An illustration of an extinct giant ground sloth.

It is a problem. There have been many changes in the universe and on our planet. The mass death of the dinosaurs and other creatures in the wake of an asteroid impact 66 million years ago was one of the most recent major changes.

After the impact, mammals were able to grow larger and evolve in ways they couldn't before. The mammals have made more sweeping changes to the planet than any other creatures before.

We don't know how we got here. Steve Brusatte is an Evolutionary Biologist at the University of Edinburgh. He is the author of a new book about the evolution of life in mammals. The Rise and Fall of the Dinosaurs was written by Brusatte. We lightly edited our conversation to make it clear.

Is it a simple question or the most complicated one? This is a book that should be written.

Steve Brusatte said, "Well, I did one on dinosaurs, what am I going to do next?" I will do it on animals. I studied the evolution of birds from dinosaurs and the extinction of the dinosaurs while I was a dinosaur specialist. The next step was to think about what happened after the dinosaurs. The world changed how. It is mammals.

The more I study mammals, the more I realize how fascinating they are and how much the story of mammals is ours. Dinosaurs are awesome, but they are not like alien creatures. Birds and mammals are not the same thing. Our deepest ancestry has produced us and many other mammals today.

The K-Pg extinction is covered in your book. The way the public thinks about those intervening millions of years was something that you were trying to address.

There is a misconception that dinosaurs had their time, they thrived, and they died out, and mammals took their place. Dinosaurs were the top animals on land. Many people don't know that mammals and dinosaurs go back to the same place. The groups started about 200 million years ago on the supercontinent Pangea.

The dinosaurs were going to have a lot of power. Some of them were large. The mammals were kept out of the sunlight. They could not get large. Dinosaurs had the resources and the environment. For over 150 million years, mammals and dinosaurs lived side by side. There were a lot of species of mammals during that time. They were scurriers and climbers. The people glided on their skin. Dinosaurs were eaten by mammals for breakfast. There is a mammal with dinosaur bones in it's stomach.

Pleistocene animals roam on the book's cover.

If you were around then, you wouldn't notice the mammals because they were mostly nocturnal. In the shadows, they were changing. They had to adapt. They were evolving as mammals and their ancestors were trying to survive in the dinosaur-dominated world. I want that to be understood.

Then the asteroid. Dinosaurs are dead. Some mammals are able to adapt due to their smallness. We have a new world.

Someone reading this has at least one adaptation, but they don't think about much, that's crucial for the way that they experience life

The ancestors had a lot of bones in their jaw. There is a lot of bones in the dinosaur's jaw. The only thing mammals have is a single bone and all of our muscles attach to it. The jaw of our mammal ancestors was simplified as they evolved.

There was more than one extra bone. What should they do with them. When things disappear in evolution, some of the bones stay around, but they take on a different purpose. They were smaller than a piece of rice. They moved into the ear to amplify and send sound from the eardrum to the cochlea. Our ancestors used to have ear bones.

This is what allows animals to hear. mammals hear very well We have a great sense of hearing compared to birds or lizards or snakes because of the extra bone that comes from our jaw. When we are in the womb, the bones that are attached to our jaw begin to shrink and move up into the ear It is a great evolutionary story.

The story that you tell in your book was shaped by recent academic scholarship.

An ancient monkey fossil.

A lot of recent science is in the book. Entire ecosystems were buried by volcanos from the same place where the feathered dinosaurs were preserved. These little mouse and rat-sized things are only preserved as fossils because they were locked in so many fossils. That has completely changed our understanding.

The early mammals that lived with the dinosaurs were thought to be dull and dreary. They were all small and generalized. They couldn't do much, so they're eking out their existence in the undergrowth. They took on those small niches. That is a single example.

There's a lot of new evidence in the book. For hundreds of years, some fossil mammal groups have been puzzling. There are mammals in South America. They don't live anymore, but they're weird. They're very large. In South America, Indigenous people encountered their bones. Darwin didn't know what to do with the fossils he collected when the Beagle dropped anchor. He sent them to the other side of the world. They were a weird kind of monster mash-ups, you know, a little bit of a horse, a little bit of an animal. South America used to be an island of its own.

These are things. We didn't know we had a father until a few years ago when someone pulled out the genetic information from the fossil bone and put it in our genes. These things are part of the horse group. They are odd- toed hoofed mammals. The revolution in genetics has given us a better understanding of mammals. It would have been difficult to write this book a decade or two ago.

A herd of modern horses.

Do you like the time in which mammals quickly evolved, or the time in which they began to grow?

We don't know a lot about the mammals that lived in the Paleocene Period after the asteroid. They have a lot of fossils, but they are very puzzling. We can tell that they are mammals that give live births to young people. It's difficult to figure out where they fit on the family tree. These fossils have been known for a long time, and they are the key to understanding how mammals survive the extinction and how they spread after.

In New Mexico, I do a lot of field work with my students, and my colleagues are looking for the fossils of these mammals. Every new fossil gives us a clue as to what these animals were like, who their relatives were, or if any of them were early cousins of ours. After the dinosaurs were gone, they took on the world as their own and stared down the asteroid. There is a chance that mammals could get larger. During the previous 150 million years, mammals were smaller than badgers, but within a hundred or 200,000 years, they were larger than pigs.

An illustration of the elephant-like Deinotherium.

There were some challenges faced by mammals after the K-Pg extinction. Our current period of mass extinction compares to those challenges.

Since the asteroid hit 66 million years ago, there have been a lot of changes to the Earth. For a long time after the asteroid, temperatures were very hot. It had been a long time since the Earth had been so hot. There were global warming spikes and mammals had to adapt, but then the Earth started to cool down. That changed the environment as well. There used to be a lot of jungle. Grasses came in that place. Grasses began to spread around the world about 20 million years ago. Animals have been along for the ride. They had to adjust to the weather. mammals diversified

What is the strangest species that isn't anymore? What should we be angry about?

If we didn't find extinct mammals as fossils, we'd never know they were amazing. These things are called chalico theres. They resemble a gorilla and a horse. The hoofed mammals are extinct, but they walked on their hands. Recently, they died out. Some of our ancestors might have seen them. Today, there is nothing like them. They would be the most popular exhibit at zoos if they continued to persist.

There are some animals that are still with us. The blue whale is the biggest animal that has ever existed, and the biggest organisms that have ever existed on the planet. It is still going strong. The thing is larger than a basketball court. The weight is over 100 tons. It can dive to depths of thousands of feet and its babies are the size of steamboats. We can imagine an alternate reality where blue whales are extinct and all we have are petrified bones. In that kind of world, whales would be as famous as any dinosaur. Let's make sure we save them.

The skull of a glyptodont found in Venezuela.

Is there anything you want people to know about your book?

Brusatte wants people to see the book as a story of us, but also of our evolutionary history. Humans only show up at the end. It's not a book about humans, but a book about all mammals, and it makes us think. We are one of a number of mammals that have evolved over time, from bats and whales to elephants and dinosaurs. It isn't all about us. Our intelligence, consciousness, and ability to work in groups are some of the things that make us a particularly wonderful species. These things allow us to have both good and bad impacts on our planet. The mammals that most affect and harm other mammals are the ones that make us the most dangerous mammals. These talents may save us. We have the option of changing.

You worked on the newest movie in the series. Are there any mammals that we will be lucky enough to see in the film?

The first movie in the series was watched by my father and brothers. I was young at that time. The dinosaurs were very realistic, unlike the images in the books in the library. It's hard to believe that it's been 30 years since the fifth film. My role was to help people. I answered any questions that the director, the character designers, and the artists had. The facts about dinosaurs were mostly about how big they were and how they behaved. The real science was always in the ear of the people who made the movie. They wanted to make sure that the real science was taken into account when designing their monsters.

There are two mammal ancestors and proper feathered dinosaurs for the first time in the series. There are two early synapsids that gave rise to mammals. I am looking forward to seeing these mammals get their due.