randman writes:
is there any speciation event along this theorized chain that is documented in the fossil record, meaning the species prior and the species afterwards if shown?
Hi randman,
One problem with your request is that we can not necessarily make a "chain" of fossil animals that lead from one ancient extinct form to the modern day species. For any taxa, the fossil record is not complete; who knows how many generations pass between rare fossilisation events, and who knows whether fossil whale-like forms are a part of the chain, or side branches to it that ended up fizzling out?
However, if you are interested in looking at a good quality fossil record of a major evolutionary transition, you have chosen excellent subject matter in the whales. Fortunatley for us, there are a wide variety of apparently intermediate forms between quadrupedal mammals and non-legged modern whales. I can't post details including dated fossil photographs until I get home from the lab, because my whale material is all in my house (and I'm by no means an expert on cetacean evolution, I will need to look it all up in my notes).
But the general idea is as follows:
There are fossils available that show this entire transition, and they are dated sequentially. I'll post detailed stuff tomorrow.
Mick
added in edit: as far as I know, the dental information we can glean from fossils suggests a long period of semi-aquatic life; even the earlist protowhales with four legs appear to have lived in coastal estuaries and been good swimmers. There is a lot of behavioural evidence we can get from the fossil record, and the story is pretty complete. More tomorrow...
This message has been edited by mick, 08-03-2005 08:31 PM