Re: Extinction due to "blue balls"

[Christopher Taylor <ck.taylor@auckland.ac.nz>]

Like all too many K-T extinction theories - that may work for dinosaurs, but
what about the forams?

On 21/4/04 2:08 pm, "Garrison Hilliard" <garrison@efn.org> wrote:

> Lack of females may have done in dinosaurs
> Tue Apr 20, 5:00 PM ET
> 
> 
> WASHINGTON (Reuters) - An asteroid may have wiped out the dinosaurs 65 million
> years ago not simply by changing the world's climate and causing years of dark
> skies, but also by causing too many of them to be born male.
> 
>  
> 
> If dinosaurs were like modern-day reptiles such as crocodiles, they change sex
> based on temperature, David Miller of the University of Leeds noted. And even
> a
> small skewing of populations toward males would have led to eventual
> extinction.
> 
> 
> Most experts agree that one or more asteroid impacts probably triggered a
> series
> of global changes that killed off the dinosaurs and many other species of life
> on Earth. The impacts would have kicked up dust that cooled the air and also
> triggered volcanic activity that would have created even more dust and ash.
> 
> 
> No one really knows if dinosaurs were more like reptiles, or something closer
> to
> mammals. Reptiles have very different metabolisms than mammals and also have
> various ways of determining the sex of offspring.
> 
> 
> In mammals, if a baby gets an X and a Y chromosome, it will be male and if it
> gets two X chromosomes it will be female, with a few very rare exceptions.
> Similar mechanisms work for birds, snakes and some reptiles such as lizards.
> 
> 
> But in crocodilians, turtles and some fish, the temperature at which eggs are
> incubated can affect the sex of the developing babies.
> 
> 
> Miller's team ran an analysis that showed a temperature shift could
> theoretically have led to a preponderance of males. Other studies have shown
> that when there are too few females, eventually the population dies out.
> 
> 
> "The earth did not become so toxic that life died out 65 million years ago;
> the
> temperature just changed, and these great beasts had not evolved a genetic
> mechanism (like our Y chromosome) to cope with that," said Dr. Sherman Silber,
> an infertility expert in St. Louis who worked on the study.
> 
> 
> But crocodiles and turtles had already evolved at the time of the great
> extinction 65 million years ago. How did they survive?
> 
> 
> "These animals live at the intersection of aquatic and terrestrial
> environments,
> in estuarine waters and river beds, which might have afforded some protection
> against the more extreme effects of environmental change, hence giving them
> more
> time to adapt," the researchers wrote.
> 
> 
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