Dinosaur-killer asteroid nearly wiped out mammals too

Many mammals came perilously close to extinction when a massive asteroid hit the earth 66 million years ago, says a study, adding that if a few lucky species did not make it through then mammals may have gone the way of the dinosaurs.

The extinction of the dinosaurs 66 million years ago is thought to have paved the way for mammals to dominate but many mammals died off alongside the dinosaurs.

Metatherian mammals - the extinct relatives of living marsupials ("mammals with pouches") thrived in the shadow of the dinosaurs during the Cretaceous period.

Now, an international team of experts on mammal evolution and mass extinctions shows that these once-abundant mammals nearly followed the dinosaurs into oblivion.

When a 10-km wide asteroid struck what is now Mexico at the end of the Cretaceous and unleashed a global cataclysm of environmental destruction, some two-thirds of all metatherians living in North America perished.

This includes more than 90 percent of species living in the northern Great Plains of the US, the best area in the world for preserving latest Cretaceous mammal fossils.

In the aftermath of the mass extinction, metatherians would never recover their previous diversity, which is why marsupial mammals are rare today and largely restricted to unusual environments in Australia and South America.

Taking advantage of the metatherian demise were the placental mammals: species that give live birth to well-developed young. They are ubiquitous across the globe today and include everything from mice to men.

"This is a new twist on a classic story. It was not only that dinosaurs died out, providing an opportunity for mammals to reign, but that many types of mammals such as most metatherians died out too - this allowed advanced placental mammals to rise to dominance," explained lead author Thomas Williamson from the New Mexico Museum of Natural History and Science.

The findings were detailed in the open access journal ZooKeys.