So many books have been written about dinosaurs, but this one looks at a deeper history of another important group: our own. Beasts Before Us is “the untold story of mammal origins and evolution.” The Cenozoic is often dubbed “the age of mammals,” but the story of our hairy, milk-guzzling brethren goes much deeper into geologic time. There have sort of been two ages of “mammals,” author paleontologist Elsa Panciroli points out. The first was in the late Paleozoic, when the terrestrial realm was “dominated” by synapsids. Ultimately, these animals were ancestral to the line of evolutionary descent that became mammals. They were their own entity, though they are often dubbed “mammal-like reptiles,” Panciroli makes the case that “reptile-like mammals” might be a better descriptor. I really enjoyed the deep, detailed discussion exploring the various proposed explanations for the sails on the backs of certain synapsids, such as Dimetrodon and Edaphosaurus. Were they for thermoregulation, fat storage support, sexual display, or defense? Panciroli explores the pros and cons of each idea. It was refreshingly robust. She follows the evolutionary story into the Mesozoic, when crocodilians and then dinosaurs “take over” the land, but mammals and their ancestors were surprisingly common and diverse, if not as robustly represented in the fossil record. Panciroli relates tales of her research in various parts of the world, but particularly on the Isle of Skye in Scotland. Her perspective is fresh and enthusiastic, which helps compensate for the (to me) bewildering array of paleontological and anatomical jargon. The book is infused with a social and political perspective that could be dubbed “woke,” with significant attention paid to the colonialism, racism, and sexism that unfortunately permeated paleontology’s earlier years, and whose legacy haunts us still. She also devotes book-conclusion attention to what may be the most significant aspect of mammal evolution – that one of their species has rapidly transferred a large portion of the planet’s fossil carbon back into its atmosphere, with effects that will be felt all over the planet for a long time to come. There were a few small errors that better editing would have caught – substituting “Mohican” for “Mohawk,” for instance. Another that will rankle geochemists is abbreviating uranium as “Ur” rather than “U.” I read the first edition, hardcover, so that sort of thing may be cleaned up in subsequent printings.