Re: Dinosaurs survived in Antarctica? (Was: Re: "Dinosaurs Died W ithin Hours After Asteroid Hit Earth...")

[Michael Kaib <michael@kaib.org>]

David Marjanovic wrote:

> > IIRC mammals reached Antarctica from South
> > America around K-T time, and went on to Australia.
> >    
>
> Marsupials reached South America from North America around K-Pg time,
> and
> are present in the early Palaeocene of Australia. So, yes, I'd expect
> nonavian dinosaurs all over Outer Gondwana had any survived in
> Antarctica.
>
>  
This is new for me. My information, e.g. from the Paleogeographic Atlas 
Project at Chicago University ( http://pgap.uchicago.edu ) indicates a 
clear separation of Antarctica from Australia and from South America in 
Maastrichtian and already in Campanian. Even if the distance to South 
America was quite small and probably passable in times of low sea level 
(which were rare in Cretaceous), the distance to Australia seems to be 
absolutely infeasible for terrestrial animals. Shouldn't we better 
re-date these migrations via Antarctica to early Cretaceous?

Tim is right for Asia and NA. They have been connected in late 
Cretaceous. So there have been (only) 6 ocean-separeted continents at 
this time. That is still a lot compared to our times, with only 3.5 
ocean-separated continents: one semi-supercontinent spanning "Old World" 
and "New World", with temporary separations in Beringia, and two 
primitive continents Australia and Antarctica. The Cretaceous is the 
period of final split-up of the old supercontinent in into totally 
isolated small continent primitives. For me it sounds very likely that 
this influenced the extinction of several species, with advantage for 
those able to pass the ocean borders.

> > > -    leaving crocodiles nearly untouched
> > > at the K-T border.
> > >      
>
> Not at all. Especially if you include the terrestrial crocs -- the
> Baurusuchidae of Outer Gondwana bought the farm, too.
>  
>
> > > What happened to the other sea fauna,
> > >      
>
> Ammonites: gone. Mosasaurs: gone. 
Good point. The Mosasaur extinction is an unanswered question, too. Why 
could they become extinct at this event, while their most comparable 
rivals - crocodiles and sharks - did not suffer so much?

Thanks for the extinction rates figures. Its an importnd info that crocs 
suffered, too. Especially the terrestrials. The extinction rate of 
insects sounds surprisingly low,  assuming an average existence 
timeframe of 5 Ma for a species.