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Re: K/T impact (was Re: [for some reason] Tim's theory)



> John Bois wrote:
>
> >Since there is _no record_ of the extinction of enantiornithines, this
> >statement cannot be made.
>
> Enantiornithines are found in the Late Cretaceous, but not in the
Paleocene.
>   That's good enough for me.
>
> >Marsupial extinctions are also consistent with placental replacement
> >hypothesis.  How to choose between the two?
>
> How indeed.

By looking at the distributions of meta- and eutherians at that time. If
eutherians (include placentals) are thought to originate from Asia (this is
not completely sure, AFAIK) and were superior competitors to metatherians
(include marsupials), then we'd expect that there were no marsupials in LK
Asia. This is not so. Several are known (including *Deltatheridium*) (ref
tomorrow). We'd also expect that metatherians died out everywhere where
placentals got in the Cenozoic. As I have mentioned before, in NA and Europe
metatherians died out no sooner than the Miocene (the youngest ones here in
Austria are 17 Ma old). Hey, they got into Europe, which was impossible
before the K-T, and even shortly invaded Africa!!! Opossums etc. survived
the Great American Interchange that began 3 Ma ago or so and have now
expanded their range into Canada.
Placentals and marsupials reached SA together somewhere around the K-T. Even
the dryolestoids and gondwanatheres -- endemic mammals -- didn't die out
before the Paleocene.
In short, marsupial extinctions at the K-T in NA aren't consistent at all
with placental replacement. Makes the choice rather easy.