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Re: pterosaurs, bats, flying theropods



Original Message by Jaime A. Headden
Tuesday, 24 December 2002 04:10

>   Hey, it happened to the whales in the Eocene, and that's with Paleocene
> and Eocene ancestors that are reasonably known.

Paleocene ancestors for whales? Some sort of "*Diacodexis*"? Or do you mean 
Arctocyonia?

> Bats may very well have their earliest ancestors in the Paleocene,
> and very bat-like archontans like colugos (Dermoptera) exist that can be
> purported ancestors with little change.

Little morphological change perhaps. But I don't know a molecular tree which 
has found Chiro- and Dermoptera together. The latter comes out next to 
Primates as usual, together with Scandentia they form a pretty normal 
Euarchonta, and this is the sistergroup to Glires, whereas morphologically 
Lagomorpha alone, sometimes with the purely African Macroscelidia, tends to 
show up in this place. (The latter jump which produces the similarities to 
rabbits, AFAIK.)

> Most molecular dates do not take into account the
> possibility of Eldredge and Gould's PE, for example, or that gene
> evolution may occur at different rates with constraints at different times
> in a single lineage.

It is possible to find and acknowledge different rates in different lineages. 
It is AFAIK still not possible to find and acknowledge different rates within 
the same lineage (I recently did some literature research about that for 
university). In a catastrophic mass extinction lots of genetic bottlenecks 
are expected; small population sizes mean that mutations can become fixed in 
the gene pool much faster than usual -- faster molecular evolution occurs, 
and AFAIK _all_ molecular datings assume a priori that this never happens.

Nevertheless, it is possible to find Paleocene divergence dates for 
divergences within the big placental clades. I cited the paper. Download it 
for free, and read it. :-)

Merry Xmas, everyone :-)