Therizinosaurus

Life restoration of Therizinosaurus

Therizinosaurus was one of the strangest-looking dinosaurs to ever walk the Earth. Living about 70 million years ago in what is now Mongolia, this giant creature could reach around 10 m in length and around 5 m tall. It had a small head with a beak for cropping leaves, a long neck to reach high vegetation, and a wide, barrel-shaped belly for digesting tough plants. Unlike its theropod relatives, Therizinosaurus was most likely herbivorous.

Currently only one species is known - T. cheloniformis. It belonged to a group called therizinosaurs: a branch of feathered theropod dinosaurs (relatives of birds) that evolved for a plant-eating lifestyle. Imagine a pot-bellied, long-necked animal walking on two sturdy legs with wide, four-toed feet and a backward-pointing pelvis. At the front was a beaked snout with leaf-shaped teeth, and on the arms, three enormous, scythe-like claws. Many therizinosaurs likely had a shaggy coat of simple feathers. Known mainly from the Late Cretaceous of Asia (with some in North America), they looked a bit like "sloth-dinosaurs": heavy-bodied, long-armed, and built for browsing rather than chasing prey.

Physical Characteristics

Size of two Therizinosaurus specimens compared to a human

The most striking feature of Therizinosaurus was its arms, which were about 2.4 metres (nearly 8 feet) long and ended in three flattened claws - the longest claws known from any land animal. Each claw could grow over 50 cm in length. These claws were relatively thin and not adapted for slashing or stabbing. Instead, they were probably used for pulling down branches, for display, or to intimidate predators.

Only partial remains of Therizinosaurus - mainly from the arms, legs, and ribs - have been found, so reconstructions are based on comparisons with related species. It is estimated to have weighed between 5 - 10 tonnes. Its skeleton was partly air-filled to reduce weight, and it likely had simple feathers. Like other therizinosaurs, it walked on two legs and had broad, four-toed feet supporting its massive frame.

Discovery and Classification

Therizinosaurus was first discovered in 1948 during Soviet-led expeditions to the Nemegt Formation in Mongolia's Gobi Desert. Among the fossils found were three enormous hand claws - each over half a metre long - along with bone fragments. These remains, catalogued as specimen PIN 551-483, were described in 1954 by Russian paleontologist Evgeny Maleev, who named the animal Therizinosaurus cheloniformis ("scythe lizard shaped like a turtle"). Maleev believed it was a huge, turtle-like reptile that used its claws to gather seaweed and created a new family, Therizinosauridae, for it.

It wasn't until the 1970s that other researchers recognised Therizinosaurus as a theropod dinosaur rather than a marine reptile. Further discoveries - including partial arms and a four-toed foot - showed clear similarities to other unusual plant-eating theropods such as Segnosaurus. This confirmed that the claws belonged to a large, bipedal dinosaur. Though most theropods were carnivores, Therizinosaurus represented a plant-eating offshoot of this group, closely related to bird-like dinosaurs such as Velociraptor.

Diet and Behaviour

Therizinosaurus is widely thought to have been a large, slow-moving browser that fed mainly on leaves and other soft vegetation. Its long neck and arms helped it reach and pull down branches, while its small head and beak were adapted for cropping plant material. Its wide pelvis and strong legs provided stability, and it may even have leaned back on its hind limbs while feeding to free its arms for foraging.

Biomechanical studies indicate that the claws were too delicate for digging or combat but well suited to a "hook-and-pull" motion - drawing vegetation toward the mouth much like a giant ground sloth. Secondary uses such as display, intimidation, or limited defense are also possible, but their primary role was likely feeding.

Environment

Therizinosaurus lived around 70 million years ago in what is now the Gobi Desert of southern Mongolia. At that time, the region was far greener and wetter than today, with wide river valleys, floodplains, and patches of forest. The climate was seasonal, with warm, rainy summers and cold, dry winters. The landscape supported conifers like Araucarias, along with ginkgos, cycads, and early flowering plants - providing ample food for large herbivores.

The Nemegt ecosystem included duck-billed hadrosaurs, titanosaurs, and the massive, ostrich-like Deinocheirus, as well as oviraptorosaurs, dromaeosaurs, crocodile-like reptiles, turtles, fish, and the apex predator Tarbosaurus. With its height and long arms, Therizinosaurus likely browsed high in the canopy, avoiding much competition and deterring many predators with its sheer size and impressive claws.

Jurassic World Depiction

Cropped, low-resolution screenshot from Jurassic World: Dominion (2022) © Universal Pictures. Used here under fair dealing for the purpose of criticism and review.

In Jurassic World: Dominion, Therizinosaurus is depicted as a blind, highly aggressive animal that kills a Giganotosaurus by stabbing it with its claws. In reality, there is no evidence that Therizinosaurus was blind, nor that it behaved in this way. Its claws, though impressively long, were thin and poorly suited for piercing through bone or muscle.