The extinction of the dinosaurs 66 million years ago is thought to have paved the way for mammals to dominate, but a new study shows that many mammals died off alongside the dinosaurs.
Dr. Steve Brusatte of the University of Edinburgh’s School of GeoSciences was one of a team of paleontologists who discovered that some of the most common mammals living alongside dinosaurs were also nearly wiped out when an asteroid hit the planet 66 million years ago.
Dr. Steve Brusatte said:”The classic tale is that dinosaurs died out and mammals, which had been waiting in the wings for over 100 million years, then finally had their chance.
“But our study shows that many mammals came perilously close to extinction. If a few lucky species didn’t make it through, then mammals may have gone the way of the dinosaurs and we wouldn’t be here.”
The study, by an international team of experts on mammal evolution and mass extinctions, looked at metatherian mammals-the extinct relatives of living marsupials (“mammals with pouches”, such as opossums) and found that while they thrived in the shadow of the dinosaurs during the Cretaceous period, they 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, around two-thirds of all metatherians living in North America perished.
This included more than 90% of species living in the northern Great Plains of the USA which is the best area in the world for preserving Cretaceous mammal fossils.
In the aftermath of the mass extinction, metatherians never recovered their previous diversity, which according to scientists, is why marsupial mammals are rare today and largely restricted to unusual environments in Australia and South America.
The study found that placental mammals- which include everything from mice to men.- took advantage of the metatherian demise.
Dr. Thomas Williamson of the New Mexico Museum of Natural History and Science, lead author on the study, said: “This is a new twist on a classic story.
“It wasn’t 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.”
The new study is published in the open access journal ZooKeys. It reviews the Cretaceous evolutionary history of metatherians and provides the most up-to-date family tree for these mammals based on the latest fossil records, which allowed researchers to study extinction patterns in unprecedented detail.
The work was supported by the US National Science Foundation and the European Commission. Dr. Gregory Wilson of the University of Washington also took part in the study.