>whereas the commonest Cretaceous birds were all enantiornithan? Lots of
>different ways not to throw the baby out with the bath water.

And I still think they are misinterpreting embryology. But it is
fascinating to think of a multiple, convergent origin of birds from
different types of dinosaurs (or dinosaurs from different kinds of birds,
however you like it). That clearly gives Dinosauria (or Aves) a role that
is somewhat similar to what  Homo ergaster or Homo erectus  is to the
different kinds of Homo sapiens.

Luis Rey

Visit my Website on http://www.ndirect.co.uk/~luisrey