New version of dinosaur extinction; asteroid is not to blame

A new study by fertility experts on how higher temperatures could have led to too many male and not enough female baby dinos points to another way the dinos could have been wiped out — without an asteroid impact.

Most experts agree asteroid's impacts triggered a series of global changes that killed off the dinosaurs. The new research found the impacts would also have kicked up dust that cooled the air and triggered volcanic activity that would have created even more dust and ash.

Experts say even a small skewing of populations toward males would have led to eventual extinction.

If dinosaurs were more like modern-day reptiles such as crocodiles, they change sex based on temperature. And temperature at which eggs are incubated can affect the sex of the developing babies.

If it were like mammals, temperature's changing may cause them can't evolved the genetic mechanism to produce female, report

According to the warmer the eggs, the more males pop out, said Miller. And if the global climate was warming at the end of the Cretaceous era 65 million years ago, it could have led to too many males.

Palaeontologists and biologists had raised the idea before, said palaeontologist Dr Mark Norell of the American Museum of Natural History. But this was the first time experts in human fertility had done so.

"We thought we could bring some new angles to dinosaurs," Miller said.

It was also an opportunity to widen the horizons of fertility clinicians, Miller said, who didn't often get a chance to ponder the larger questions of how sex determination evolved and had no idea that different animals had evolved completely different approaches.

In mammals, birds, all snakes, most lizards, amphibians, and some fish, sex is determined genetically, though in different ways. For example, male mammals have a Y chromosome.

Using genes instead of temperature or another environmental condition was probably nature's way of protecting mammals from sudden climate changes, Miller said.

But genes also had their pitfalls, he said. The Y chromosome could be dying out in mammals. "[The Y chromosome] doesn't recombine with eggs," said Miller. "So eventually it will just disappear."

Whatever the mechanism, sex determination is critical for the survival of species, since the right ratios of males to females must exist to successfully propagate.

The matter is also of concern to researchers who are watching how global warming might affect modern species that use temperature to determine sex, inform

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