Tyrannosaurus rex

Tyrannosaurus rex lived about 68 to 66 million years ago on Laramidia, the western part of North America, and its fossils are known from Montana, the Dakotas, Wyoming, Alberta and elsewhere. The best-known skeleton, Sue, found in South Dakota in 1990 by Sue Hendrickson, is about 12.3 m long. An adult weighed perhaps 8 tonnes, with teeth up to 30 cm including the root, and a bite estimated at about 35,000 newtons by Paul Gignac and Gregory Erickson in 2017, the strongest known for a land animal. The two-fingered arms were small, but strong.¹

T. rex was the heir of a long line of tyrannosaurs. Small, feathered early tyrannosauroids lived in the Jurassic, Yutyrannus shows large feathered forms by about 125 million years ago, and giants appeared in the last 20 million years of the Cretaceous. Growth studies of bone rings by Gregory Erickson show teenagers gaining up to about 2 kg a day before reaching adult size at about 18 years. Large nostrils and olfactory bulbs suggest a strong sense of smell, and eyes facing forward gave good depth vision.²³

Healed bite marks on prey and bite marks on T. rex bones show that it was both a hunter and a scavenger, and fought its own kind. Whether small tyrannosaur fossils such as Nanotyrannus are juveniles or a separate species is still debated. T. rex lived through the last stretch of the dinosaur era, and died out when the asteroid struck 66 million years ago.⁵⁶