The Killer Claws That Deceived us All: Therizinosaurus

The natural world is full of oddities. From the largest creatures to the smallest microbes, the Earth is full of extraordinary animals, people and things. This principle was no different during the time of the dinosaurs, when the world was populated with weird and wonderful creatures. In a series of articles, I will share my top picks for the most peculiar dinosaurs known to science and talk about what exactly made them so odd….

Dinosaurs don’t typically have big claws. Take for instance the puny arms of carnivores like the Tyrannosaurids or Abelisaurids, so diminutive that they would have been largely useless for these animals. With this in mind, you can imagine the shock of paleontologists in the 1950’s upon discovering a set of claws that were over a meter long. In fact, the initial discovery of these behemoth claws was met with such confusion that they were not considered dinosaur bones. Instead, the claws were perceived to have belonged to a massive turtle, perhaps using these claws as a means to dig up sediments on ancient rivers or seas. While this initial assessment would soon prove to be inaccurate, one key element would carry over in subsequent descriptions: its name, Therizinosaurus.

Close Relatives Reveal Its True Appearance

It would take another two decades until paleontologists realized Therizinosaurus was not a turtle. Starting in the 1970’s, additional remains of the original Therizinosaurus specimen were revealed, allowing paleontologists to properly describe Therizinosaurus as a dinosaur. While realizing its lineage was certainly important, the remains only comprised arms and parts of the legs, thus giving an incomplete picture of the animals’ true appearance. The appearance was finally revealed with the discovery of close relatives, not by the actual Therizinosaurus fossils. The finds of multiple new relatives finally gave paleontologists a clear image of what Therizinosaurus looked like. In fact, if it weren’t for the discoveries of its close relatives, there would be very little known about these peculiar dinosaurs.

The Oddities of The Dinosaur Kingdom

In contrast to the horizontal posture of most dinosaur species, the Therizinosaurids stood almost upright due to flexible hips. These hips were also built to support a fair amount of weight from its gut. The legs and tails of most Therizinosaurids are short compared to other dinosaurs, indicating that they were not built for running. Their neck was long and flexible, with a proportionately tiny head. To top it off, their skull contained a number of teeth with a beak at the end of their snout. The unique appearance of Therizinosaurus and its kin are part of what makes them such a fascinating lineage.

 A Diet Rich in Fibre

Therizinosaurus was part of the Theropods, the branch of dinosaurs that contains all carnivorous species. In fact, Therizinosaurus was a relatively close cousin of Tyrannosaurus! It is because of this ancestry that the diet of Therizinosaurus is so peculiar. As noted, the skulls of Therizinosaurids are small and delicate, with teeth suited to cutting through vegetation, not flesh. It would seem that the Therizinosaurids became herbivorous, allowing them to feast on a wider range of sources than its Tyrannosaurid cousins. It is also apparent this diet may have helped fuel their success; they were found across both Asia and North America, thrived for some 80 million years and went extinct just before the asteroid struck that finished off the other non-avian dinosaurs for good.

Shaggy Giants

Like other theropods, Therizinosaurus would have been covered in layers of feathers. In 1999, an early Therizinosaurid named Beipiaosaurus was discovered in China that sported a heavy coating of feathers on its body. Since Beipiaosaurus was an early member of the family and lived some 50 million years prior to Therizinosaurus, it is likely that feathers were a basal trait of the family and were present on all members. Like other theropods, these feathers would have been used for both for display (to attract potential mates) and insulation, keeping these dinosaurs warm throughout the year.

Multi-Use Talons

What were those massive claws used for? While paleontologists can never be quite sure, they have come up with a few intriguing theories for their function. One proposed use for the claws was as a defense mechanism. In the late cretaceous of Mongolia, Therizinosaurus would have lived a dangerous life. Three separate species of Tyrannosaurids would have shared its habitat, with all viewing Therizinosaurus as a potential meal. The massive claws certainly would have been able to repel attackers; whether it repelled them through intimidation or outright attack is up for debate. In addition to defense, the claws also would have been used for foraging food. Like modern sloths, Therizinosaurids may have used their claws to grasp branches and bring their food down to them. Lastly, they may have been used to dig for roots and other ground level plants, enabling them to have a larger variety in their diet. It’s clear that the claws of Therizinosaurus had a wide arrange of uses, acting like a swiss army knife for these magnificent dinosaurs. 

When I first learned about Therizinosaurus, I was mesmerized. How could an animal with the perfect tools for killing really be just a mundane herbivore? With its “alien” body and strange behaviours, it is almost incomparable to any other animal, living or extinct. Out of all the bizarre dinosaurs I have covered on this website, Therizinosaurus is by far the strangest dinosaur yet.

As I continue my Bizarre Dinosaurs series, it will be difficult to find a challenger to the absurdity that is Therizinosaurus.

References:

I do not take credit for any artwork in this article.

Therizinosaurus courtesy of the fantastic book All Yesterdays:

Conway, John, et al. All Yesterdays: Unique and Speculative Views of Dinosaurs and Other Prehistoric Animals. Irregular Books, 2013. https://www.tor.com/2013/01/04/book-review-all-yesterdays-daren-naish-john-conway-cm-koseman-scott-hartman/

Erlikosaurus art courtesy of Scott Reid, found here: https://adinosauraday.wordpress.com/2019/10/10/erlikosaurus-andrewsi/

Image for the claws found Here

Image for Arms found Here

Choi, Charles Q. “My, What Big Claws! Dino Talons Used for Digging.” LiveScience, Purch, 6 May 2014, www.livescience.com/45401-dinosaur-claws-used-for-digging.html.

“Comparing Species.” Dinosaur Facts and Figures: the Theropods and Other Dinosauriformes, by Molina-Pérez Rubén et al., Princeton University Press, 2019, pp. 52–53.

Langley, Liz. “Which Animal Has the Longest Claws of All Time?” National Geographic, 9 Aug. 2017, www.nationalgeographic.com/news/2015/12/151226-animals-dinosaurs-claws-ancient-science-paleontology/.

“Prey.” The Tyrannosaur Chronicles: the Biology of the Tyrant Dinosaurs, by David W. E. Hone and Scott Hartman, Bloomsbury Sigma, an Imprint of Bloomsbury Publishing Plc, 2017, pp. 192–194.

Xu, Xing, et al. “A New Feather Type in a Nonavian Theropod and the Early Evolution of Feathers.” PNAS, National Academy of Sciences, 20 Jan. 2009, www.pnas.org/content/106/3/832.