Small, shrew-like mammals scurry around the skeleton of a Triceratops at the end of the Age of Dinosaurs. By the time the dinosaurs became extinct, several different groups of mammals had already evolved around the world. The first mammals evolved during the Late Triassic Period. They were furry, warm-blooded animals that probably laid eggs. But while dinosaur predators were about, most mammals remained tiny, shrew-like animals, venturing out of their burrows only at night. The extinction of the dinosaurs enabled mammals to become the dominant land animals. The period after the extinction of dinosaurs, known to scientists as the Palaeogene Period, is sometimes known as the Age of Mammals—although birds also developed into a wide variety of species, including some terrifying predatory giants.
Geological time scale
Geological time scaleAfter the dramatic extinctions at the end of the Cretaceous Period, 66 million years ago, the Earth entered what is known as the Palaeogene Period. Until recently, geologists referred to the time after the Cretaceous as the Tertiary Period, but this has now been divided into two and renamed the Palaeogene Period, comprising the Palaeocene, Eocene and Oligocene epochs, and the Neogene Period, comprising the Miocene and Pliocene epochs.
Paraceratherium was the largest land mammal of all time. This prehistoric rhinoceros measured 8 m (about 25 ft) from head to tail and stood around 5 m (16 ft) tall at the shoulder.
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