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Interview: Steve Brusatte on The Rise and Reign of the Mammals - or why Toxodons are awesome

Updated: Jun 20, 2023

We're delighted to welcome back paleontologist and best-selling author Steve Brusatte to the blog! Steve's book 'Rise and Fall of the Dinosaurs' is the best book about dinosaurs I have ever read in the history of my life. FACT. Now Steve has a new book out, 'The Rise and Reign of the Mammals'. Which, quite frankly, looks awesome. Actually, with the book being out today (June 9th date fans) I'm probably reading it right now.

Anyway, we were fortunate enough to get to interview Steve. We have a brilliant chat, Steve is full of phenomenal information. It must leak from his pores like knowledgeable sweat. Which is a pretty gross mental image, sorry about that. Clearly, I'm just excited about getting to read The Rise and Reign of the Mammals. So, no more messing about, let's get to the interview!

Imagining History - Could you tell our readers a little bit about your new book, The Rise and Reign of the Mammals?

Steve Brusatte - This is a book about us. No, not about humans specifically. Humans garner just a single chapter. But it's about our family, the mammals, the wider group of animals to which we belong. Our cousins, our ancestors. It is, I hope, a grand tour of mammalian evolution, beginning 325 million years ago when the mammal line split from the reptile line on the great family tree of life. These proto-mammals went one way, destined to mostly live in the shadows for millions of years. The proto-reptiles went another way, eventually producing dinosaurs and other magnificent beasts whose fossils have hogged most of the attention.

Everybody knows T. rex, Triceratops, Brontosaurus. For most of my career, I've studied these animals, and a few years ago I wrote a pop science book called The Rise and Fall of the Dinosaurs, all about them and their evolutionary story. But my research has drifted, and my attention shifted toward mammals. After all, when the dinosaurs went extinct, it was mammals who (finally) took over. So when it came to writing my next book, mammals were the natural subject.

What was it that inspired you to write a history of our mammal forbears?

Dinosaurs get most of the love. Species like T. rex and Brontosaurus are the most iconic and recognizable fossils of all. Dinosaurs get the prime space in museums, generate the most headlines and viral news stories, and are the stars of the biggest movies. And for good reason - they are awesome. But there is so much more to the history of life. Earth is 4.5 billion years old, after all!

As my research has turned more towards mammals--and particularly, the question of how mammals survived the asteroid that killed the dinosaurs--it surprised me that there haven't been many pop science books on mammal evolution. Sure, there are plenty on *human* evolution specifically, but few on the other 99.9% of mammal fossils and species that are not humans. And even the books on human evolution cower in number relative to those on dinosaurs. I want people to understand our evolutionary story, how our forebears gutted it out for millions of years in the shadows of the dinosaurs, then bested the dinosaurs and took over the world, resulting in the 6000+ mammal species that surround us today. Our pets, the most popular attractions in our zoos, our food, ourselves. And I want readers to revel in the awesome fossils that tell this story. There were once mammals that ate dinosaurs for breakfast, primitive elephants the size of miniature poodles, whales that walked (with their legs, before they turned to flippers), giant ground sloths that could stand so high they could dunk a basketball, armadillos the size of Volkswagens, enormous woolly elephants and rhinos, and dozens of species of extinct fossil humans. These all deserve to be as famous as T. rex and Velociraptor.

Man, I'd love to see a walking whale. I'd bet she would have whale of a time. Thank you. I'm here all day. *cough* Anyway. How do you take such a complicated thing, in this case, the history of 6000+ mammal species, and make it accessible to a general reader?

It's 325 million years of evolution distilled into 10 chapters and about 400 pages of fast-paced text. There was a lot of information to process, and I must say, in the course of researching this book I learned a huge amount about mammals. Frankly, before starting this book, I was a dinosaur paleontologist, pure and simple. I had studied mammal fossils here and there, but I was really a dilettante. Now that I've learned so much about mammals, I wonder why I haven't studied them from the start. So, really, when writing this book I was experiencing mammal evolution in all of its wonders for the first time. And I tried to take that enthusiasm and put it on the page. The book goes chronologically, starting with our distant lizard-like ancestors and ending with the evolution of Homo sapiens and the Ice Age, and the modern world. The narrative is linear, but the book really is two books in one: the first half is all about how our very deep ancestors evolved hair, molar teeth, huge brains, warm-blooded metabolism, the ability to feed their babies milk, and all of the other things that make mammals mammals - but did so while tiny, and living as B-list characters in a dinosaur world. Then the second half is all about what happened after the dinosaurs died and mammals made the world their own--in essence, the evolution of all of the mammals we know and love: dogs and cats, elephants, whales, bats, horses, monkeys, and us. I tried not to make it a dry catalogue of facts, but to use many stories of my own fossil discoveries, the fieldwork of my friends and colleagues, and tales from the history of science to show the reader how we know what we know. And there are lots of illustrations--about 80, including gorgeous cover artwork and chapter-opening mammal species hero shots from Todd Marshall, scientific illustrations of skulls and jaws and teeth and an anatomy from Sarah Shelley, and lots of photos of mammal skeletons, fieldwork, and people who study mammals.

Yes. I love pictures! So, with all the information you discovered, could you tell us a fascinating fact about ancient mammals that will blow our tiny minds?

Here's something we literally just learned; we just published it in April, in a new paper led by my Edinburgh colleague and lab-mate Ornella Bertrand. After the dinosaurs died, mammals actually got dumber. By that I mean, their bodies ballooned in size so quickly (to fill the new niches left vacant by T. rex and Triceratops) that their brains did not keep pace. Their relative brain size (brain compared to body weight) decreased! And we know from modern mammals that intelligence is largely about relative brain size. So although we like to think of ourselves as really smart--and, of course, we are--it wasn't intelligence that allowed our ancestors to wrestle the crown from the dinosaurs.

BOOM! Mind blown. Which was your favourite mammal to research and write about?

One of the stars of my Ice Age chapter is a giant ground sloth called Megalonyx. Today's sloths are cuddly critters that hang from the trees and don't do much else. But a mere 10,000 years ago there were super-sized sloths that weighed a ton and were about 10 feet tall when they stood up. In the late 1700s, some weird bones were found in a Virginia cave, including an enormous scythe-like claw. These caught the attention of a certain gentleman of colonial esteem, Thomas Jefferson. Just a few days after being sworn in as Vice President, Jefferson presented a research paper on these sloth bones to an academic society in Philadelphia. Imagine that - a sitting vice president, just days into their term, going to a scientific conference to present new research. It's unfathomable today.

If I was a Vice President that's totally what I'd do. I'd probably also cry as I'd be the Vice President and that sounds very stressful.

Thanks for that. Back to the story?

Back to the story.

Jefferson at first thought the claw belonged to a colossal American Lion, but later came to understand the bones were from a bizarre sloth. He argued for decades that such creatures must still be alive somewhere out west--and he gave the explorers Lewis and Clark an explicit mission to go find them, on their famous survey of the Louisiana Purchase. Alas, they came back empty-handed, and when Jefferson was close to death he finally admitted that these sloths must have gone extinct. But there is so much more to this story - including President Jefferson using rooms in the White House as makeshift research labs for studying mammoth bones. And, a rarely-told tale of who truly identified the first mammal fossils in America and put their thoughts in writing. It sure wasn't Jefferson; it was a group of enslaved Africans in South Carolina. You'll have to read the book to find out how all of these threads fit together.

Which fascinating mammal featured in your book will we never have heard of?

I hope that my book can help introduce a new slate of spectacular fossil mammals to the public--and maybe help make some of them as famous as woolly mammoths and sabre-toothed tigers. Here is one mammal I would love to see become an icon: Toxodon. It is part of a group of hoofed mammals from South America, which went extinct during the Ice Age, about 10,000 years ago. But their legacy stretches back to about 66 million years ago, right after the dinosaurs died. Indigenous people in South America long ago came across their bones and pondered what they represented. Later, when the Beagle anchored at port, a young Charles Darwin discovered some of their fossils and sent them back to England. These mammals flummoxed Darwin. They seemed like a mishmash of creatures known from other parts of the world. Horses with trunks like elephants and teeth like rodents. Frankenstein creatures. South America was an island continent from the time the dinosaurs died until only a few million years ago when it brushed up against North America and two long-isolated lands and their inhabitants made contact. So these mammals that bewildered Darwin lived in seclusion for tens of millions of years, sequestered from other mammals. They essentially evolved in their own fortress. And what were they? What other mammals were they related to? Where do they fit on the family tree? Nobody knew until a few years ago, when DNA evidence finally revealed the answer, like a paternity test on one of those afternoon television shows. I won't tell you what it is; you'll have to read the book!

Stop teasing me with your book Steve! I just can't take it as I want to read it right now!!! I know, I'll distract you with another question: will scientists one day be able to clone a Woolly Mammoth and, if they could, should they?

I touch on this subject towards the end of the book. It's complicated, both scientifically and ethically, and honestly, this is out of my comfort zone. I'm not a geneticist or a molecular biologist. Still, from everything I've read and learned, it seems like it might be plausible, even probable. It wouldn't surprise me to wake up one morning to the shocking news that a rogue scientist somewhere has cloned a furry little elephant. But as a certain movie character portrayed by Jeff Goldblum would say: that only concerns the 'could', not the 'should'. Is it ethically reasonable to bring back a mammoth - an extinct creature, which lived in a world different from our own? A much colder world, where glaciers stretched from the North Pole down past Chicago and Edinburgh. And then again, humans were probably instrumental in the extinction of the mammoth, so if we could clone it, might we have an ethical duty to right our wrong? Complicated. I have my opinions, but they are not set in stone. I am on the fence here.

Sounds painful, maybe a chair might be better for sitting? Finallly, what are you working on next?

After writing this book and having so much upheaval during the pandemic and recently becoming a father and spending a lot of time caring for my son and watching him grow up, it's back to research. My lab at the University of Edinburgh is studying so many interesting things about mammal evolution, especially those mammals that lived in the Paleocene, the first 10 million years after the dinosaur extinction. We recently published the study on mammal brains I mentioned above. We now have in-progress work on how these mammals grew, and where they are placed on the family tree (how they are related to today's mammals). We do a lot of fieldwork in New Mexico, one of the best places in the world to find fossils of these mammals. And of course, I continue to study dinosaurs and other fossil reptiles, and also to do a lot of consultancy. I was the paleontology consultant for the new Jurassic World film, which is hitting theaters right around the time my mammal book is coming out...

Your mammal book and a new Jurassic World film?! Best. Day. Ever.

Steve, thanks so much for answering my questions. We've done a lot of these interviews now and this is my favourite yet, absolutely fascinating!

To say hello to Steve you can find him on Twitter over at @SteveBrussatte

To check out Rise and Reign of the Mammals, be sure to click here.


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