Nothronychus

Nothronychus is a genus of dinosaur classified in the group Therizinosauria, strange theropods with a toothless beak, a bird-like hip (resembling the non-related ornithischians) and four-toed feet, with all four toes facing forward. The type species of this dinosaur was found by Kirkland and Douglas G. Wolfe in 2001 near New Mexico's border with Arizona, in an area known as the Zuni Basin.

The name Nothronychus, derived from Greek meaning 'sloth-like claw', was selected because the animal reminded Kirkland of a giant ground sloth. It is the first example of therizinosaurs to be found in the Americas. Previous discoveries had been from China and Mongolia. Nothronychus was larger than Erlikosaurus or Segnosaurus but in some ways more primitive than these Asian relatives. A related dinosaur from a significantly earlier period, Falcarius utahensis, was discovered in Utah in 2005.

The sloth-like Nothronychus lived 90 million years ago, during the Late Cretaceous Period of the Mesozoic era, in swampy forests similar to modern bayous in Louisiana. The era was a period of extreme global warming, with ocean levels 300 m (1,000 ft) higher than current levels and a significantly reduced amount of dry land. Almost no dinosaur fossils have been found from this time, particularly in North America, making this and associated discoveries very important.

Nothronychus is a member of the theropod group of carnivorous dinosaurs that includes Tyrannosaurus but Nothronychus, and its close relatives, evolved into plant-eaters. It was bipedal and walked more upright than its carnivore ancestors. The creature weighed about a tonne, was 4.5-6 m (15-20 ft) long and stood 3-3.6 m (10-12 ft) tall.

A reconstruction of 40 to 50 percent of its skeleton, from two separate finds, allows scientists to describe the dinosaur as having:


 * a small head with a mouth full of leaf-shaped teeth, adapted for shredding vegetation,
 * a long, thin neck,
 * long arms with dexterous hands and 10 cm (4 in) curved claws on its fingers,
 * a large abdomen,
 * stout back legs and
 * a relatively short tail.

Bird-like characteristics and preserved feathers in fossils of its Asian relatives indicate Nothronychus may have had a downy coat of feathers, perhaps resembling an emu. No feather impressions were found with the fossil remains, probably because the surrounding sediment was unable to preserve such delicate features.

The Arizona Republic newspaper first announced the discovery on 19 June 2001 and the dinosaur's name, in a column by R. E. Molnar. Nothronychus was formally described in the Journal of Vertebrate Paleontology on 22 August 2001.