The dinosaurs’ extinction 66 million years ago is thought to have opened the way for mammals to dominate the land. But a new study claims many of them died off too.
“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,” said Steve Brusatte of the University of Edinburgh in the U.K., one of the authors of a report on the findings.
Among mammals, the study argues, the brunt of the disaster seems to have hit a group known as metatherians—extinct relatives of living marsupials (“mammals with pouches,” such as opossums and kangaroos.) These thrived in the shadow of the dinosaurs during the Cretaceous period, just before the extinction.
The study, published in the research journal Zookeys, finds these once-abundant mammals nearly followed the dinosaurs into oblivion.
When a 10-km (6-mile)-wide asteroid struck what is now Mexico, unleashing a global cataclysm, some two-thirds of all metatherians living in North America perished, according to the researchers. These casualties, they said, included more than 90 percent of species living in the northern Great Plains, the best area in the world for preserving latest Cretaceous mammal fossils.
Metatherians, the scientists added, would never recover their previous diversity, which is why marsupials are rare today and largely restricted to areas 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 almost everywhere today and include everything from mice to men.
“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,” said Thomas Williamson of the New Mexico Museum of Natural History and Science, lead author of the paper.
The study reviews the Cretaceous evolutionary history of metatherians and provides a family tree for these mammals based on the latest fossil records, which researchers said allowed them to study extinction patterns in unprecedented detail.
Source : www.world-science.net