Steve Brusatte – The Rise and Reign of the Mammals (2022) Review

As a kind of sequel to his previous book, The Rise and Fall of the Dinosaurs (2018), popular science writer Steve Brusatte now looks at the evolutionary history of the mammals. The previous book even ended with a cliffhanger: a giant meteor crashed into the Earth and killed off the Dinosaurs! Oh no! Read on to find out what happened next! Actually, I hear all you science geeks exclaim, ACKshually, you’re pretty wrong there, because (a) dinosaurs still exist in the form of birds, and (b) the story of the mammals doesn’t start with the meteor crash.

That’s exactly Brusatte’s first important point. This book doesn’t start the timeline at the meteor crash but way before, before the Dinosaurs, in the late Carboniferous and early Permian, where the lineage of four-footed animals split in two. One lineage evolved into reptiles and dinosaurs, the other into proto stem-mammals and eventually into real mammals. The first real big apex predator of the time, Dimetrodon, a creature often included in the plastic dinosaur collections in toy stores, was a stem-mammal and not a dinosaur. Later on, the Dimetrodon descendants became small furry mousy creatures while the dinosaurs took over the apex predator niches, and the mammals had to wait for better times to grow big again.

The cool thing about following the evolution of the mammals is that we can trace the development of parts of our own bodies. Something we could not do with the story of the dinosaurs. Even if it is just about small things like the development of our jaw bones, these structures go all the way back to before the dinosaurs and it is interesting to read the up-to-date explanations as to why they developed in the first place. Why, for example, did mammals get a hard roof in their mouth and many reptiles didn’t? (So that we can suck in more oxygen while chewing.) It makes you wonder about your own body and why it ever got shaped the way it is. Some random features have functions that go back a hundred million years and were hip stuff at the time.

From the perspective of a reptile or a dinosaur, mammals are hypercharged vermin. Everything in our physiology, from the hair and the warm-bloodedness to the mammary glands and the shape of our jaws, is optimised for fast and huge food intake, high metabolism, fast growth, high adaptability to climate and big brain support. It’s true that the dinosaurs kept us from becoming big, but the mammals also kept the dinosaurs from becoming small. Nobody could compete with the mammals at sizes between mouse and badger. We were too fast, too adaptable and too clever.

Let’s be honest, half of this book is a story about molars. Brusatte does his best to make his writing interesting by giving us anecdotes about digging up fossils and life as a palaeontologist, but all his stories are about digging up teeth. Since that is most of what we found of early mammal lineages, these animal groups are all named after their dental situation. Not very exciting. Only when the mammals grew big and radiated in diversity did they get more spectacular, but that’s later in the book. 

But that’s the stuff I always wanted to read about ever since I was a kid. Dinosaurs are great, but there have also been big and crazy mammals that never really got their moment of fame. There were huge and strange types of mastodons and rhinos and sloths that deserved to be mentioned. And there have been interesting evolutionary stories to tell, such as the development of grass and what that meant for the ecosystems of the world, and the evolution of horses and savanna species that came with grasslands and the Ice Age animals and, ultimately, us. This book delivers much of that, once you get past all those molars. 

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