Re: more dinosaur extinction stuff

[John Alroy <jack@homebrew.uchicago.edu>]

Regarding the pineal gland theory:

1) If you look long enough for a consistent anatomical difference  
between any arbitrary Group A and Group B, you WILL find one. It just  
stands to reason that you will because there are countless dozens,  
hundreds, or even thousands of possible differences. This is just  
like going through the roster of a losing World Series team until you  
find an ex-Cub, and then declaring that the team lost BECAUSE of the  
Cubs' curse (yeah, I know, it's supposed to be three Cubs).  
Therefore, one should be really cautious about the "fact" that  
dinosaurs all had anatomical feature X or Y "proving" that that was  
the cause of their extinction.

2) The K-T extinction was not just a DINOSAUR extinction, it was  
GLOBAL MASS EXTINCTION. The current best estimate is that 70 - 76% of  
ALL marine animals went extinction at the K-T. This is nothing to  
sneeze at, and I'm sure it has nothing to do with pineal glands.  
Furthermore (and more to the point), "mammals, lizards, fish, birds  
etc" DID suffer an extinction at the K-T. For example, the mammals  
lost about 1/3 of their genera and 1/2 of their species. My friend  
down the hall has data showing a similar global extinction for  
crocodylians. Birds have virtually no record in this interval, and we  
can argue about teleosts, amphibians, squamates, and turtles some  
other time. Dinosaurs weren't the only large vertebrates going  
extinct at the K-T: so did the icthyosaurs and the plesiosaurs (not  
to mention the pterosaurs).

3) As I've argued before, it's just ecological common sense/general  
knowledge that when the going gets rough, large body size is a  
serious handicap. Large animals have small populations, slow rates of  
intrinsic population increase, and generally high rankings on the  
trophic "scale"; those are very serious drawbacks in the face of a  
catastrophe. In other words, the meek DID inherit the Earth, and  
that's just what any community/population/conservation ecologist  
would predict.

In summary, I think we should hold off on speculating about dinosaur  
extinctions until someone can disprove the body size hypothesis  
combined with the standing null hypothesis - that dinosaurs,  
plesiosaurs, ichthyosaurs, pterosaurs were just a few petty little  
groups (which is exactly what they were from the perspective of  
global diversity) that got unlucky at the K-T, losing all of their  
diversity instead of "just" half or more like the mammals.