10 Facts About Therizinosaurus, the Reaping Lizard

With its three-foot-long claws, long, garish feathers and gangly, pot-bellied build, Therizinosaurus, the "reaping lizard," is one of the most bizarre dinosaurs ever identified. Discover 10 fascinating Therizinosaurus facts.

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The First Therizinosaurus Fossils Were Discovered in 1948

Therizinosaurus Dinosaur Side Profile
CoreyFord / Getty Images

Before the Second World War, the interior of Mongolia was accessible to (though not easily traversed by) pretty much any nation with sufficient funding and interest—witness the trailblazing 1922 expedition of Roy Chapman Andrews, sponsored by the American Museum of Natural History. But after the Cold War was in full swing, in 1948, it was up to a joint Soviet and Mongolian expedition to excavate the "type specimen" of Therizinosaurus from the famous Nemegt Formation in the Gobi Desert.

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Therizinosaurus Was Once Thought to Be a Giant Turtle

Green Sea Turtle, Raja Ampat
Daniela Dirscherl / Getty Images

Perhaps because Russian scientists were increasingly isolated from the west during the Cold War, the paleontologist in charge of the 1948 Soviet/Mongolian expedition described in the previous slide, Yevgeny Maleev, made a colossal blunder. He identified Therizinosaurus (Greek for "reaping lizard") as a giant, 15-foot-long marine turtle equipped with giant claws, and even erected an entire family, the Therizinosauridae, to accommodate what he thought was a unique Mongolian branch of sea turtles.

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It Took 25 Years for Therizinosaurus to be Identified as a Theropod Dinosaur

Illustration of Segnosaurus walking into water
Segnosaurus. DEA PICTURE LIBRARY / Getty Images

It's often the case that a bizarre fossil discovery, especially of a 75-million-year-old dinosaur, can't be fully understood without additional context. While Therizinosaurus was finally tagged as some kind of theropod dinosaur in 1970, it wasn't until the discovery of the closely related Segnosaurus and Erlikosaurus (from elsewhere in Asia) that it was finally identified as a "segnosaurid," a bizarre family of theropods possessing long arms, gangly necks, pot bellies, and a taste for vegetation rather than meat.

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The Claws of Therizinosaurus Were Over Three Feet Long

Therizinosaurus hand and claws

 Woudloper/Wikimedia Commons/CC BY-SA 3.0

The most striking feature of Therizinosaurus was its claws—sharp, curved, three-foot-long appendages that looked like they could easily disembowel a hungry raptor or even a good-sized tyrannosaur. Not only are these the longest claws of any dinosaur (or reptile) yet identified, but they're the longest claws of any animal in the history of life on earth—even exceeding the gigantic digits of the closely related Deinocheirus, the "terrible hand."

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Therizinosaurus Used its Claws to Collect Vegetation

Therizinosaurus claw
Walter Geiersperger / Getty Images

To a layperson, the giant claws of Therizinosaurus signify only one thing—a habit of hunting and killing other dinosaurs, in as grisly a manner as possible. To a paleontologist, however, long claws connote a plant-eating lifestyle; Therizinosaurus clearly used its extended digits to rope in dangling leaves and ferns, which it then voraciously stuffed into its comically small head. (Of course, these claws may also have come in handy for intimidating predators like the eternally hungry Alioramus.)

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Therizinosaurus May Have Weighed as Much as Five Tons

Modle of Therizinosaurus outside with two children posing by hands

Mystic Country CT/Flickr/CC BY-ND 2.0 

Just how big was Therizinosaurus? It was hard to reach any conclusive size estimates just on the basis of its claws, but additional fossil discoveries in the 1970s helped paleontologists to reconstruct this dinosaur as a 33-foot-long, five-ton, bipedal behemoth. As such, Therizinosaurus is the largest identified therizinosaur, and it weighed only a few tons less than the roughly contemporary Tyrannosaurus Rex of North America (which pursued a completely different lifestyle).

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Therizinosaurus Lived During the Late Cretaceous Period

Alioramus dinosaur walking in a stream.
Alioramus. Elena Duvernay/Stocktrek Images / Getty Images

Mongolia's Nemegt Formation provides a valuable snapshot of life during the late Cretaceous period, about 70 million years ago. Therizinosaurus shared its territory with dozens of other dinosaurs, including "dino-birds" like Avimimus and Conchoraptor, tyrannosaurs like Alioramus, and giant titanosaurs like Nemegtosaurus. (At that time, the Gobi Desert wasn't quite as parched as it is today, and was able to support a sizable reptilian population).

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Therizinosaurus May (or May Not) Have Been Covered in Feathers

Fully feathered drawing of Therizinosaurus

Mariolanzas/Wikimedia Commons/CC BY-SA 4.0 

Unlike the case with some other Mongolian dinosaurs, we have no direct fossil evidence that Therizinosaurus was covered in feathers—but given its lifestyle, and its place in the theropod family tree, it likely had feathers during at least some part of its life cycle. Today, modern depictions of Therizinosaurus are split between fully feathered recreations (which look a bit like Big Bird on steroids) and more conservative reconstructions in which the "reaping lizard" has classic reptilian skin.

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Therizinosaurus Has Lent Its Name to an Entire Family of Dinosaurs

A grouo of Scelidosaurus, Nothronychus and Argentinosaurus dinosarus grazing on trees and leaves.
A Nothronychus eating leaves from the apple tree. Mohamad Haghani / Getty Images

Somewhat confusingly, Therizinosaurus has eclipsed Segnosaurus as the eponymous dinosaur of its "clade," or family of related genera. (What were once known as "segnosaurs," a few decades ago, are now referred to as "therizinosaurs.") For a long time, therizinosaurs were thought to be restricted to late Cretaceous eastern Asia, until the discovery of the North American Nothronychus and Falcarius; even today, the family still consists of only two dozen or so named genera.

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Therizinosaurus Shared Its Territory with Deinocheirus

Deinocheirus dinosaur in an enviornment of ponds and calamites.
Elena Duvernay/Stocktrek Images / Getty Images

To show how difficult it can be to classify animals from the distance of 70 million years, the dinosaur to which Therizinosaurus bears the most resemblance wasn't technically a therizinosaur, but an ornithomimid, or "bird mimic." The central Asian Deinocheirus was also endowed with huge, fierce-looking claws (hence its name, Greek for "terrible hand"), and it was in the same weight class as Therizinosaurus. It's unknown if these two dinosaurs ever battled each other on the Mongolian plains, but if so, it must have made for quite a show.

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Strauss, Bob. "10 Facts About Therizinosaurus, the Reaping Lizard." ThoughtCo, Feb. 16, 2021, thoughtco.com/things-to-know-therizinosaurus-the-reaping-lizard-1093801. Strauss, Bob. (2021, February 16). 10 Facts About Therizinosaurus, the Reaping Lizard. Retrieved from https://www.thoughtco.com/things-to-know-therizinosaurus-the-reaping-lizard-1093801 Strauss, Bob. "10 Facts About Therizinosaurus, the Reaping Lizard." ThoughtCo. https://www.thoughtco.com/things-to-know-therizinosaurus-the-reaping-lizard-1093801 (accessed May 29, 2023).