Re: Dino/Birds? was Mesozoic snow?

[David Marjanovic <david.marjanovic@gmx.at>]

----- Original Message -----
From: "Dora Smith" <villandra@austin.rr.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 
> they
> 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 
> growth,

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!

> Someone
> pointed out that body covering is also an advantage if it is hot or if 
> there
> 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 
size...)

> 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
> Manicouagan Crater.

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 
> changes
> and aridity in many areas." as the continents changed their location.

That was the buildup of Pangea during the Middle/Late Permian.