Could the enduring mystery of why the dinosaurs died out come down to how sex was determined in the group of animals.
Credit: Peter Shouten
SYDNEY: Why the dinosaurs died out 65 million years ago may come down to how the sex of their offspring was determined, said American palaeontologists and microbiologists.
To determine the sex of offspring, not all animals use genetics the way humans do (with an XX chromosome pair resulting in a female and XY a male offspring).
Instead, many groups of animals use the temperature of eggs during incubation. For example, Australian salt water crocodiles hatch as females if the average temperature of the mound nest is below 29°C or above 34°C, but male if the average temperature is in between.
Accidental all-male populations?
Until now, it was thought that 65 million years ago non-avian dinosaurs and other species with temperature-dependent sex determination went extinct following a volcanic eruption or enormous meteorite impact because such an event resulted in a global climate change that completely skewed the sex ratios of offspring.
But this hypothesis was discounted in a study published this week in Biology Letters.
A team of palaeontologists and microbiologists looked at the fossil record of 62 species in the Hell Creek and Tullock Formation in Montana to see if they survived the transition from the Cretaceous to Palaeogene 65 million years ago. The species were from groups such as salamanders, frogs, toads, turtles, lizards, marsupials, birds, crocodiles and alligators.
Species that survived 65 mya
"We were able to determine the SDMs [sex-determining mechanisms] of 62 species; 46 had genotypic sex determination (GSD) and 16 had TSD [temperature-dependant sex determination]," the researchers, from the U.S. and Mongolia, wrote in their paper.
"Most surprisingly, of the 16 species with TSD [temperature-dependent sex determination], 14 of them survived into the Early Palaeocene. In contrast, 61% of species with GSD went extinct."
"Our results were definitely unexpected," said Jonathan Geisler, anatomist and palaeontologist at the New York College of Osteopathic Medicine, USA.
"We do not have a compelling explanation" for why groups of animals that used temperature instead of genetics fared better 65 million years ago, the researchers wrote.
