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Re: feathered ornithopods?
"Tracy L. Ford" wrote:
> We do not know this for sure. This is an assumation due to modern times and
> we can in no way know whether or not it actually did get frosty. We happen
> to be at different ends of this.
Lets look at the evidence:
- Cryoturbational geological structures, associated with both permafrost
and "hummocking". Mean annual temperature (MAT) estimated at between -6°
and 3° celsius based on these.
- Iceberg/glacial dropstones in the ocean that covered much of the state
of South Australia.
- O-18 isotope studies suggesting an MAT of -2° +/- 5° celsius.
- The Koonwarra insect community suggesting a similar make up to that of
modern alpine insect communities.
> So can crocodilians (in Florida and Lousiania). But labyrinthodons had
> scales (which may or may not work for or against a cold climate) not like
> modern amphibians.
There are labyrinthodont remains dating to 120 MYA, but no crocs. Things
warm up a tad by about 115 MYA - you find croc remains, but no more
labyrinthodonts. This suggests that crocs outcompeted the labys, the
prevailing theory for the rest of the world as well, and that labys
survived in this area to the Early Cretaceous because crocs were kept
out, probably by cold temperatures.
> Right and I just wanted to qualify my point. There are animals that weren't
> marine and that is the point I'm tyring to make.
It is indeed a "tyring" point... :)
Plesiosaurs in Australia and other parts of the world (ie. Antarctica,
New Zealand) seem to have prefered breeding in colder climates (perhaps
due to lack of predators?). There are more juvenile marine reptile
remains known from South Australia than those of adults (a ratio of
about 19:1). This is the same South Australia with the dropstones.
Hypsilophodontids may have also chosen the polar areas to breed in.
There are lots of juvenile remains found in Victoria and South
Australia. One specimen, probably a Leaellynasaura, was found with an
advanced osteomyelitic infection of the tibia. The other tibia grew
another 27 mm, indicating the animal lived for quite a while with the
condition. None of the bones show signs of scavenging. So, you've got an
animal that lived for a while without being able to run, and wasn't
scavenged when it finally died. This suggests to me that predators were
pretty thin on the ground, perhaps why the hypsies chose this area to
breed in (like a modern version of Arctic geese).
> Hows about Lightning Ridge? [sauropod remains]
Not as far south as southern Victoria. They may have moved to the
central parts of the continent seasonally (seas barriers permitting),
travelling north to breed (hence the sauropod "herds" moving along the
coast of Broome - migration?). Much like a land-bound whale. Tom Rich
has argued that sauropods will never be found in southern Victoria. So
far he's been right.
Dann Pigdon Australian Dinosaurs:
GIS / Archaeologist http://www.geocities.com/dannsdinosaurs
Melbourne, Australia http://www.alphalink.com.au/~dannj/