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

Re: Placental takeover: final comment.



> [...] I'll quote the relevant section:
> "But did the advent of condylarths within the North American western
> interior lead to the decimation of the considerable known diversity of
> Lancian native marsupials through direct competition?  That scenario was
> favored by Arch[i]bald...and indeed may have been the case.  He stated:
'Of
> special interest is that the archaic ungulate invaders had dentitions very
> similar to their marsupial contemporaries and presumably ate similar
> things.

This does not apply, of course, to any herbivorous ungulates. Archibald
seems to imply arctocyonids (which would fit putting *Protungulatum* there),
which were AFAIK carnivorous and not insectivorous and would therefore not
have competed with most NA metatherians.

This scenario also has to explain why the ancestor(s?) of *Herpetotherium*,
*Copedelphys*, *Peradectes*, *Peratherium* and *Amphiperatherium* (just
listing all Tertiary NA metatherians I know; at least some of these genera
have several species) survived and diversified. And why those basal
"ungulates" died out and e. g. don't now stop *Didelphis*, the opossum.

> It seems more than coincidence that marsupials did well in NA for
> about 20 million years only to almost disappear with the arrival of the
> ungulate clade'...

Not the placental or eutherian clade, BTW.
I also don't think that's coincidence -- what if lots of metatherians died
out at the K-T and the crown-group placentals evolved and diversified very
shortly thereafter?

> (However) the true diversity either of condylarths or
> marsupials remains unknown precisely at the boundary, and therefore one
> cannot evaluate the extensiveness of competition, if any, among species
> of the two groups at that time."
>
> They later make a plea: "the most pressing need today is for new and
> better paleontological _data_, derived from as yet unknown parts of the
> fossil record..."

Of course. I'm not going to, say, publish anything on this. But I think the
decimation of NA metatherians at the K-T does not contradict the impact
theory (I think theory rather than hypothesis has become suitable), and I
think it is not total dilletantism to post this here.

> And here I want to voice my discontent with the scientific complacency of
> some on this list.  To claim one knows what happened 65 mya--i.e., that
> placentals and marsupials were strictly casualties of an extinction
> "event" and that ecological forces were irrelevant--is to claim something
> that cannot be known.

What may not be known now, but what can be known. With ever better data, of
course. So far, I'll stick to what the present data suggest to me :-)

> But when you
> say you already know what caused species distribution at this time, you
> are ineffect saying we don't need more data.

Mmm... no. Never in science are more data useless.

> I've been reading Flannery's
> "The Eternal Frontier" with its swallowing whole of the bolide
> hypothesis as an explanation for everything.  The phrase "would
> have" gives away the _just so_ nature of of this book, as in: tsunamis
> would have...blah, blah, and firestorms would have...blah, blah.  I mean,
> it was just yesterday that everyone was warning everyone else not to make
> up stories without having direct evidence.

I haven't read the book :.-( ; however, there is evidence for global
firestorms -- the boundary layer contains lots of soot. Tsunami deposits
from the K-T are also known, but I don't know if any except
http://www.dinosauria.com/jdp/impact/breccia.htm and
http://www.dinosauria.com/jdp/impact/wham.htm have been confirmed in the
meantime.