Re: Dinosaur extinction

[Bill Adlam <wa105@mead.anglia.ac.uk>]

If you're bored with the topic, you won't miss anything by deleting this 
message.

Speaking as a non-specialist...

Summary of John Clavin's post:

>>Major theories:
>>1)  Meteorite/Asteroid/Bolide impact:...
>>2)  Deccan Traps volcanic eruption:...
>>3)  Destruction of Pangea...
>>4)  Changes in patterns of flora and fauna...
>>5)  Lots of others...

Andreas Kolle wrote:

>In my opinion, these still solve little or nothing.
>1) Dinos froze to death. Why didn't the crocodiles? They are to big to hide
>and they do (as far as I know) not hibernate. They are extremely
>temperature dependent (pardon my spelling), and only get female offspring
>in cold weather. If they managed to survive at the time because they found
>a way out, why have thy lost that ability?

John never actually said that dinos froze to death.  We know that some 
could survive low temperatures because a few have been found at high 
palaeolatitudes (i.e. in places which were then fairly close to the poles) 
in North America and Australia.  Winter temperatures there at that time 
probably dropped to about freezing point.

A worldwide cold spell over the course of a few centuries, maybe just a few 
years, would be a disaster for nearly all animals.  While high-latitude 
dinosaurs may have been able to migrate towards the equator, their food 
plants couldn't.  Regardless of whether they could survive the cold, large 
animals like dinosaurs would not have enough food to survive.  If dinosaurs 
were warm-blooded, they would have needed about ten times as much food as a 
crocodilian of the same size.

Two modern crocodilians, the Chinese and Mississippi alligators, go into a 
state of hibernation or at least torpor in the winter.  All spend much of 
their time in the water and feed at least partly on aquatic animals such as 
fish.  Animals which live underwater are more likely to survive a cold 
winter because under the ice, temperatures are always above freezing.  
(Sounds obvious when I put it that way.)

Your spelling is right, BTW.

>2)Same problem, besides I sincerely doubt that vulcanoes errupting was a
>new thing in the K/T period.

Extremely large lava flows like the Deccan Traps are very unusual.  

>3)Memory might serve me wrong, but I thought that pangea only was a
>jurassic phenomenon. However, it explains that some areas got cold, but
>others must have remained warm, ad why did they die?

To put it in the simplest terms as I can (in fact the only terms I can),  
Pangea had formed by the start of the Permian.  Late in the Triassic it 
split into Gondwanaland (south) and Laurasia (north).  These two 
supercontinents sparated in the Jurassic and themselves split up in the 
Cretaceous.  These processes had hundreds of different consequences for the 
global climate.

>4) Changes always happen. I doubt that no dino could adapt.

It's clear that apart from birds, no dinosaurs did adapt to survive the 
conditions at the end of the Cretaceous.

>From the fossils, there were two aspects to the end of the dinosaurs: a 
?gradual decline and a sudden fall.  Dinosaurs became less diverse (but no 
less common) during the second half of the Cretaceous, then the surviving 
groups (except for birds) and many other organisms were suddenly wiped out.  
Theories 3 and/or 4 may explain the decline, but 1 and/or 2 are more 
promising as reasons for the fall.

>Sad about that religous part. I think many people forget that we do not
>deal with absolute facts here. Sounds like Thomas Kuhn has got a point...

Pangea is an excellent illustration of it.  It was proposed by Wegener (not 
a geologist) in 1912 on the basis of a wide range of evidence.  It was 
rejected because no-one could imagine a way to move whole continents.  
Continental drift was rapidly taken up in the 1960s after a relatively 
glamorous 'big science' survey revealed stripes of magnetism in the seabed.

                                                        All the best,

                                                                        Bill