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Re: Polar dinosaurs
> Tracy Ford wrote:
> I was looking at the book?Black Opal Fossils of Lightning Ridge? and
> started thinking about those supposedly ?furry? hypsilophodonts. The
> hypsilophodontids are used as an indacator for long dark cold nights
> and being able to survive them. But what about the other animals?
> Sharks, fish,
Anti-freeze agents in the blood perhaps? The Greenland sleeper shark
lives under the ice flows.
If they were warm blooded, perhaps a layer of blubber. Otherwise they
may have had to migrate (fresh water plesiosaurs may have moved out of
rivers into the ocean, like South American bull sharks). Or the
anti-freeze solution again.
> Crocodiles (hibernate?)
Crocs don't appear in the older deposits of S.E. Australia. They are
absent from the Strzelecki deposits (115 MYA), only appearing in the
later Otway deposits (Dinosaur Cove, 106 MYA). There is also no sign of
labyrinthodonts in these later deposits - perhaps direct competition
drove them to extinction. Maybe crocs could endure (hibenate?)
temperatures down to a certain level, and had to wait for the region to
warm up a bit before moving in.
> Large sauropods? They couldn?t hibernate and weren?t covered in ?fur?.
There are no sauropod remains in the extreme south of Australia, only in
the north of the country. Perhaps like crocs, they could tolerate a
certain level of coldness, but not as much as other animals (hypsies,
etc), which kept them only in the more northerly regions of Oz.
> Dromaeosaurids? (Insulation?)
Dromaeosaur-like teeth are in the same deposits as hypsie material down
south. Perhaps smaller carnivores stuck around during the colder months
(small creatures eat less - arctic foxes make a good living where wolves
generally struggle to survive). Large theropods could always have
migrated north when things got too cold, returning in the long summer.
Incidently, the "dromaeosaurid" teeth frm Victoria have serrations only
on the posterior edge. Do basal dromies like Saurornithosaurus also show
this, or do they have serrations on both edges?
> Birds? (Insulation? Migration?)
The only bird evidence from the extreme south of Oz are bird feathers in
the Koonwarra deposits (formed when the shallows of a lake froze over
during the winter). The feathers are in good condition and don't look
like they had been lying around for weeks or months before ending up in
the lake. Perhaps this is evidence that some birds stuck it out during
the winter months? It would be great if we were to find bird or small
theropod fossils in these deposits. There's a real possibility of
integumentary structures being preserved.
> So how did the larger animals survive the cold?
It's hard to say in the Victorian deposits. They seem to have been
formed by river deposits coming to rest. Larger material seems to have
been left behind somewhere up stream, with a bias towards the smaller,
more easily transported material. Therefore it may be hard to say with
certainty whether larger animals vacated the region during the colder
winters or not. Perhaps the "Walking with Dinosaurs" scenario was partly
right. Larger animals migrating, leaving those smaller animals, less
able to make large journeys, to endure the winter. Of course I have
trouble seeing Muttaburrasaurus getting that far south. They would have
had to cross some major stretches of open ocean to get from Victoria to
Queensland during the Early Cretaceous.