Nothronychus
Nothronychus Temporal range: Late Cretaceous, [1]
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Reconstructed skeleton of N. mckinleyi | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Clade: | Dinosauria |
Clade: | Saurischia |
Clade: | Theropoda |
Superfamily: | † Therizinosauroidea
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Family: | †Therizinosauridae |
Genus: | †Nothronychus Kirkland & Wolfe, 2001
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Type species | |
†Nothronychus mckinleyi Kirkland & Wolfe, 2001
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Other species | |
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Nothronychus (meaning "slothful claw") is a
Nothronychus were bulky
History of discovery
The first fossil evidence later attributed to Nothronychus was discovered by a team of paleontologists working in the Zuni Basin of
A second, more complete specimen, UMNH VP 16420, was discovered from the
The Utah specimen studied by the MNA team was found to be closely related to N. mckinleyi, though it differed in build (being heavier) and age (about half a million years older).[3] The MNA specimen was first announced in two 2002 talks during the 54th meeting of the Rocky Mountain Geological Society of America.[6][7] It was later discussed in an issue of Arizona Geology as a distinct species from N. mckinleyi, but not named.[3] The specimen was classified and named as the new species Nothronychus graffami by Lindsay Zanno and colleagues in the journal Proceedings of the Royal Society B on 15 July 2009. N. graffami was named for Graffam, who discovered the original specimens.[4] A reconstructed skeleton of N. graffami went on display at the MNA in September 2007.[3] In 2015, Hedrick and colleagues conducted a large osteological revision of both species and their respective specimens concluding that Nothronychus was one of the most complete and well-known therizinosaurids.[8]
Description
Nothronychus is a medium-sized therizinosaur, measuring 4.2–5.3 m (14–17 ft) long and weighing 800–1,200 kg (1,800–2,600 lb).
The genus Nothronychus can be distinguished from other therizinosaur taxa based on several features: a distinctly subcircular obturator process, an elongated obturator foramen towards the bottom, the contact area between pubis and ischium restricted to the upper half of the obturator projection, and deep cut between towards the bottom facet of the obturator process and frontal ischial shaft.[8]
Both species, N. mckinleyi and N. graffami, are known from mature specimens of similar size, as evidenced by the fusion of the neural spines and scapulocoracoid.
Classification
Nothronychus were members of the
Therizinosauridae |
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Paleobiology
Feeding
In 2009, Zanno and colleagues stated therizinosaurs were the most-widely regarded candidates for herbivory among theropods based on the small, densely packed, coarse serrations; lance-shaped teeth with a relatively low replacement rate; a well-developed keratinous beak; long neck for browsing; relatively small skulls; a very large gut capacity as indicated by the rib circumference at the trunk and the outwards flaring processes of the ilia; and the notable lack of cursorial adaptations in the hind limbs. All of these features suggest that members of this family feed on vegetation, as well as pre-processing it within their mouths to begin the breakdown of cellulose and lignin. This is perhaps even more so true for therizinosaurids, which seem to have further exploited these characters. One of the most notable adaptations in advanced therizinosaurids are the four-toed feet, which had a fully functional, weight-bearing first digit that was likely adapted to slow life-style. Zanno and colleagues found that Ornithomimosauria, Therizinosauria, and Oviraptorosauria had either direct or morphological evidence for herbivory, which would mean either this diet evolved independently multiple times in coelurosaurian theropods or that the primitive condition of the group was at least facultative herbivory with carnivory only emerging in more derived maniraptorans.[4]
In 2014, Lautenschlager tested the
Myology
In 2015, Smith studied the myology and functional morphology of the craniocervical junction of N. mckinleyi. The craniocervical muscles can be subdivided into functional groups as dorsiflexors, lateroflexors, and ventroflexors. Lateroflexors and dorsiflexors in Nothronychus are relatively reduced but are still well-developed, while ventroflexors allow increased ventroflexion. With small neural spines relative to the long S-shaped neck, its neck pattern was similar to that of ostriches and Diplodocus. Its individual centra didn't have high degree of freedom and likely had little apparent movement, meaning that the total neck movement would have only been resulted by the combined effect of all cervical vertebrae.[14]
In 2021, he also reconstructed the forelimb musculature of both species in the same year. As predicted for derived non-avian theropod dinosaurs, the forelimbs likely had no increase in range of motion within them. The distal humerus contained a well-developed fossa brachialis, and the proximal humerus may have had a fossa pneumotricipitales; the deflected epicleidium of the furcula is a development yet to be described in other theropods. Other forelimb musculature were similar to
In the same year, Smith reconstructed the hindlimb musculature of N. graffami. Nothronychus had a pelvis that is incipiently opisthopubic, which Smith expects to be associated with the muscular system's extensive modification. His reconstruction of the muscular system revealed that the musculature of Nothronychus to a certain extent is convergent with birds because of the retroverted pubis that becomes fused with the ischium, and because of the synsacrum and pes similar to that of birds. It also showed that its musculature was not only convergent with birds, but also with ornithischians, indicating that some maniraptorans' retroverted pubis and the ornithischians' postacetabular bar are analogous structures.[16] A 2023 study by Smith and Gillette suggests that much of the walking motion for N. graffami took place at the knee when moving, with movement at the femur limited. This same study also suggests a waddling gait for Nothronychus, and a digitigrade stance, though plantigrade walking could not entirely be ruled out.[17]
Senses and breathing
In 2012, paleontologist Stephan Lautenschlager and team examined the endocasts (brain cavity) of several therizinosaurs (including N. mckinleyi), concluding that most members had well developed senses of smell, hearing, and balance, mostly useful for foraging. The enlarged forebrain of therizinosaurs may also have been useful in complex social behavior and predator evasion. These senses were also well-developed in earlier coelurosaurs and other theropods, indicating that therizinosaurs may have inherited many of these traits from their carnivorous ancestors and used them for their different and specialized dietary purposes.[18]
In 2018, the holotype braincase of Nothronychus mckinleyi was re-examined by Smith and colleagues updating numerous basicranial and soft-tissues aspects. They noted that the braincase has particularly large
In 2021, Smith and colleagues examined the pneumaticity of both species' specimens. The axial skeleton ("the basicranium, the presacral vertebrae, and the proximal caudal vertebrae") shows extensive pneumatization, meaning that this body part of Nothronychus had extensive air sacs. The synsacrum and ilium is not pneumatized, so the air sac may have bypassed the synsacrum. The researchers considered that the pneumatization in therizinosaurs wouldn't have been related to weight reduction or thermoregulation, but to an avian-style respiratory system. With lungs attached to the dorsal vertebrae, Nothronychus might have had a respiratory system similar to that of birds, probably having an "avian-style unidirectional airflow with cross-current blood/oxygen exchange." Unlike birds, however, the clavicular air sac of Nothronychus might have been reduced or just absent, evidenced by the lack of pneumatic furcula or appendicular elements. Its ribs also show no sign of uncinate processes.[20]
Paleoenvironment
Specimens of Nothronychus are known from the
See also
References
- ^ PMID 33854833.
- ^ S2CID 85705529.
- ^ a b c d Gillete, D. D. (2007). "Therizinosaur—Mystery of the Sickle-Claw Dinosaur" (PDF). Arizona Geology. 37 (2): 1−6.
- ^ PMID 19605396.
- ^ S2CID 53405097.
- ^ Albright, L. B.; Gillete, D. D.; Titus, A. L. (2002). "New records of vertebrates from the Late Cretaceous Tropic Shale of Southern Utah". Paleontological Research in Grand-Staircase Escalante National Monument and Surrounding Area I. Archived from the original on 2011-06-08.
- ^ Gillete, D. D.; Albright, L. B.; Titus, A. L.; Graffam, M. H. (2002). "Discovery and excavation of a therizinosaurid dinosaur from the Upper Cretaceous Tropic Shale (Early Turnoian), Kane County, Utah". Paleontological Research in Grand-Staircase Escalante National Monument and Surrounding Area I. Archived from the original on 2011-06-08.
- ^ PMID 26061728.
- ISBN 9780691167664.
- ^ .
- PMID 31333906.
- PMID 24807260.
- PMID 25706764.
- PMID 33665832.
- S2CID 231195324.
- S2CID 257583565.
- PMID 23284972.
- PMID 30063717.
- PMID 33044012. Text was copied from this source, which is available under a Creative Commons Attribution 4.0 International License.
- PMID 31061476.
- ^ S2CID 253905727.
- ^ Wolfe, D.G; Kirkland, J.I. (1998). "Zuniceratops christopheri n. gen. & n. sp., a ceratopsian dinosaur from the Moreno Hill Formation (Cretaceous, Turonian) of west-central New Mexico". New Mexico Museum of Natural History and Science, Bulletin. 14: 303–317.