Re: "No Bolides!"

[Adam Yates <zooamy@zoo.latrobe.edu.au>]

On Sun, 7 Apr 1996, Paul Willis wrote:

> Whoooo there boy!!!! If you are going to play the
> endothermy-for-dinosaurs-because-they-are-in-high-latitide-sites-in-Australi
> a routine you should also be aware that crocodiles, turtles and
> labyrinthodonts have also come out of these sites. This greatly complicates
> the picture and indicates that there is some problem with the palaeotemp
> data for the early Cretaceous of southern Victoria. Either that or there is
> something screwy about these particular turtles, crocs and labyrinthodonts.
> 
> Cheers, Paul

One factor that seems to be rarely discussed in connection with the polar 
dinos, is the the continually changing nature of climates. One thing that 
impressed most during my undergrad years of geology was the fractal 
nature of palaeoclimate and sealevel data. Even though the a period could 
be characterised as "warm" or "cold" there are always short lived 
excursions in other directions. This can be well seen in the Miocene 
limestones of the Murray Basin (where I collected my first fossil) where 
there are thin (a few feet at most) bands that contain abundant 
marsupiate echinoids (cold water indicators). As far as I know the evidence 
for short cold snaps is also backed up by ostracod faunas and oxygen isotope 
studies. Presumably such fluctuations occured back in the polar regions 
of the Cretaceous as well. If so the palaeotemp.data and faunal 
composition need not be at odds. I do know that the vertebrate remains in 
the victorian Cretaceous are restricted to a few clay pebble conglomerate 
lenses sporadically distributed throughout the Otway and Strezlecki 
groups. Many such lenses are completely barren, perhaps these derive from 
cold spells when no turtles, crocs, labrinthodonts OR dinos could survive 
there.  

Adam Yates
"Barny's started the LJ's again"