Why dinosaurs died: it's all about sex

ST. LOUIS, April 20 (UPI) -- A St. Louis physician has found evidence the reason weather changes may have killed off dinosaurs has to do with sex selection.

According to an article in the journal Fertility and Sterility released Tuesday, Sherman Silber's theory depends on a large meteor impact raising sun-blocking dust clouds that cooled the planet and weakened the food chain by stunting vegetation's growth.

His article says such chilly temperatures would also have affected the incubation of dinosaur eggs.

If the dinosaurs' mechanism of sex determination was temperature-dependant, like the modern crocodilians, and if cooler temperatures resulted in a dearth of females and a preponderance of males, the dinosaur population would have slid into an irreversible decline in just a few generations' time.

"Without a sex-determining chromosome, the sex of the offspring is determined purely by the temperature in which the eggs are incubated," Silber said.

"Since an evolution of a sex-determining chromosome is the ultimate cause of the deterioration of sperm production, we pondered why nature would keep on producing such a system. Then the answer became clear from our mathematical and paleontological review."