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Re: (extinction) (long)



On Monday, I wrote

> How old is the base of the Ferris Fm, and how was it dated? I can remember
> the times when they used the lowermost coal bed to find it

The K-T boundary.

> in the Hell Creek Fm, but it

The coal bed (Z-coal).

> is diachronous.

-------------------------

It's possible to obtain molecular dates that agree pretty well with the
fossil record (almost all divergences happening in the Paleocene), at least
for mammals. Just depends on what calibration point is used.
www.jsbi.org/journal/GIW01/GIW01F15.pdf is a very interesting paper on that.
4 different sets of molecular dates, obtained from the same cladogram, are
provided in Table 2. That the whale-hippo split (oldest whales 52 Ma)
produces extremely old dates (Placentalia as old as the Cretaceous, rest of
dates strewn across the K) might even be evidence against Whippomorpha
(which is _consistently_ found in all molecular phylogenies, though). The
authors are so friendly as to provide an answer to why the horse-rhino split
(55 Ma) also produces pretty high divergence times, while the tarsier-human
split, also 55 Ma, produces the lowest ones -- horses and rhinos began small
and therefore evolved fast at first, then they grew and their evolution
slowed down. Molecular clock rates vary with generation time.

Said paper introduces a few new names. Those that replace old ones are
Boreotheria (for Boreoeutheria, but maybe it's just somebody's reading
error) and Supraprimates (for the yucky Euarchontoglires).