[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: paleontolgist, dinosaur



On Fri, 8 Nov 1996, Stan Friesen wrote:

> The volcanic eruptions probably effected global climate, and perhaps
> induced extensive acid rain wrold-wide.

Which would not have targeted dinosaurs specifically I don't think

> The lowering of sea levels changed climates from maritime to continental
> over lare areas, reduced the extent of continental shelf (contributing
> to the *marine* extinctions), and perhaps reduced the habitat variety
> on land as well.

Loss of habitat variety affects _all_ creatures.

> The effects of the impact have been well covered elsewhere.

Yes, but how it impacted dinos is speculative only.

> The interesting thing is that ??Archibald's data (in the recent book on
> the extinctions) is, according to him, more in line with causation by
> the Deccan volcanism than by an impact. (If I remember correctly he
> concludes that no one single cause quite matches observed pattern of
> extinctions - which also supports my multi-causal model).

In _Dinosaur Extinction and the end of an era: what the fossils say_, 
Archibald gives marine regression the most blame for killing dinos off.  
On pp 204 he says:  "As marine regression quickened, the coastal habitats 
decreased ever more rapidly.  The larger vertebrates--dinosaurs--were the 
first to experience declines...The coastal plains dinosaurs certainly 
were capable of migrating from one shrinking coastal habitat to another, 
but finally even this could not arrest further decline...Smaller 
terrestrial vertebrates were also declining, but because of shorter life 
spans and quicker turnover rates, they adapted more quickly to the 
environmental changes."

        At first glance this seems reasonable.  But let me say the 
same thing another way: Neither in what is now Africa, nor Australia, nor 
Antarctica, nor Europe, nor Asia, nor on any Komodo-like island 
sanctuary, in none of these places was there habitat enough to support 
one dino species.  I just find that very hard to believe.

        Even his seemingly obvious point about quicker turnover rates can 
be questioned.  Listen to Greg Paul's conclusion about the ability of 
dinos to adapt from  _Dinosaur reproduction in the fast lane_ in Dinosaur 
Eggs and Babies (ed. K. Carpenter): "The history of the dinosaurs is 
marked by remarkable success and stability during the Mesozoic.  Far from 
being inherently vulnerable, the dinosaurs survived in spite of repeated 
changes in sea level and climate...Indeed, the dinosaur's fecundity makes 
it hard to see how such resilient animals could ever have been killed 
off."  And: "(dinosaur fecundity) was an important factor in their 
ability to exploit new conditions and made their capacity exceptionally 
high to resist and recover rapidly from severe environmental 
disruptions--so much so that no hypothesis of dinosaur extinction fully 
explains their demise."

        Amen.

> I suspect that the changes in mineral and oxygen cycling might also
> effect climate and land ecology (by changing the limiting resources
> for plant growth, for instance).

        But having a long list of suspects doesn't mean you've solved the crime.
  
> Here is another bit of evidence:
> Amoung all of the various mass extinctions, and near-mass extinctions,
> the most commonly co-occuring events are oceanic anoxia and flood basalt
> volcanism such as produced the Deccan traps. (For instance, the Permo-
> Triassic extinctions are associated with oceanic anoxia, two different
> flood basalt zones, and extreme low sea levels, not to mention the
> continental glaciation).

        How many angels can dance on the end of a needle?