Nothronychus (meaning "slothful claw") is a genus of therizinosaurid theropod dinosaurs that lived in North America during the Late Cretaceous period. The type species, Nothronychus mckinleyi, was described by James Kirkland and Douglas G. Wolfe in 2001. It was recovered near New Mexico's border with Arizona, in an area known as the Zuni Basin, from rocks assigned to the Moreno Hill Formation, dating to the late Cretaceous period (mid-Turonian stage), around 92 million years ago. A second specimen, described in 2009 as a second species, Nothronychus graffami, was found in the Tropic Shale of Utah, dating to the early Turonian, between one million and a half million years older than N. mckinleyi.
Nothronychus were bulky herbivorous theropods with wide, sloth-like hip (resembling that of the non-related ornithischians), four-toed feet with all four toes facing forward, elongated necks and prominent arms with sharp claws. Both species were similar in dimensions, but N. graffami was slightly more robust than N. mckinleyi.
The first fossil evidence later attributed to Nothronychus was discovered by a team of paleontologists working in the Zuni Basin of New Mexico at the Haystack Butte site, Moreno Hill Formation. A therizinosaur ischium (a hip bone) had originally been mistaken for a squamosal, a part of the skull crest of the newly discovered ceratopsian Zuniceratops. However, closer examination revealed the true identity of the bone, and soon more parts of the skeleton were found. The New Mexico team, led by paleontologists Jim Kirkland and Doug Wolfe, published their find in the Journal of Vertebrate Paleontology on 22 August 2001, making it the type specimen of the new species Nothronychus mckinleyi. The Arizona Republic newspaper, however, was first to announce the name on 19 June 2001, in a column by R.E. Molnar. The generic name, Nothronychus, is derived from Greek νωθρός (, meaning slothful) and ὄνυξ (onyx, meaning claw). The specific name, mckinleyi, honours rancher Bobby McKinley on whose land the fossil findings were made.