|The classic image of the KT extinction: plucky mammals
emerging from burrows amidst a wasteland of dead dinosaurs
A recent study, however, has shown that they actually suffered extremely heavy losses. Analysis of the mammalian fossil record was conducted in western North America on a window from 2 million years prior to, to 300,000 years after the asteroid collision with Earth which marks the KT boundary. 'The species that are most vulnerable to extinction are the rare ones, and because they are rare, their fossils are less likely to be found,' said Dr Nick Longrich from the University of Bath. The species that tend to survive are more common, so we tend to find them. The fossil record is biased in favour of the species that survived. As bad as things looked before, including more data shows the extinction was more severe than previously believed.'
|The red line marks the KT extinction. The rapid
recovery of the modern mammal groups is apparent
'It wasn't low extinction rates, but the ability to recover and adapt in the aftermath that led the mammals to take over,' said Longrich. 'You might expect to see the same few survivors all across the continent. But that's not what we found. After this extinction event, there was an explosion of diversity, and it was driven by having different evolutionary experiments going on simultaneously in different locations.. This may have helped drive the recovery. With so many different species evolving in different directions in different parts of the world, evolution was more likely to stumble across new evolutionary paths.'
North America was closer to the epicentre of the impact event than other continents and so may have suffered a slightly higher rate of extinction than say Asia. The study, however, is based on a much larger data set than previous ones and so is certainly a more faithful representation of the change in mammal diversity across the KT boundary. Future studies may well confirm similarly high magnitudes of mammal extinction around the globe along with their phenomenally rapid recovery and subsequent ecological expansion