How Humans' Ancestors Survived Asteroid Impact That Killed Dinosaurs

Dinosaurs went extinct about 66 million years ago and the most popular theory about their mass exit is that the destruction triggered by a hail of asteroids hitting the Earth wiped them all out. However, a study has shown that the mammals, including human's ancestors, managed to survive that catastrophic destruction.

According to an in-depth research of the fossil record, a Cretaceous origin for placental mammals, which include humans, dogs and bats, indicating they co-existed with dinosaurs for a short period before the dinosaurs disappeared, a phenomenon termed as Cretaceous-Paleogene (K-Pg) mass extinction. Molecular data has long suggested an older age for placental mammals.

Debate has long raged among researchers over whether placental mammals were present alongside the dinosaurs before the mass extinction, or whether they only evolved after the dinosaurs were done away with. Fossils of placental mammals are only found in rocks younger than 66 million years old, which is when the asteroid hit Earth, suggesting that the group evolved after the mass extinction.

In a new paper published in the journal 'Current Biology', a team of palaeobiologists from the University of Bristol and the University of Fribourg, used statistical analysis of the fossil record to determine that placental mammals originated before the mass extinction, meaning they co-existed with dinosaurs for a short time.

However, it was only after the asteroid impact that modern lineages of placental mammals began to evolve, suggesting that they were better able to diversify once the dinosaurs were gone. The researchers collected extensive fossil data from placental mammal groups extending all the way back to the mass extinction 66 million years ago.

Lead author Emily Carlisle of Bristol's School of Earth Sciences said: "We pulled together thousands of fossils of placental mammals and were able to see the patterns of origination and extinction of the different groups. Based on this, we could estimate when placental mammals evolved."

Co-author Daniele Silvestro of University of Fribourg explained: "The model we used estimates origination ages based on when lineages first appear in the fossil record and the pattern of species diversity through time for the lineage. It can also estimate extinction ages based on last appearances when the group is extinct."

The other co-author Professor Phil Donoghue, also from Bristol, added: "By examining both origins and extinctions, we can more clearly see the impact of events such as the K-Pg mass extinction or the paleocene-eocene thermal maximum (PETM)."

Primates, the group that includes the human lineage, as well as Lagomorpha (rabbits and hares) and Carnivora (dogs and cats) were shown to have evolved just before the K-Pg mass extinction, which means their ancestors were mingling with dinosaurs. After they survived the asteroid impact, placental mammals rapidly diversified, perhaps spurred on by the loss of competition from the dinosaurs.

(With inputs from agencies)