Thursday, 18 December 2014

Dinosaur asteroid took mammals to brink of extinction

The asteroid that wiped out dinosaurs 66 million years ago nearly took early mammals to extinction, a new report reveals. Researchers in Scotland and the US studied the evolutionary history of mammals in the Cretaceous period and found that they were almost wiped out with the dinosaurs.

[caption id="attachment_112" align="alignleft" width="590"]Ka-boom! Out with a bang. Artist rendering of asteroid impacting Earth. Image Credit: NASA/Don Davis.[/caption]

Before the 10-km-wide space rock crashed into what is now Mexico, dinosaurs ruled the Earth. Lower down the food chain were two types of mammals: the marsupial-like metatherians (ancestors to kangaroos) and the placental mammals (who birth well-developed offspring).

Metatherian mammals were the dominant of the two mammal types but, after the asteroid impact, two-thirds of all metatherians went extinct and their diversity never recovered. Today, their descendants are found in niche environments in Australia and South America.

Placental mammals filled the gaps left behind with the demise of their predators, the reptilian dinosaurs, and decimation of their main competitors for resources, the metatherians.

Study author Dr Thomas Williamson, of the New Mexico Museum of Natural History and Science, commented, “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.”

Dr Steve Brusatte, of the University of Edinburgh, highlights how substantial the Cretaceous mass extinction was, “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.”

There but for the grace of god go we. Today, scientists believe that the Earth is undergoing another mass extinction event as tens of thousands of species are threatened – in no small part due to human expansion.

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