Mad about Science: Therizinosaurus

By Brenden Bobby
Reader Columnist

Dinosaurs were weird. Conditions on Earth over several hundreds of millions of years created some unusual evolutionary niches that nature was eager to fill.

The Therizinosaurus was one of these strange creatures filling a particular evolutionary niche during the late-Cretaceous period and among the last dinosaurs to walk the Earth before an asteroid wiped most of them from existence.

The strangeness of the Therizinosaurus  (the “reaping” or “scythe” lizard), is compounded by the massive knowledge gaps we have of the creature. We aren’t entirely sure if it was feathered or scaled or a mix of the two. We don’t have a full comprehension of exactly what it looked like, as we have only collected a handful of fossils and still don’t have a complete skeleton, but paleontologists have referenced the remains against similar species to piece together a rough understanding of what the creature may have looked like.

The Therizinosaurus was a therapod, which contained members such as the Tyrannosaurus rex, Carnotaurus, Archaeopteryx and even ostriches and ducks. It was believed to be a beaked herbivore that found its home in an area that would eventually become the Gobi Desert in Mongolia, where its fossils were extracted. One of the most peculiar features of the Therizinosaurus are the three scythe-like claws on its hands somewhat reminiscent of the Utahraptor’s toe claws. Unlike the Utahraptor, Therizinosaurus’ claws could stretch up to three feet and were believed to be used for snagging and shearing leaves from hard-to-reach places, as well as potentially warding off predators. It’s likely that Therizinosaurus used its long and imposing claws in similar ways to sloths.

Therizinosaurus had very large forearms, but relatively short and stocky rear legs that were believed to bear the bulk of the creature’s 5.5-ton weight. Proportionally, this creature likely looked completely ridiculous by animal standards of today. Given its strange frame, it’s likely the creature didn’t move very quickly but could deliver a devastating blow to potential predators if forced to do so. This thing was essentially the size of a small school bus with just as much weight at its disposal, ready to bear through six scythe-bladed claws.

The unusual crane-like frame of this dinosaur was believed to serve a specific evolutionary purpose that is strikingly similar to gorillas today. Despite having very stubby legs, it had a robust pelvis that seemed most suited for sitting. This likely means that the creature would meander to stationary food sources and sit down to pivot its long neck upward while it used its arms to pull down foliage to eat. Gorillas exhibit this sitting behavior while sloths exercise the pulling-food-to-mouth-with-claws behavior.

If feathered, this dinosaur very likely looked like a body-builder version of Big Bird, with a long neck, stout beak and a massive pot belly. A scaled version would have looked much stranger, at least to a human eye. Feathers provide ample insulation for animals to protect them from both heat and cold by trapping air between interlocking ridges. This is one of the reasons that down comforters are so good at keeping us toasty and warm in the winter: by trapping our body heat beneath the covers and not letting it radiate out into the open air.

The process of fossil discovery and categorization is always tricky business, especially when only partial fossils are recovered. Many dinosaurs have undergone critical changes in how we perceive them today. A great example of this is how the T. rex was depicted early on, as compared to today. Early discoveries of the Tyrannosaurus rex led paleontologists of the day to believe the creature stood upright with its tail low to the ground — this is famously depicted in Walt Disney’s 1940 masterpiece Fantasia during the “Rite of Spring” segment. Now it is generally understood that the T. rex stood horizontally, with its tail stretching out for balance similar to a crocodile.

This also occurred during the Therizinosaurus’ discovery and analysis. When it was discovered by a joint Soviet-Mongolian expedition in 1948, Russian scientist Evgeny Maleev believed that the Therizinosaurus was a massive turtle. It was identified as a member of the theropods in the 1970s, and then classified as a segnosaurid in the 1990s. Segnosaurids are bizarre theropods with pot bellies, long arms and necks and a taste for vegetation, in stark contrast to animals like the Tyrannosaurus rex.

The climate in which the Therizinosaurus thrived was vastly different from the Gobi Desert of today. The Cretaceous lands that would eventually become Mongolia were much wetter and were prime real estate for a vast number of ancient killer reptiles to inhabit, including the Alioramus, a dinosaur that appears similar to a much smaller T. rex while potentially preying on Therizinosaurus.

Looking back at the skeletal form of what the internet lovingly refers to as the “tickle-chicken,” one can see roughly how birds would come to evolve into the forms we know today, as countless generations shrank down and shifted to turn pronged claws into wings for flight. A cooler world led to a scarcity of resources, which favored smaller and more agile feeders over the hulking behemoths that once stomped across the land.

Lucky for us — because not a single one of us would like to meet a six-ton dinosaur on the highway on a dark winter’s night.

Stay curious, 7B.