Prehistoric Mammals: Book Review

Many years ago when I was working at the Aquarium of Niagara I was given a birthday present that was extremely pensive. Shortly after meeting me you will learn that I adore sloths. The educator who gave me this gift took it one step further, when I unveiled a peg-like rock. It had a certificate of authenticity stating that it was non-other than a extinct ground sloth’s tooth! A gift that I had definitely not received before.

Kenny Sloth

After the mass extinction of the dinosaurs 65 million years ago, mammals became the dominant terrestrial life form on our planet. Roaming the earth were spectacular beasts such as saber-toothed cats, giant mastodons, immense ground sloths, and gigantic giraffe-like rhinoceroses. This month The Princeton Field Guide to Prehistoric Mammals will be released which guides you through the lost world of these wonderful, and often times giant, prehistoric creatures.

While a woolly mammoth probably won’t come thundering through your vegetable garden any time soon, you can use this field guide help visualize and classify these extinct mammals. The book covers all the main groups of fossil mammals, discussing taxonomy and evolutionary history, and providing concise accounts of the better-known genera and species as well as an up-to-date family tree for each group. No other book presents such a wealth of new information about these animals—what they looked like, how they behaved, and how they were interrelated. In addition, this unique guide is stunningly illustrated throughout with full-color reconstructions of these beasts—many never before depicted—along with photographs of amazing fossils from around the world.

Author Donald R. Prothero is research associate in vertebrate paleontology at the Natural History Museum of Los Angeles County and professor emeritus of geology at Occidental College. His many books include Greenhouse of the Dinosaurs: Evolution, Extinction, and the Future of Our Planet, Evolution: What the Fossils Say and Why It Matters, and After the Dinosaurs: The Age of Mammals.

“Up-to-date, comprehensive, and very readable. Prothero is a renowned expert in this field, with decades of experience working on diverse groups of prehistoric mammals. He clearly knows his subject well and skillfully conveys this knowledge to readers.”–Spencer G. Lucas, New Mexico Museum of Natural History and Science

The book demonstrates evolution in action, such as how whales evolved from hoofed mammals and how giraffes evolved from creatures with short necks. Author Prothero explains how mass extinctions and climate change affected mammals, including why some mammals grew so huge.


With a  giant sloth being attacked on the front cover, I skipped immediately to the Xenarthra chapter to learn more about ground sloths. I already knew that future president Thomas Jefferson described Megalonyx (“giant claw” in greek) and thought it was a giant lion. I did not know that he thought this animal still existed and that he sent out Lewis and Clark to find this animal in their 1803-05 adventure. As I get older, history is puzzling itself together. Around 20 years later, with descriptions of other fossils including Megatherium did people realize that the claws were from a giant ground sloth – not a lion.

Another new discovery I read was that one genus Thalassocnus was a swimming ground sloth, that was semi-aquatic, with evidence from four successive species showing an increase in density, which would be necessary for a marine mammal. It is thought that they used their long claws to cling on rocks in the surf, much like modern marine iguanas.


Last thing I didn’t realize until I read this chapter was just how large giant ground sloths were. Yes, they have the word giant in their name and yes I have seen two fully constructed ground sloths at the Smithsonian, but some genera were so large that only certain mammoths and gigantic rhinos were larger.

This upcoming book is 240 pages, and contains over 300 color and black and white illustrations. It’s a great read for those looking for clues from the past to help us understand the future of mammals.

Follow the conversation at Critter Companions by Kenny Coogan

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