Therizinosaurus

Chapter • Meet the dinosaur

Overview

Therizinosaurus was one of the strangest dinosaurs ever to walk the Earth. It belonged to the theropods – the same branch that produced Tyrannosaurus and modern birds – yet it looked nothing like a typical predator. Picture a barrel-bodied biped with a long neck, a small beaked head, unusually broad hips and a dense coat of shaggy, hair-like feathers. Its signature feature was its hands: the bony core of the longest claw reached roughly 50 centimetres along the outer curve, making them the longest claws known from any land animal in Earth's history. The animal grew to about 9–10 metres long, could reach 4–5 metres up into the trees and weighed an estimated 3–5 tonnes. Despite those fearsome hooks, Therizinosaurus was almost certainly a plant eater. Its jaws were weak, the front of the snout carried a horny beak, and the teeth were small and leaf-shaped – ideal for cropping foliage rather than slicing flesh. The unusually wide pelvis housed a large gut where tough vegetation could ferment slowly. Palaeontologists compare its arms to those of giant ground sloths and anteaters: tools for hooking branches and pulling them down to the mouth, and a formidable deterrent against predators such as Tarbosaurus, which shared its landscape. Like other theropods it walked on two legs, with the body balanced roughly horizontally over the hips, but it carried its neck raised in a swan-like curve. The tail was short by theropod standards and never dragged along the ground. This was no sprinter: heavy limbs and a bulky belly point to a slow, deliberate browser that relied on size and claws rather than speed. The first fossils were collected in 1948 by a Soviet–Mongolian expedition in the Gobi Desert and described in 1954 by the Russian palaeontologist Evgeny Maleev. Working only from gigantic claws and fragments of forelimb, he concluded that they belonged to a huge turtle-like reptile that raked up seaweed – hence the species name cheloniformis, "turtle-shaped". Only in the 1970s, as more therizinosaurs came to light, was the animal recognised as a theropod. Better-known relatives such as Nothronychus, Beipiaosaurus and Segnosaurus now allow us to reconstruct what Therizinosaurus really looked like.

Chapter • Where it lived

Habitat

Therizinosaurus lived roughly 72–68 million years ago, during the Maastrichtian stage at the end of the Cretaceous. All confirmed fossils come from the Nemegt Formation of southern Mongolia, in what is now the Gobi Desert. Back then the region was not a desert at all but a lush, seasonally wet floodplain crossed by wide river channels, with sandbars, lakes, marshes and forests of conifers, ginkgoes and ferns. A long-necked browser could feed both in the shrub layer and high among the branches. Its neighbours included Tarbosaurus, Deinocheirus, Nemegtosaurus, Saurolophus and Prenocephale.

Chapter • Wild behavior

Behavior & Ecology

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Chapter • Scientific place

Taxonomy