Re: Mesozoic snow?

[Amtoine Grant <ajgrant@eastlink.ca>]

On Sunday, June 12, 2005, at 02:10  PM, Dora Smith wrote:

> I have a question;  just how DO we know that the climate was cooler 
> during the Triassic?

When did anybody say this? To my understanding and last I recall 
reading in The Scientific American Book of Dinosaurs, the Trisassic 
climate was a "persistently, seasonally hot, periodically monsoonal, 
arid environment" with widespread desert & sand dune deposits. This is 
apparently backed up by pretty much worldwide presence of "red beds", 
rocks predominantly stained red from iron oxide, a chemical signature 
associtated with such a climate.

> If we know it was cooler, we should be able to know how cool it was, 
> and this would tell us if dinosaurs ever saw snow.
>
> Well, that and the precipitation level.  We also somehow know that it 
> was dry.   Nevertheless, plants and certain large warm blooded and 
> often feathered reptiles managed to thrive.

What feathered reptiles were these? Are you referring to Longisquama? 
AFAIK, there are supposed feather impressions were a dilophosaur sat, 
although some[maybe most] people claim that these are drag marks. The 
earliest undisputedly feathered dinosaur is Archaeopteryx, if I recall 
correctly, from the Late Jurassic.

> Common sense does lead one to wonder how feathers were an advantage if 
> the temperatures continued to be tropical.

Didn't the worldwide climate cool considerably in the Jurassic period, 
with a climate or climates more closely resembling the present? if this 
is actually true, if feathers had not yet evolved, it could be that the 
cooling was the driving reason for their development in the smaller 
theropods. The larger branches that could get get by by virtue of their 
size's heat-retainment would not have needed to. OR, growing larger 
could have been their alternative solution to the problem(as opposed to 
developing feathers for insulation).