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Nothronychus

Kirkland & Wolfe, 2001 noh-THRON-i-kus

From Greek 'nothros' meaning 'slothful' and 'onyx' meaning 'claw'; translates as 'slothful claw', a reference to its therizinosaur-like elongated claws and presumed slow-moving herbivorous habits.

93.9–89.8 million years ago Turonian, Late Cretaceous
Late Cretaceous stages

Nothronychus 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 Turonian stage of the Late Cretaceous. A second specimen, described in 2009 as a second species, Nothronychus graffami, was found in the Tropic Shale of Utah; Hedrick and colleagues (2015) estimate it to be at least 1.5 and up to 3 million years older than N. mckinleyi.

Diagnosis

  1. Distinctly subcircular obturator process of the ischium.
  2. Ovoid, dorsoventrally elongate obturator foramen, its maximum length more than 200% of its maximum width.
  3. Contact between the pubis and ischium restricted to the proximal half of the obturator process.
  4. Deep notch between the ventral aspect of the obturator process and the cranial ischial shaft.
  5. In the type species N. mckinleyi, the ventral notch between the obturator process and the iliac shaft is craniocaudally narrow (wide in N. graffami), the cranial caudal centra are platycoelous, and the caudal centra bear a hypertrophied caudoventral heel about one-third the centrum length.
  6. In N. mckinleyi, the glenoid lacks a caudal buttress and the caudal process of the ischium is poorly defined and elongate, extending to the shaft opposite the obturator process.

Species (2)

Nothronychus mckinleyi Kirkland & Wolfe, 2001

Type species

Named for rancher Bobby McKinley, on whose land the fossil findings were made.

Holotype
MSM P2117 , Arizona Museum of Natural History (formerly Mesa Southwest Museum)
Material
Partially disarticulated skeleton: isolated teeth, a partial braincase and cranial fragments, fragments of seven cervical vertebrae, one cranial dorsal vertebra, a dorsal centrum, one mid-caudal vertebra, cervical and dorsal ribs, fused gastralia, a chevron fragment, the left scapula, right humerus and ulna, a distal metacarpal II and two manual phalanges, both ischia, both tibiae, the right fibula, a partial metatarsal II, three pedal phalanges, and two pedal unguals.
Horizon
lower Moreno Hill Formation, Turonian, Late Cretaceous , 93.9–89.8 million years ago
Locality
Haystack Butte, New Mexico, United States

Nothronychus graffami Zanno et al., 2009

Honors M. Graffam, who discovered the holotype.

Holotype
UMNH VP 16420 , Utah Museum of Natural History
Material
Nearly complete postcranial skeleton, including cervical, dorsal, sacral and caudal vertebrae, pectoral girdle, forelimbs, pelvis, hindlimbs and pes; skull not preserved
Horizon
Tropic Shale Formation, Turonian, Late Cretaceous , 93.9–89.8 million years ago
Locality
Utah, United States
Diagnosis
  1. Cranial caudal vertebral centra strongly amphicoelous (platycoelous in N. mckinleyi)
  2. Caudoventral aspect of the caudal centra poorly developed (hypertrophied heel about one-third the centrum depth in N. mckinleyi)
  3. Glenoid with a pronounced caudal buttress (absent in N. mckinleyi)
  4. Ventral notch between the obturator process and iliac shaft craniocaudally wide (narrow in N. mckinleyi)
  5. Pubic boot with a diminutive caudal process bearing a dorsally convex ventral margin
  6. Subtriangular caudal process of the ischium diminutive (less than 5% of ischium length), located proximal to the obturator foramen

References

  1. Kirkland, J. I.; Wolfe, D. G. (2001). First definitive therizinosaurid (Dinosauria; Theropoda) from North America. Journal of Vertebrate Paleontology 21(3): 410-414. Informa UK Limited. doi:10.1671/0272-4634(2001)021[0410:fdtdtf]2.0.co;2 kirkland2001a
  2. Hedrick, B. P.; Zanno, L. E.; Wolfe, D. G.; Dodson, P. (2015). The Slothful Claw: osteology and taphonomy of Nothronychus mckinleyi and N. graffami (Dinosauria: Theropoda) and anatomical considerations for derived therizinosaurids. PLOS ONE 10(6): e0129449. Public Library of Science (PLoS). doi:10.1371/journal.pone.0129449

    Osteological redescription of both Nothronychus species; corrects characters interpreted as diagenetic artifacts and follows Zanno's amended diagnoses.

    hedrick2015a
  3. Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Theropods. Princeton University Press.

    Source of the hip height estimate, and the appearance features.

    jones2026c
  4. Zanno, L. E.; Gillette, D. D.; Albright, L. B.; Titus, A. L. (2009). A new North American therizinosaurid and the role of herbivory in 'predatory' dinosaur evolution. Proceedings of the Royal Society B: Biological Sciences 276(1672): 3505-3511. The Royal Society. doi:10.1098/rspb.2009.1029 zanno2009a