[asa] dinosaur evolution

Nature has an article about the evolution of dinosaur fingers that
helps clear up a problem, also illustrating the dangers of
overcommitment to a position.

Most carnivorous dinosaurs, including those thought to be closest to
birds, have three fingers. They have generally been thought to be 1-3
(i.e., thumb, index, middle).

Embryological study, involving some of the prominent "birds are
cousins of dinosaurs, not descendants of them" folks, suggested that
birds have fingers 2-4 (the middle three). This was often just
dismissed by the "birds are dinosaurs" crowd.

The new article presents strong evidence from a four-fingered fossil
that the dinosaurs in question actually retain 2-4, but with some
modifications that resemble 1-3 instead.

I would also point out that my son (almost 4 2/3 years) preferred
using fingers 2-4 in pretending to be a dinosaur species with three
fingers well before this article appeared.

A Jurassic ceratosaur from China helps clarify avian digital
homologies pp940-944
The bird hand is thought to derive from the second, third and fourth
digits of an ancestral five-digit hand. However, the three-fingered
hand of theropod dinosaurs, which are the closest extinct relatives
of birds, are thought to derive from the first, second and third
digits. The discovery of a small, primitive herbivorous theropod from
the Jurassic period of China with a stub of the first digit alongside
more developed second, third and fourth digits, sheds light on this
problem.
Xing Xu et al.
doi:10.1038/nature08124
Abstract: http://links.ealert.nature.com/ctt?kn=159&m=33425712&r=MjA1NjgxMjU1MgS2&b=2&j=NTE2MDQ0NTYS1&mt=1&rt=0
Article: http://links.ealert.nature.com/ctt?kn=168&m=33425712&r=MjA1NjgxMjU1MgS2&b=2&j=NTE2MDQ0NTYS1&mt=1&rt=0

-- 
Dr. David Campbell
425 Scientific Collections
University of Alabama
"I think of my happy condition, surrounded by acres of clams"
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