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Re: No Cretaceous placental mammals?
The most recent combination of molecular and fossil data I've seen pushes early
modern bird divergence back to almost 90 million years (the origin of
Neornithes). See Kerryn E. Slack et al, Mol. Biol Evol 23 (6) 1144-1155, 2006.
It is curious that living birds seem to have originated well before the K/T, in
contrast to mammals.
At 3:58 PM +0200 6/22/07, evelyn sobielski wrote:
>Turns out there's an upcoming paper which studies
>precisely the issue discussed here (in birds):
>Simon Y. M. Ho
>Calibrating molecular estimates of substitution rates
>and divergence times in birds
>Journal of Avian Biology (OnlineEarly Articles).
>This is probably gonna be one of those papers that
>will get cited far less often than it should be, but
>that I'll ever so often point to (not necessarily on
>this list though) ;-) I'll try to get it the next days
>and I'll be highly interested to learn what (if any -
>might be very theoretical) examples he rolls out. "For
>example, the ‘traditional’ avian
>mitochondrial substitution rate of 2% per million
>years is frequently adopted without acknowledgement of
>the associated uncertainty" should be good for one or
>two cases in point (the rate does not hold true e.g.
>for most if not all Procellariiformes, there's
>something seriously wrong with mol-clocking ratites
>but nobody really knows what it is, etc).
Jeff Hecht, science & technology writer
Boston Correspondent: New Scientist magazine
525 Auburn St., Auburndale, MA 02466 USA
v. 617-965-3834; fax 617-332-4760