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Re: Dino/Birds? was Mesozoic snow?
----- Original Message -----
From: "Dora Smith" <email@example.com>
Sent: Thursday, June 16, 2005 1:27 PM
The discussion came from a discussion of Jurassic climate. Question was
whether dinosaurs ever saw snow. I asked, if they didn't, what would
have needed to develop feathers for.
"Cold" means "so cold that the costs of growing and maintaining an
insulatory cover pay off". And this doesn't mean "0 or fewer °C".
Since birds are about teh only
therapod dinosaurs that ever evolved the ability to fly, dinosaurs clearly
developed feathers for another reason, and insulating body covering is
consistent with being warm blooded. Being warm blooded has a number of
advantages, such as intelligence, speed of locomotion, and speed of
Fast growth does seem to require endothermy, but it doesn't automatically
follow as far as I know. Endothermy allows higher endurance, but I'm not
sure about pure speed. Intelligence is severely underresearched, probably so
much that next to nothing can be said. Crocodiles learn from the behavior of
their victims... it could well be that a large brain requires endothermy,
but neither absolute nor relative nor _relative relative_* brain size seem
to correlate with intelligence... at all. :-|
* Relative brain size increases with body size!
pointed out that body covering is also an advantage if it is hot or if
are temperature extremes over the course of a day - but the cold blooded
species all have ways to cope with both situations.
That's an unfair comparison. You should compare how warm-blooded animals
with and without body covering fare in the same environments. (Very
difficult, especially if one includes the insulatory effect of large body
But I had said that the triassic
was a time when Earth's climate got cool and dry.
Cool compared to when? There was a limited glaciation in the Late
Permian. -- BTW, on the global average humidity rises with temperature.
That's because evaporation rises. For a drastic example of what this means
for terrestrial life, compare the first map at
http://members.cox.net/quaternary/ with the last three.
The first ice age did not occur during the Cenezoic.
There was no ice age during the Mesozoic, that's all what's important here.
I also learned that there was a second major extinction at the end of the
Triassic, due to a large meteorite landing in Quebec, which created the
The age of that crater is very poorly resolved. However, there are _several_
craters that could fit the Triassic-Jurassic boundary. For example, there's
a twin crater in France (one of them called Rochechouart, I forgot the
other), and a single one in Ukraine (aw... how to transcribe it... let's try
Obolon'), and one in the USA (Red... Red... something... I'll have to find
the paper again... Nature 1997, I think).
This is consistent with the fact that there were ever
more than two layers of iridium.
At the same time, there was major volcanism as the continents rifted.
That's not an event. That's a process that takes tens of millions of years.
There are flood basalts associated with the Tr-J boundary, the Central
Atlantic Magmatic Province (CAMP). Their exact age is unclear, or at least
it was last time I looked...
Also, it says that "climates became more seere, with marked seasonal
and aridity in many areas." as the continents changed their location.
That was the buildup of Pangea during the Middle/Late Permian.