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Re: Re-emergence of lost features.
> One may wonder whether the genetic information to redisplay an old
>feature >can still be there after tens of millions of years - after all,
>unexpressed >genetic material undergoes much faster mutation than
>expressed stuff which is >subject to evolutionary honing.
Atavistic features within species are actually not that uncommon - horses
with multiple digits on the feet are one prominent example.
As for the return of "lost features," one of my favorite examples involves
the hylid frog Gastrotheca, which has lower dentition. No other frog has
lower teeth. Hylids are very derived frogs, and Gastrotheca is a very
derived hylid - we could either posit a great many multiple losses, or a
Moreover, IF the argument that birds have digits 2-3-4 in the wings is
correct (and I seriously doubt that it is), then this is a similar case -
the fourth digit would have been regained through a reorientation of the
primary axis of digital development.
> Are any examples of normal-winged birds with throw-back clawed hands
You mean like the modern hoatzin, which loses the claws before maturity?
>And why did the phorusrhacoids lose out to the early carnivorous mammals
>when a similar design survived for so long before?
Phorusrhacoids spent most of their history in South America prior to the
appearance of large-bodied marsupial predators. The only other competing
terrestrial predators were "sebecoid" crocodyliforms. Their appearance in
North America was relatively recent (Pleistocene).
Christopher Brochu, Ph.D.
Postdoctoral Research Scientist
Department of Geology
Field Museum of Natural History
Lake Shore Drive at Roosevelt Road
Chicago, IL 60605 USA
phone: 312-922-9410, ext. 469