Bill Payne wrote:
A second question along this same line is whether forms which appear to
be transitional are truly so. The book _Of Pandas and People_ shows
silhouettes of three skulls: a Tasmanian wolf, a North American wolf, and
a dog. The cranial-cavity size increases as you go from the Tasmanian
wolf to the dog, suggesting a transitional relationship. However, we
know the Tasmanian wolf was a marsupial, while the other two are
placental mammals. Convergent evolution can produce forms which look
transitional but which we know are not, based upon soft-part anatomy,
which of course is rarely fossilized. Is this factor just generally
ignored by those inferring evolutionary relationships?
One issue that occurs to me about transitional fossils is that they are
just that, not long lived species. Almost by definition
transitional fossils will be rare (or even absent) in the record, because
there never will have been many of them. The
liklihood of any particular creature being fossilized is small enough, the
liklihood that the one that gets fossilized is the
actual ancestor of all following creatures is practically zero. So we
shouldn't be surprised that the transitions are hard
to follow. The amazing thing is that we can follow it at all.
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