Describer

Kirkland & Wolfe, 2001

Time

Cretaceous Late Turonian

Classification

Saurischia Theropoda Tetanurae Coelurosauria Therizinosauroidea Therizinosauridae

Diet

?

Fossilsite

Moreno Hill Formation Haystack Butte Locality of the southern Zuni Basin, Catron County of west-central, New Mexico, US

Length

4.5 - 6 meter

Info

Nothronychus mckinleyi (Kirkland & Wolfe, 2001) > Nothronychus graffami (Zanno, Gillette, Albright & Titus 2009)

Genus - Typespecies

(Sloth-like claw) Nothronychus was larger than Erlikosaurus or Segnosaurus but in some ways more primitive than his Asian relatives. Nothronychus is closer to these than Beipiaosaurus and Alxasaurus. Nothronychus had a long thin neck long arms, dexterous hands, four-inch curved claws on its fingers, a large abdomen, a small head with a mouth full of leaf-shaped teeth designed for shredding vegetation, a relatively short tail and stout back legs. [Holotype is MSM P-2117]

Nothronychus is significant and derived from other therizinosaurs (segnosaurs) by the presence of posterior serrations (ant:post serration ratio is 10:13 per 5mm) that progress proximally on the crown to the limit of the \\\"neck\\\" constriction. The dorsal pneumatic fossa is enclosed withing a depression bearing numerus foramina; there is no posteromedial crest on the humerus, referred to as a \\\"spur\\\" by the authors; the claws do not have distinct flexor tubercles or flexor lips, unlike more advanced therizinosauroids or Beipiaosaurus; the obturator process of the ischium is large and sub-circular/-rectangular, the body of the ischium is very thin, with virtually no acetabular margin; the anterior process for the M. iliofibularis is located near the midshaft of the fibula. Also, the mid- to post-cervicals are extensively invaginated by several foramina ventral to the diapophysis, and the pedal unguals have a lateral twist to the claw, making the ventral surface face laterally.

The teeth are curved medially, and have a strong caudal curvature, unlike all other segnosaurs, including Beipiaosaurus. Cervicals are platycoelous to amphicoelous, like other therizinosauroids but not either species of Nanshiungosaurus, and the neural spine shape is distinctively rectangular and thin, rather than broad and distally tapering, as in Nanshiungosaurus and Alxasaurus; the cervicals of Segnosaurus remain unfigured and un-comparable. The anterior cervical has a hyposphene, so it is presumable that hyposphene--hypantra progress through the anterior dorsals, they are lacking in cervicals. The authors suggest that Chilantaisaurus zheziangensis may be referrable to Nanshiungosaurus.

Kirkland and Wolfe discuss slightly the jaw of Eshanosaurus, remarking on the presence of a medial ridge on the crowns as in prosauropods. They suggest a phylogenetic analysis is in preparatio by the authors, but so far the animal is referred to as a therizinosaurid, more advanced than Alxasaurus, but as the most basal therizinosaurid.

The names of this genus and species of therizinosauroid first appeared in Arizona Republic for June 19, 2001 (R. E. Molnar, pers. comm.). They were subsequently (August 22, 2001) formally described in Journal of Vertebrate Paleontology 21(3).

Thanks to Jaime A. Headden

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