Human ancestors 'survived asteroid that killed dinosaurs'

Illustration of the K T Event at the end of the Cretaceous Period. A ten-kilometre-wide asteroid or comet is entering the Earths atmosphere as dinosaurs, including T. rex, look on.
Human ancestors walked the Earth at the time of the extinction of the dinosaurs. (Getty)

Human ancestors walked the earth at the same time as the dinosaurs, a new study has shown.

Placental mammals, a group which includes humans, dogs and bats today, co-existed with dinosaurs for a short time before the dinosaurs went extinct.

Researchers analysed fossils and concluded that up to 21.3% of placental mammal families might stretch back to the Cretaceous.

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 mass extinction.

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After they survived the asteroid impact, placental mammals rapidly diversified, perhaps spurred on by the loss of competition from the dinosaurs.

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.”

The researchers used mathematical analysis to estimate when different mammal families might have gone extinct.

Co-author Daniele Silvestro, from the 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.”

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The research may help to understand other mass extinctions, the researchers believe.

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).”

The catastrophic destruction triggered by the asteroid hitting the Earth resulted in the death of all non-avian dinosaurs in an event termed the Cretaceous-Paleogene (K-Pg) mass extinction.

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. However, molecular data has long suggested an older age for placental mammals.

The researchers 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.

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