The passing of the age of the dinosaurs allowed mammals to become ascendant. But mammals have a much deeper history. They - or, more precisely, we - originated around the same time as the dinosaurs, over 200 million years ago; mammal roots lie even further back, some 325 million years. Over these immense stretches of geological time, mammals developed their trademark features: hair, keen senses of smell and hearing, big brains and sharp intelligence, fast growth and warm-blooded metabolism, a distinctive line-up of teeth (canines, incisors, premolars, molars), mammary glands that mothers use to nourish their babies with milk, qualities that have underlain their success story. Out of this long and rich evolutionary history came the mammals of today, including our own species and our closest cousins. But today's 6,000 mammal species - the egg-laying monotremes including the platypus, marsupials such as kangaroos and koalas that raise their tiny babies in pouches, and placentals like us, who give birth to well-developed young - are simply the few survivors of a once verdant family tree, which has been pruned both by time and mass extinctions.

Professor Steve Brusatte is a palaeontologist on the faculty of the School of GeoSciences at the University of Edinburgh in Scotland. He grew up in the Midwestern United States and has a BS in Geophysical Sciences from the University of Chicago, a MSc in Palaeobiology from the University of Bristol (UK), and PhD in Earth and Environmental Sciences from Columbia University in New York. Steve is widely recognized as one of the leading palaeontologists of his generation. His 2018 book, The Rise and Fall of the Dinosaurs, was a Sunday Times bestseller, and he is the science consultant for Jurassic World 3, the third film in the Jurassic Park franchise.