Nothronychus is a genus of dinosaur classified in the group Therizinosauria, strange herbivorous 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, N. mckinleyi, was described by James Kirkland and Douglas G. Wolfe in 2001 near New Mexico's border with Arizona, in an area known as the Zuni Basin. It was recovered from rocks assigned to the Moreno Hill Formation, dating to the late Cretaceous period (mid-Turonian stage), around 91 million years ago. A second specimen, described in 2009 as a second species, N. graffami, was found in the Tropic Shale formation of Utah, dating to the early Turonian, between 1 million and a half million years before N. mckinleyi.
The name Nothronychus, derived from Greek meaning 'sloth-like claw', was selected because the animal reminded Kirkland of a giant ground sloth.
Discovery[]
Known elements from N. mckinleyi in blue, N. graffami in red and both species in purple
The first fossil evidence later attributed to Nothronychus was discovered by a team of paleontologists working in the Zuni Basin of New Mexico. A therizinosaur illium (hip bone) had originally been mistaken for a part of the 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, lead 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.[1] The Arizona Republic newspaper, however, was first to announce the name on 19 June 2001, in a column by R.E. Molnar. Nothronychus derives from the Greek νωθρός (nothros), "slothful" and ὄνυξ (onyx), "claw". "Mckinleyi" refers to Bobby McKinley, a rancher whose land brought the Nothronychus remains. MSM P2106, the holotype, consists of a partial skull, a braincase, several vertebrae, parts of the shoulder girdle, forelimbs, a pelvis and hindlimbs.
Localities where MSM P2106 and UMNH VP 16420 have been found
A second, more complete therizinosaur specimen was discovered from the Tropic Shale formation (dating to the early Turonian stage) of southern Utah in 1999 by Merle Graffam, a resident of Big Water, Arizona. The area around Big Water had been subject to several expeditions by teams from the Museum of Northern Arizona (MNA), and was known for its abundance of marine reptile fossils, especially plesiosaurs.[2] During part of the late Cretaceous period, the region had been submerged under a shallow sea, the Western Interior Seaway, and preserves extensive marine deposits. Graffam's initial discovery (a large, isolated toe bone) came as a surprise to scientists, as it clearly belonged to a land-dwelling dinosaur, rather than a plesiosaur. However, the location of the bone at the time would have been nearly 100 kilometers from the Cretaceous shoreline. An excavation of the area by an MNA crew revealed more of the skeleton, and the scientists found that it was a therizinosaur, and the first example of that group to be found in the Americas. N. graffami was erected, being the most complete, but lacking a skull. All previous therizinosaur fossils had come from China and Mongolia.[1]
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).[2] The MNA specimen was first announced in two 2002 talks during the 54th meeting of the Rcoky Mountain Geological Society of America.[3][4] It was later discussed in an issue of Arizona Geology as a distinct species from N. mckinleyi, but not named.[2] 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.[5] A reconstructed skeleton of N. graffami went on display at the MNA in September 2007.[2] Hedrick et al. (2015) conducted a large osteological revision of Nothronychus, concluding the genus was the most complete therizinosaurid.
Description[]
Nothronychus is built much like other therizinosaurs, like Therizinosaurus. It had a long neck to help it reach into the tops of trees and a small head to help pick out specific branches. It grew to be about 6 meters (20 feet) long, 3.4 meters (12 feet) tall, and one ton in weight. It had very long arms with long, impressive-looking sharp claws. Although these claws looked menacing, they were actually designed to get a grip on branches and bring them closer to the small head of this gluttonous herbivore. However, when threatened, they would make potentially deadly weapons. Nothronychus walked around on two thick, muscular hind legs, but it likely couldn't move fast. It had a short, but stocky tail that probably helped keep it balanced on its back legs. Most scientists also believe that Nothronychus and other therizinosaurs had downy feathers and potbellies, since they were herbivores. It may seem odd to think about, but Nothronychus and its relatives actually evolved from the raptor-like theropods, such as Velociraptor. Scientists aren't exactly sure when it occurred, but most speculate it was sometime during the early Cretaceous Period.
The genus has several autapomorphies: a prominent subcircular obturator formation, an elongate obturator foramen, the pubis and ischium constrict at the upper obturator, deep-cutting towards the lower facet of the obturator process and the the frontal ischial shaft. Both species are similarly-sized, having similar humeri (41.5-42.4 centimeters, 415-424 millimeters respectively). Nothronychus is pot-bellied, with long necks, stocky 4-toed hindlimbs and robust arms tipped with three 30 centimeter (300 millimeter) long scythe-like claws and dexterous hands. The tail is shortened, but more flexible, and in N. mckinleyi is more robust in the tail, less vertebrae detail and a more bent ulna than N. graffami.
A reconstruction of 40 to 50 percent of its skeleton, from two separate species, allowed scientists to describe these dinosaurs as having leaf-shaped teeth with circular roots, long necks, long arms with dexterous hands and 10 cm (4 in) curved claws on their fingers, large "pot-bellied" abdomens, stout hind legs, and relatively short tails. N. mckinleyi was different from N. graffami in being less robust as well as details of the vertebrae, and a more bent lower arm bone (ulna).[5]
Classification[]
Nothronychus is a coelurosaur, and further a maniraptoran. Though most coelurosaurs are carnivorous, some maniraptors evolved omnivory, and therizinosaurids herbivory.[5] It was bipedal and walked more upright than its carnivore ancestors. N. graffami weighed about a tonne, were 4.5-6 m (15-20 ft) long and stood 3-3.6 m (10-12 ft) tall, while N. mckinleyi was only slightly smaller.[2] N. mckinleyi was assigned Therizinosauridae in 2001 based on derived features. Lindsey Zanno (2010) performed a large, comprehensive analysis of Therizinosauria, recovering both species as a sister grouping. Most of the data Zanno used was also used by Hartman et al. (2019) when analyzing coelurosaurs. Nothronychus was a therizinosaurid with both species assuming a derived position. The results:
Nothronychus skeleton in side and front views
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Paleobiology and paleoecology[]
Bird-like characteristics and preserved feathers in fossils of its Asian relative Beipiaosaurus indicate Nothronychus may have had a primitive coat of feathers consisting of both short, down-like fibers as well as long, quill-like bristles. No feather impressions were found with the fossil remains, probably because the surrounding sediment was unable to preserve such delicate features.
The sloth-like Nothronychus lived in swampy forests similar to the 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.
Cranial endocast of N. mckinleyi
In 2018, the holotype's braincase was reassessed by Smith et al., noting it had a large pneumatic chambers at the sensorial locations, which would cause increased tympanic systems and, in return, could receive low frequency sounds, likely infrasound. This suggests a complex social life. The increased size in the cochlea and pneumatic chambers also support this observation. They also determined the average frequency of hearing in Nothronychus to be between 1100 and 1450 Hz, and upper estimates being from 3000 to 3700 Hz. However, they plainly stated that these estimates could be over exaggerated. N. mckinleyi possesses semicircular canals in their ears, which is usually a feature in active predators. This means that all therizinosaurid may have kept their ancestry hearing configuration, as suggested in Erlikosaurus. N. mckinleyi may have had a relatively horizontal head posture, which is associated with binocular vision and overlapping visual fields. Binocular vision can be determined via horizontal semicircular canals relative to the horizontal orientation of the occipital condyle.
JPInstitute.com Description[]
Nothronychus was a very strange looking plant-eater that evolved from a meat-eating dinosaur family. The discovery of Nothronychus has caused a lot of discussion among scientists. Before its discovery, this family of dinosaurs was known only from Asia.
It is closely related to Therizinosaurus, an Asian relative that was slightly larger. It may have had feathers as others in its family have been discovered with the remains of protofeathers in their fossils. This dinosaur has helped paint a picture of what life was like in the middle Cretaceous period in North America, a time period for which very few fossils have been discovered.
While the claws were very long, they were not very curved. In cross section they were also quite thin. One theory is that these claws were used to help it strip leaves from branches as well as being a formidable defensive weapon. Therizinosaurs had fairly long necks, small heads, and teeth that would have been used to eat plants.
Appearance in other media[]
Jurassic Park[]
- It appears as part of the Jurassic World: Primal Ops game for mobile devices.
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Read more Nothronychus on Jurassic Park Wiki |
The Land Before Time[]
- It was also seen as a character named Wild Arms featured in The Land Before Time XIV: Journey of the Brave.
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List of species in The Land Before Time |
Links[]
http://web.archive.org/web/20040806083539fw_/http://www.jpinstitute.com/dinopedia/dinocards/dc_nothr.html https://web.archive.org/web/20080705172048/http://kids.yahoo.com/dinosaurs/370--Nothronychus
References[]
https://en.wikipedia.org/wiki/Nothronychus
- ↑ 1.0 1.1 Kirkland, J.I., and Wolfe, D.G. (2001). "First definitive therizinosaurid (Dinosauria; Theropoda) from North America." Journal of Vertebrate Paleontology, 21(3): 410-414.
- ↑ 2.0 2.1 2.2 2.3 2.4 Gillette, D.D. (2007). "Therizinosaur: Mystery of the Sickle-Clawed Dinosaur." Arizona Geology, 37(2): 1-6. pdf available
- ↑ Albright, L.B. III, Gillette, D.D. and 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, abstract.
- ↑ Gillette, D.D., Albright, L.B. III, Titus, A.L., and 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, abstract.
- ↑ 5.0 5.1 5.2 Zanno, L.E., Gillette, D.D., Albright, L.B., and Titus, A.L. (2009). "A new North American therizinosaurid and the role of herbivory in 'predatory' dinosaur evolution." Proceedings of the Royal Society B, Published online before print July 15, 2009, doi: 10.1098/rspb.2009.1029.