Posted on 04/21/2004 11:45:26 AM PDT by Junior
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, U.S. and British researchers say.
If dinosaurs were like modern-day reptiles such as crocodiles, they change sex based on temperature, David Miller of the University of Leeds in Britain and colleagues noted Tuesday. 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.
So do Jeter and ARod, but boy do people get their panties in a bunch when anyone points it out . . .
What an interesting idea. Scientists are always writing "stupid" papers (which can never be proved) and getting paid for their "brilliance".
ROTF!!! Paleoretro-sexual?
Believe it or not, the initial successors in the megafaunal niches were birds. Of course, that didn't last long...
Why did the Ichtysaurs (sp?) die out, then? Wouldn't they have also benefited from living in the oceans?
A problem with that hypothesis is that there were plenty of "microfauna" dinosaurs too (non-bird variety), and they died out as well.
They weren't insulated with feathers the way birds were.
Mike
Hence the eggs would have survived a global cooling caused by the dust thrown up in the asteroid hit.
And consequently, the reason of crocodilians surviving because of living in the intersection of land and water is moot. Why? Because if that was the case then aquatic species of dinosaur would have also survived the cooling! (Although the LochNess/lake Champ 'witnesses' would claim Nessie and Champ are aquatic dinosaurs ....but i won't go there).
In my opinion, in the event of an asteroid hit churning up dust, the only thing that would have saved crocodilians and turtles is their habit of thermo-regulating their eggs by burrying them in earth. And certainly not to them living where earth and water meet, because if that theory was true swimming in lakes and oceans today may lead to a mano-a-mano meet with 40 feet of swimming scales and teeth with a name ending with 'saurus.'
Spetz's theory: laying the eggs in holes covered with earth and decaying compost saced the crocodilians. Water and earth meeting had little or no effect whatsoever, and if the crocodiles laid their eggs and left them in the sun (as the dinosaurs probably did) the cooler temperatures would have done them in too. Remember the eruption of some mountain in the 1800s that caused winter to last for a whole year (the funny thing is that scientists then were blaming it on 'experiments with electricity' and on lightning rods 'stealing heat from the sky' when the real cause was a violent eruption sending ash that effectively cooled the whole earth).
Now, to get a timemachine so as to see if that is as it happened!
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