[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

RE: K-T mammals



 
Something worth considering (and maybe it's been studied already, at least
to some degree)...

There is evidence that in North America (anywhere else?) the K/T boundary
was immediately preceded by a decline in dinosaur diversity.  However, there
is also abundant evidence that the K/T boundary was marked by extinctions
across a wide range of groups - on both the micro and macro scales.  As
someone mentioned, the bolide impact might have delivered a coup de grace to
the already-declining North American dinofauna.  But there's no reason to
believe (and we'll never know) that this decline was terminal.

Even if there was a drop in the number of dino taxa a few million years
prior to the end of the Cretaceous, I'd be surprised if this was the first
and only gradual decline in the 160-million year history of dinosaurs.  A
lot of attention is paid to the end-K, for obvious reasons.  Dino diversity
(i.e. number of species) may have spiked and troughed many times over 160
million years (aside from the Triassic-Jurassic and Jurassic-Cretaceous
boundaries).  I favor the hypothesis (and that's all that it is) that the
dip in dino diversity seen in North America coincided with an
extraterrestrial impact that finished 'em off.

On the flipside, we actually have no evidence that in some places (e.g.
Australia, Antarctica) the non-avian dinosaurs did go extinct at the K/T
boundary.  (On the other hand, there's no evidence that they didn't.)

By the way, I received a worm/virus (my software nixed it either way)
entitled "End global footer, PrfCopyright.hti".  Beware, if you don't have
protection.



Tim