When that giant asteroid hit the planet some 66 million years ago, it wasn't just the dinosaurs that ended up pulling a short straw.
A new study by researchers at the University of Bath have since discovered that mammals very nearly went the way of the dinosaurs.
Over 90 per cent of mammals were wiped out, a far higher number than previously thought.
Dr Nick Longrich from the Milner Centre for Evolution, in the University of Bath's Department for Biology & Biochemistry, explained:
"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."
It had previously been thought that the key reason for mammals becoming so dominant after the event was simply because more of them survived.
This recent study however suggests that actually it was more down to adaptability that led them to become the dominant species.
Following the extinction event the largest animal on the planet would have been no bigger than a cat.
Many of the creatures would have survived by feeding off the dead animals that died out after the asteroid hit.
Just 300,000 years after the event it appears as though mammals had not only recovered their previous strength of diversity but had in fact doubled it.
Dr Longrich added: "Because mammals did so well after the extinction, we have tended to assume that it didn't hit them as hard. However our analysis shows that the mammals were hit harder than most groups of animals, such as lizards, turtles, crocodilians, but they proved to be far more adaptable in the aftermath.
"It wasn't low extinction rates, but the ability to recover and adapt in the aftermath that led the mammals to take over."