Dinosaurs and Mammals After Asteroid Collision: Links Expert Explains

Professor Brusatte, when do early mammals appear and how should we perceive them?

This depends on the definition of “mammal”. There are always scientific discussions on this topic. The traditional definition considers them to be the first animals to have a joint between the dentin of the lower jaw and the scales of the upper jaw. These early mammals appeared about 230 to 220 million years ago. Animals such as Morganucodon are small and agile, reminiscent of small mice or hamsters. Their home is a world where dinosaurs are just beginning to appear.

Small, like a mouse and in the shadow of a dinosaur: this fits the common picture of early mammals. Is this picture still correct?

No, even in the time of the dinosaurs, mammals were a very diverse group, perfectly adapted to their stature. One thing is true: During the more than 100 million years they have lived with dinosaurs, they have remained young. They are never larger than a badger. Dinosaurs kept them small, and mammals kept dinosaurs large.

Profile: Steve Brusatte is Professor of Paleontology at the University of Edinburgh. He specializes in the anatomy, genealogy, and evolution of carnivorous dinosaurs such as tyrannosaurus. His book The Rise and Fall of the Dinosaurs was a bestseller and was a science advisor for the upcoming Jurassic World movie. His new book, The Rise and Reign of the Mammals, will be published in English in June.

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How was your daily life under the dinosaurs?

Mammals weren’t a boring celebrity back in the days of the dinosaurs. They have lived all over the world and have shown tremendous diversity. There were mammals that sped up on the ground, others burrowed, climbed trees, swam, and even climbed through the air with their wing membranes. Some ate insects, others seeds and plants, and still others ate small dinosaurs for breakfast like the ribinomamus found in modern China. Most of them were probably nocturnal in order to avoid the larger dinosaurs, which not only preyed on them, but also literally trampled on them.

Scientific interest in early mammals increased, as did knowledge about them. what is the reason?

New and very special fossil discoveries from China, especially from Liaoning Province in the northeast. New discoveries are made there every month, mostly by farmers working in the fields. Among them are complete skeletons with preserved hair. These discoveries revolutionized our view of early mammals.

What evolutionary development did mammals go through while living alongside dinosaurs?

During the Triassic, Jurassic, and Cretaceous periods, mammals developed most of the distinctive and somewhat successful traits that make them mammals today. In other words: During this time, our ancestors developed the mammalian schema, the structure of the mammalian body. Hair, large brains, strong sense of smell and hearing, teeth divided into molars, incisors and canines, the ability to feed their children’s milk.

66 million years ago, the age of the dinosaurs ended with the impact of a massive asteroid. How do mammals live?

Mammals almost disappeared with dinosaurs. We estimate that only about 10 percent of them survived the impact. It is assumed that these were mainly small mammals that could feed on very different things and could dig. These qualities proved particularly useful, in part because the world descended into chaos so quickly after the asteroid impact.

There were earthquakes, massive fires, and tsunamis. The sun has hidden behind dust and ash for years, and temperatures have dropped dramatically. Hiding in caves and carnivores was a good survival strategy. Perhaps many animals were lucky.

How quickly can biodiversity recover?

Very fast. In the more than 100 million years that lived alongside dinosaurs, mammals have never grown larger than a badger. Once the dinosaurs are gone, pig-sized animals appear within a few hundred thousand years. Only a million years later, mammals the size of cows existed. This rapid evolutionary progression shows how quickly the remaining mammals have filled the resulting niche and made the world their own.

What new species are emerging?

A particularly interesting group is the placental mammals. These are the ones who, like us, give birth to lively, well-developed babies. These are our ancestors and relatives who began diversifying after the mass extinction. However, many of these ancestors were quite bizarre in appearance and had little in common with modern species. They were plump, muscular and small brains. They had not yet fully adapted to the new world. This will take a few million years.

Can we identify the ancestors of early humans during this period?

The first monkeys, called Plesiadapiformes, appear shortly after the asteroid impact. Exciting fossils have been found in Montana. Its name is Purgatorius and it appeared tens of thousands of years after the end of the dinosaurs. It seems that our ancestors came out of the earth like a phoenix.

It was amazing how quickly mammals diversified. And it shows that if the asteroid hadn’t hit, and if the dinosaurs had never died, we probably wouldn’t be here to have this conversation. Our ancestors, the primates, didn’t get their chance until the dinosaurs became extinct.

Would mammals have replaced the dinosaurs without a mass extinction?

This is one of the greatest “what if” questions of prehistoric times. But I don’t think so. Dinosaurs evolved well over 150 million years ago. They survived and endured a lot: periods of rising and falling temperatures, rising and falling sea levels, volcanic eruptions. If the asteroid had not hit, I think the dinosaurs would have continued to adapt.

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