Early mammals thrived long before demise of dinosaurs

New York:Mammals began flourishing long before the mass extinction that ended the age of the dinosaurs 66 million years ago, says new research, which is contrary to the prevailing notion that the mammal evolution was curbed by the success of the land-based reptiles.

Therian mammals — those that give birth to live young without using a shelled egg — actually began their massive diversification ten to twenty million years before the extinction that ended the age of the dinosaurs, the researchers said.

The findings showed that the mammals that lived during the years leading up to the dinosaurs’ demise had widely varied tooth shapes, meaning that they had widely varied diets.

“This study shows that therian mammals, the ancestors of most modern mammals, were already diversifying before the dinosaurs died out,” said lead author David Grossnickle, doctoral candidate at the University of Chicago.

Also mammals had developed a wide range of diets and ecological roles about 10 to 20 million years before the dinosaurs were wiped out.

For the study, the team analysed the molars of hundreds of early mammal specimens from the Field Museum of Natural History in Chicago.

“The early therians were probably insect-eating small creatures like small rodents or shrews, but right before the [mass extinction] there is definitely evidence that there are some plant-eating therian mammals and some more carnivorous therian mammals,” Grossnickle added in the journal Proceedings of the Royal Society B.

This increase in diversity could be linked to large evolutionary changes among flowering plants that took place during a similar period.

Flowering plants might have offered new seeds and fruits for the mammals. And if the plants co-evolved with new insects to pollinate them, the insects could have also been a food source for early mammals, the researchers pointed out.

Further, the results showed that early mammals were hit by a selective extinction at the same time the dinosaurs died out — generalists that could live off of a wide variety of foods seemed more apt to survive, but many mammals with specialised diets went extinct.

“The types of survivors that made it across the mass extinction 66 million years ago, mostly generalists, might be indicative of what will survive in the next hundred years, the next thousand,” Grossnickle noted.