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Mammals took control well before dinosaurs became extinct

Credit: Wikimedia Commons

According to a study, mammals began to grow and expand well before dinosaurs became extinct.  This growing diversity could be related to a link with the growth of flowering plants. 

We often think that dinosaurs dominated their environment before they became extinct. During this time it is commonly believed that the first nocturnal mammals waited “in the shadows” looking for their chance.  Some studies have suggested that our ancestors couldn’t have started to really develop until after the disappearance of terrestrial dinosaurs.  However a study published in the Actes de la Royal Society B stated a few months ago that mammals started diversifying well before:  at least 10 to 20 years before the end of the dinosaur age..

The traditional view is that mammals were suppressed by the dinosaurs’ success, and that they didn’t really take off until after the dinosaurs went extinct,” explains David Grossnickle,from the Uiversity of Chicago. “This study shows that therian (daytime active) mammals, the ancestors of most modern mammals, were already diversifying before the dinosaurs died out.

More diversified mammals

The theory that mammals “stuck to the shadows” has been formed from fossil archives.  Several decades ago, the only bones of mammals that were discovered that dated from the period of dinosaurs belonged to insect eating mammals.  However the more that we excavate the more we can find.  As time goes on the more we have come to learn that primitive mammals were more diverse and bigger than previously thought.  After analysing the mammals varied tooth structures it is clear that they had different diets.

The asteroid which caused one of the biggest extinctions ever seen on the planet didn’t spare these mammals either.  The first mammals were also struck by a selective extinction as those with a more general diet could adapt to changes.  Those mammals that “ate everything” would adapt their habits to the changing environment while other species with a more specific diet disappeared.

A study published in the journal called Nature Ecology & Evolution revealed that the first daytime activities of our ancestors happened about 65.8 million years ago.  This would have been some tens of thousands of years before dinosaurs become extinct.   The so-called “night-time bottleneck” hypothesis suggests that dinosaur extinction allowed the mammals to expand, as they were able to look for food during the day. What this new study reveals to us is that this expansion may have taken place earlier than was supposed.

mammifères
Purgatorius Unio, An example of an early daytime active mammal. Credits : Wikipédia

The dinosaurs were already condemned

As mammals started to expand it seems that dinosaurs were already condemned several million years before their extinction.  At least this is what a study, published in 2016 in the Proceedings of the National Academy of Sciences (PNAS) journal suggests.  Several dinosaur species started to disappear more quickly than the appearance of new species.  This means that dinosaur extinction could have started 40 million years before their definitive extinction.

It is difficult to know why mammals diversified before the dinosaurs became extinct.  It could be linksed to the growth of flowering plants which researchers believed developed at the same time. “We can’t know for sure, but flowering plants might have offered new seeds and fruits for the mammals. And, if the plants co-evolved with new insects to pollinate them, the insects could have also been a food source for early mammals,”explains David Grossnickle.

The dinosaurs, who still today reigned the earth for the longest time in comparison to any other animal, didn’t become extinct from one day to the next.  This change from reptiles to mammal seems to have taken some time, between 20 to 40 million years.

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