April 5, 2023 Scott Kraus

Therizinosaurus was a Large Maniraptoran Theropod with Huge Claws

Therizinosaurus was an advanced herbivorous maniraptoran theropod, originally thought to be a strange sauropod, with a mix of both sauropod and theropod characteristics. These characteristics along with its large claws makes it rather unique and much of an oddity. The name Therizinosaurus, (pronounced Ther-uh-Zeen-oh-Sawr-us) comes from the Ancient Greek language and means scythe lizard or reaping lizard.

Therizinosaurus lived during the late Cretaceous period 70 million years ago and was one of the largest and also the last of its family group, Therizinosauria.  One of the most unique looking beasts of prehistoric times, Therizinosaurus has given its name to a whole family of rather bizarre dinosaurs, the therizinosaurs which were previously known as segnosaur.

Quick Facts

What Did Therizinosaurus Look Like?

Palaeontologists don’t know for sure what this dinosaur looked like having recovered few remains for it but, based on other members of the Therizinosauria family it is thought that Therizinosaurus had a small head with beaked skull on a long neck. It is most likely that Therizinosaurus stood upright on two large muscular hind legs having four toes on each bird-like structured foot to bear the weight of its body. Therizinosaurus had a heavy and broad body with a pot belly and a short tail.

It is a known fact that Therizinosaurus had long arms measuring 8.2 feet long with a gigantic claw on each of its three-fingers which could measure up to 3.3 feet in length. These claws, including horn sheath, were approximately the length of a humans arm.

Since the discovery of its close relative Beipiaosaurus which showed protofeathers (precursors of bird feathers) in its fossils it is thought that Therizinosaurus may have been feathered too – though no evidence of this has yet been found.

It has been estimated by paleontologist Gregory Paul that the maximum size of Therizinosaurus would have been 33 feet in length with a height of roughly 9.8 feet weighing 5.5 tons making Therizinosaurus the largest of the Therizinosaurs as well as Maniraptorans.

Physical Attributes of Therizinosaurus – The Claws

Its distinctive giant claws are the longest known from any animal in history and must have made a fearsome sight. Relatively straight, the narrow and transversely flattened, the claws gradually tapered into a point at the end. It is not known exactly what these claws were used for or why they were so long, though it is thought they could have been used to fend off predators such as the 39 foot long Tarbosaurus as well as perhaps during intra-specific battle when males would fight for territory during the mating season as well as to show reproductive maturity via the largest claw.

Recently it has been said that Therizinosaurus was a gentle-giant rather like the modern day Panda and that it would have used its claws simply to assist in feeding. Using the claws to pull down branches and to strip bark off of trees. Some palaeontologists think that Therizinosaurus also used its claws to climb trees to collect fruit and leaves much like the modern day sloth – although though it would have been far too heavy to reach any great height.

What did Therizinosaurus Eat?

It’s unknown what Therizinosaurus ate since no skull and teeth have been discovered to date, however it is thought that this dinosaur was not a carnivore and like other Therizinosauria it was primarily a herbivore.

Some palaeontologists have speculated that Therizinosaurus could have ripped open giant termite nests with its giant claws making it an insectivore, but it seems unlikely that a dinosaur the size of Therizinosaurus would have been able to live off of a diet of insects alone.

Other members of Therizinosauria had leaf shaped teeth with some palaeontologists believing they had beaks used for either stripping vegetation from branches or snapping twigs and branches. The large claws and long arms would have been used to pull the branches down to its beak or to strip bark off of trees as previously mentioned.

How did Therizinosaurus Move?

It is believed by palaeontologists that Therizinosaurus was bipedal, walking upright on its two back legs. However due to the strange shape of its body and large pot belly (most common in quadrupedal sauropods) some people think that Therizinosaurus switched between bipedal and quadrupedal movement, but this would have been problematic due to the large claws on its forelimbs.

It is not known if it was possible for Therizinosaurus to run or at what speed, though it is thought Therizinosaurus must have been a slow-moving dinosaur due to its large claws. In the same way that humans shouldn’t run with scissors it’s thought that Therizinosaurus wouldn’t have run with its claws as one trip would have resulted in a fatal accident.

Where did Therizinosaurus Live?

70 million years ago Therizinosaurus lived in the forests of Asia in what is now the Gobi Desert in Southern Mongolia. This area during the Cretaceous period had contrasting conditions, the forest areas would have been warm and wet though much of the total area would have still been desert or at the very least a very dry habitat with sub-tropical tendencies.

The Discovery of Therizinosaurus

Few fossils have been found for Therizinosaurus meaning little is known about this dinosaur and as such it has caused much confusion to paleontologists for several years. Only the gigantic hand claws and parts of the pelvis, forelimbs and hind-limbs have been discovered so far. Without skull remains palaeontologists are left with a lot of unanswered questions and have had to base much of Therizinosaurus physical characteristics on related Therizinosauria and similarly sized dinosaurs contemporaries.

Therizinosaurus fossils were first discovered in 1948 in the Nemegt Formation of the Gobi desert in Mongolia. 3 giant sickle-like claws were discovered by palaeontologists on a joint Soviet-Mongolian fossil expedition. Because of the shape of the claws, similar to those in some turtles and because the claws were found with large, flat bones, palaeontologists originally thought that this was some sort of turtle-like creature. For this reason it was given the species name of T. cheloniformis meaning “turtle-formed” by Evgeny Maleev, a Russian paleontologist, in 1954.

It wasn’t until a few years later after part of a huge forearm was discovered (originally attributed as belonging to Deinocheirus) that it was realized that this was no ancient turtle but a theropod dinosaur, one of the strangest to have ever lived.

Subsequent finds in the 1990’s of related species; Alxasaurus and Beipiaosaurus have helped to clarify the position of the Therizinosauria as a whole. New research shows that though this dinosaur was once thought to have been a vicious carnivore it was actually a rather docile creature – something atypical of large carnivorous dinosaurs.

The Importance of Therizinosaurus

Therizinosaurus is a unique discovery as an herbivorous maniraptoran theropod with unique long claws. Despite palaeontologists not knowing the exact reason why this dinosaur had such long claws, it is known that they would have evolved for a reason whether that be for foraging or defense helping palaeontologists to understand the evolution of dinosaurs.

Currently Therizinosaurus is a rather elusive dinosaur, but it is hoped that in the future remains of a more complete Therizinosaurus skeleton will be found. This will enable paleontologists to piece together what Therizinosaurus really looked like and its true place within dinosaur society.