In most accounts, the story of mammal evolution starts after the asteroid impact that killed the non-bird dinosaurs, but in the last 20 years scientists have uncovered new fossils that have drastically rewritten this story. Drawing on her new book Beasts Before Us, paleontologist Elsa Panciroli goes back 300 million years earlier as she discusses the emergence of the extraordinary lineage to which we belong, called Synapsida, from their murky split from a shared ancestor with reptiles at the dawn of life on land.

The synapsids made the world theirs long before the rise of dinosaurs. New fossil discoveries from South Africa, China, and Scotland are being made by an increasingly diverse community of scientists using cutting-edge visual technologies such as synchrotron X-ray scanning.

They are transforming what we know about familiar beasts like the sail-backed Dimetrodon—which belongs to our family tree—as well as introducing us to new and astonishing creatures. These include sabre-toothed hyper-predators and armored plant-eaters, many of which pioneered ways of life that underpin the food webs of the modern world. Alongside the dinosaurs, ancient mammals shrank in size, but far from being overshadowed, it was this evolutionary innovation that unlocked the biological traits that define mammals as we know them today.

Panciroli is a researcher and writer based at the University of Oxford Museum of Natural History. Beasts Before Us (Bloomsbury Sigma) is available for purchase.

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