Episode 461: Therizinosaurus and Its CLAWS

Further reading: Study: Giant Therizinosaurs Used Their Meter-Long, Sickle-Like Claws for Display Show transcript: Welcome to Strange Animals Podcast. I’m your host, Kate Shaw. I am delighted to report that Therizinosaurus lived in what is now Mongolia in Central Asia, in the Gobi Desert. 70 million years ago, the land wasn’t a desert at all but a forest with multiple rivers and streams flowing through it. Lots of other dinosaurs and birds lived in the area, including a tyrannosaurid called Tarbosaurus that was probably the only predator big enough to kill Therizinosaurus. When the first Therizinosaurus fossils were discovered in the 1950s, they were initially thought to belong to a type of giant turtle. Later it was reclassified as a sauropod relation, not a turtle. These days, we know for sure it’s not a turtle and we’re pretty sure it’s not anything like a sauropod. The Therizinosaurus fossils found so far are incomplete. All we have are some ribs, one hind foot, and mostly complete arms and hands. We don’t have any parts of the skull or any vertebrae, so paleontologists still have a lot of questions about what Therizinosaurus looked like and how it lived, although we have more complete specimens of some of its close relations to help scientists make good guesses. Luckily we have its hands, because its claws are enormous. Therizinosaurus had claws bigger than any other dinosaur known. Therizinosaurus was a big dinosaur overall, with an estimated length of 33 feet, or 10 meters, although until a more complete specimen is discovered we can’t know for sure how big it really was. It may have stood up to 16 feet tall, or 5 meters, and walked on its hind legs. It’s classified as a theropod these days, a group that includes famous dinosaurs like T. rex and Spinosaurus, but it wasn’t closely related to those big fast meat-eaters. Most paleontologists think Therizinosaurus ate plants, but again, we don’t know for sure since we don’t have any of its teeth to examine. Its closest relatives were herbivorous but its immediate ancestors were carnivorous. If Therizinosaurus was a plant-eater, why did it have such enormous claws? Its claws were seriously terrifying! Its arms were big and strong in general, measuring about 8 feet long, or 2.5 meters, including long, slender fingers, and the claws measured over three feet long! That’s more than a meter long. If the claws were covered with a keratin sheath, which is probable, they would have been even longer when Therizinosaurus was alive. They were relatively thin and straight with a curve at the end. There are many reasons why an animal develops big claws. Predators need claws to help grab prey or tear meat into pieces, or an animal may need big claws to help it dig or climb trees. Claws are also great for defense. Some animals use claws to grab tree branches and bend them closer to the animal’s mouth, which is something that giant ground sloths probably did, at least sometimes. The new study published in February 2023 examined the claws of Therizinosaurus and lots of other dinosaurs to learn how strong they were. The claws were 3D scanned, and then the scans were used in various models that measured the stress placed on each claw in various different activities. The study discovered that the claws of different dinosaurs were strong in different ways depending on what they were used for, which wasn’t a surprise. What was a surprise was that Therizinosaurus’s claws were weak no matter which model the scientists used. In other words, Therizinosaurus probably didn’t use its claws to fight other dinosaurs unless it just had to, because they would break too easily. It wouldn’t have dug with its claws or even used them to hook branches down closer to its mouth. As far as we can tell, its claws were basically useless. But obviously, Therizinosaurus used its claws for something or it wouldn’t have evolved to have such gigantic claws. The study concluded that the giant claws must have been for display, to attract a mate or maybe just scare off potential predators. Lots of animals have special features used to attract a mate, like a peacock’s tail. Sometimes these features serve a double purpose, like a male deer’s antlers. The size of the antlers show how healthy he is, and he also uses them to fight other males. I’m not a claw expert, but as far as I know there aren’t any other animals known that use their claws for display only. It’s possible that Therizinosaurus did use its claws for something else, we just don’t know what. It’s also possible that the study had flaws that a follow-up study will discover, and Therizinosaurus’s claws weren’t actually so weak. But for now, as far as we know, during mating season Therizinosaurus would strut around waving its super-long claws to show how amazing it was. And, let’s face it, Therizinosaurus really was amazing. Thanks for your support, and thanks for listening!