Therizinosaurus lived during the Late Cretaceous period, approximately 70 million years ago, in what is now Mongolia. First discovered in 1948, its initial fossil remains were so unusual that scientists misidentified them, even suggesting they might belong to a giant marine turtle. Its unique anatomy has made it a subject of scientific interest.
Overall Body Dimensions
Therizinosaurus cheloniformis was a large, two-legged dinosaur. It is estimated to have reached lengths of 9 to 10 meters (30 to 33 feet) from head to tail and stood 4 to 5 meters (13 to 16 feet) tall. To visualize this, a Therizinosaurus would be roughly the length of a school bus.
Mass estimates range from over 5 metric tons (5.5 short tons) to as much as 10 metric tons (11 short tons), comparable to a large African elephant. These dimensions position Therizinosaurus as one of the largest theropods and the largest known member of its group, the therizinosaurs. Its robust body likely supported a slow-moving, high-browsing lifestyle.
The Remarkable Claws
The most striking feature of Therizinosaurus was its exceptionally long claws, which give the dinosaur its name, meaning “scythe lizard.” These claw bones are considered the longest known from any land animal. Each of its three-fingered hands bore these claws, which could reach lengths exceeding 50 centimeters (20 inches). Some estimates suggest they could extend up to 91 centimeters (3 feet) along their outer curve.
Unlike the strongly curved claws of many other theropods, Therizinosaurus’s claws were relatively straight, only curving significantly at their tips. Their primary purpose was likely for gathering vegetation, such as pulling down branches, rather than for hunting. These enormous appendages also served as a potential deterrent against large predators.
Estimating Ancient Sizes
Paleontologists estimate the size of extinct animals like Therizinosaurus using various scientific methodologies, often relying on incomplete fossil records. Therizinosaurus is known from fragmented remains, including arm, leg, and rib bones, making full body reconstructions a process of careful inference.
One common approach involves comparative anatomy, where scientists scale up from more complete skeletons of related species. By examining the proportions of known bones, they can extrapolate the likely size of missing parts.
Another method involves analyzing the dimensions of limb bones, particularly their circumference. The thickness of weight-bearing bones like the femur and humerus can provide an indication of animal’s overall mass. While these methods provide robust estimates, the inherent challenges of working with fossils mean that size ranges are often presented, reflecting scientific uncertainty and ongoing research in paleontology.