Nothronychus

Phylogeny: Dinosauria > Saurischia > Theropoda > Neotheropoda > Tetanurae > Avetheropoda > Coelurosauria > Maniraptora > Therizinosauria > Therizinosauroidea > Therizinosauridae

Overview: Nothronychus, like most therizinosaurs, was a very bizarre theropod. Unlike most other theropods, or dinosaurs in general, it didn’t hold its torso fully horizontally, but semi-upright, giving it a taller profile in addition to its elongated neck. The skull was small and narrow, sporting a beak at the front of its mouth and teeth farther back along the jaws. Nothronychus, like most of its kin, possessed proportionately large and powerful arms, the hands of which sported three long, sickle-shaped claws. Other oddities included its ornithischian-like pelvis, despite being a saurischian, and its enlarged first toe, or dewclaw. Said dewclaw was adapted for bearing its weight, unlike on most other theropods where it was held off the ground and heavily reduced in size. Nothronychus was a herbivore, similar to most other therizinosaurs, though they all evolved from an earlier carnivorous ancestor, possibly in the Jurassic Period. The enlarged claws on its hands were likely used both for pulling down and manipulating branches, as well as physical defense against predators.

Fossils belonging to Nothronychus were first described in 2001, having been found within the rocks of New Mexico’s Moreno Hill Formation. The genus’s name means “slothful claw”, inspired by its sloth-like claws and the general similarities between therizinosaurs and extinct ground sloths. Two species of Nothronychus are known – Nothronychus mckinleyi and Nothronychus graffami. Fossils of the second species, described in 2009, come from Utah’s Tropic Shale Formation, which dates to a few million years before the type species. Putting the known fossils of both species together, the majority of the skeleton is known for this genus, minus the skull and a few other bones. We know it was a derived therizinosaur, belonging to the family Therizinosauridae, making it closely related to dinosaurs like Segnosaurus, Neimongosaurus, and Therizinosaurus itself. Nothronychus was smaller than Therizinosaurus, being a medium-sized therizinosaur of four to five meters long. This genus probably coexisted with other Moreno Hill dinosaurs like Suskityrannus and Zuniceratops.