Prehistoric Animals


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With its imposing 3 feet long claws, its pot-belly, its supple and elongated neck and its screaming plumage, the Therizinosaurus (which means "scythe lizard" in Greek) is among the strangest dinosaurs to have existed. This 33 feet long bipedal behemoth weighted in the vicinity of 5 tons – only a few tons smaller than its contemporary Tyrannosaurus Rex – and lived in the Gobi Desert during the Upper Cretaceous period. Therefore, Therizinosaurus shared its territory with dozens of other dinosaurs including dino-birds like Avimimus and Velociraptor as well as some Asian tyrannosaurs and giant titanosaurs like Nemegtosaurus. At that time, the Gobi Desert was not desiccated as it is today and could withstand a considerable reptile population.

Before the Second World War, the Mongolian regions were accessible to almost any nations with the funding and desire to go there. After the Cold War began in 1948, a joint Russian-Mongolian expedition excavated the Therizinosaurus holotype specimen off the famous Nemegt Formation in the Gobi Desert.

A giant sea turtle

Perhaps due to the growing isolation of Russian scientists from Western countries, Yevgeny Maleev, the paleontologist in charge of the 1948 expedition, first identified the Therizinosaurus as a giant, 15-foot-long sea turtle equipped with huge claws. Maleev even went so far as to erect a new family, the Therizinosauridae, to accommodate what he then believed to be a unique branch of Mongolian sea turtles. As is often the case with fossil discoveries dating back to such a distant era, it can be very difficult to reconstruct the past and understand bones without having additional context. In doing so, it took more than 20 years for Therizinosaurus to finally be labeled in 1970 as a species of theropod dinosaur. It was only after we dug up the remains of close relatives like Segnosaurus and Erlikosaurus elsewhere in Asia that this dinosaur was identified as a segnosaurid, a bizarre family of theropods with long arms, pot-bellies and a preference for vegetation rather than flesh.

3 feet long claws, the hallmark of Therizinosaurus

Therizinosaurus claws
Therizinosaurus claws

The most striking feature of the Therizinosaurus is its curved sharp claws that seem easily able to disembowel a hungry raptor and perhaps even a good size tyrannosaurus. Not only are the claws of the Therizinosaurus the longest of all the dinosaurs ever identified but they are also the longest of all the animals in the history of life on Earth. They surpass even those of his close similar Deinocheirus, or "horrible hand".

For the profane and the bloodthirsty, such an arsenal can only mean one thing: the habit of hunting and killing other dinosaurs in the most frightful and macabre way one can imagine. For a paleontologist, however, such claws have a connotation that refers to an herbivore lifestyle. The Therizinosaurus clearly used his claws as humans use a rake to pick up the leaves and ferns that it then voraciously binged into his mouth. These claws could also have had a visual deterrent effect on nearby predators such as the Alioramus tyrannosaurus.

Therizinosaurus may have had feathers

Unlike other Mongolian dinosaurs such as Velociraptor, there is no direct fossil evidence that suggests Therizinosaurus was feathered; it is believed that, given its lifestyle and its place in the phylogenetic tree of theropods, this dinosaur probably had feathers at certain stages of his life. Nowadays, the Therizinosaurus is as much represented by paleoartists as having a large plumage as having a classic reptilian skin.

Therizinosaurus is the eponymous species of therizinosaurs

Skeleton fossil of Therizinosaurus
Skeleton fossil of Therizinosaurus

In a somewhat confusing way, the Therizinosaurus eclipsed the Segnosaurus to become the eponymous species of this kind. What was known as the segnosaurs a few decades ago is now referenced as the therizinosaurs. For a long time it was believed that therizinosaurs were restricted to the eastern Asian regions of the Late Cretaceous period until close relatives Nothronychus and Falcarius were discovered in North America. Even today, this dinosaur family has only about two dozen different genres.

In order to demonstrate how difficult it can be to classify 70 million-year-old animals, the dinosaur whose appearance is closest to that of the Therizinosaurus technically wasn’t even a therizinosaur, but rather an ornithomimid. The Central Asian Deinocheirus also sported enormous terrifying claws and was in the same weight class as the Therizinosaurus. A battle on the plains of Mongolia between these two dinosaurs would certainly be an unforgettable sight!

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