Nothronychus
Name:
Nothronychus
(slothful claw).
Phonetic: Nof-ron-e-kus.
Named By: J. I. Kirkland & D. G.
Wolfe - 2001.
Classification: Chordata, Reptilia, Dinosauria,
Saurischia, Theropoda, Maniraptora, Therizinosauridae.
Species: N. mckinleyi
(type), N. graffami.
Diet: Herbivore.
Size: Estimated between 4.5-6 meters long.
Known locations: USA, New Mexico - Moreno Hill
Formation, and Utah - Tropic Shale Formation.
Time period: Late Cenomanian to Early Turonian of
the Cretaceous.
Fossil representation: Remains of two individuals,
each representing a distinct species.
First
described in 2001, Nothronychus was the first
genus of
therizinosaurid
dinosaur to be discovered in North America (the state
of New Mexico in the USA), with other earlier notable discoveries
such as Beipiaosaurus
and Therizinosaurus
being discovered in China and
Mongolia. However the first fossil of Nothronychus
called an ischium
(the rear downward projection on the pelvis), was first
interpreted as being a squamosal bone of the ceratopsian
dinosaur
Zuniceratops
(squamosals on ceratopsian dinosaurs form the outer
edges of the neck frill). More study of both this ischium and the
fossil location soon revealed further remains of a then unknown genus
of dinosaur, and the remains of this individual would become the
holotype specimen of Nothronychus.
Therizinosaurid
dinosaurs are noted for having very large claws on the tips of their
fingers, and most palaeontologists agree that these claws would have
been used to hook around branches to facilitate feeding in a similar
manner to how you can see a sloth use its long claws to do just this
today. This was the inspiration for the name Nothronychus
which
roughly means ‘slothful claw’ the type species name N.
mckinleyi
is in honour of the land owner where the Nothronychus
type fossil was
found, Bobby McKinley. It was only one year later however that
another Nothronychus specimen was found, this
time in Utah. This
individual would later be named as a second species of Nothronychus
named N. graffami in 2009, and in honour the
discoverer, M.
H. Graffam.
Between
these two species, N. mckinleyi seems to
have been a little
smaller and noticeably less robust in build that N. graffami.
Finer
details between them include N. mckinleyi having
a more pronounced
bend in the lower arm, as well as differences in the caudal (tail)
vertebrae. Beyond this though, both species of Nothronychus
display what has become the classic therizinosaurid body form, of a
squat bipedal theropod dinosaur with a large belly, for a much larger
digestive system (essential for digesting plant material that takes
longer to digest than meat). Actual feeding adaptations include
proportionately long necks for reach, and claws on fingers to pull on
branches so that an individual can reach taller growths. Nothronychus
is known to have leaf shaped teeth which would have been ideal for
slicing up soft plants, while there is also speculation that
Nothronychus would have also had a keratinous beak.
An
interesting side note about Nothronychus graffami
is that the type
specimen for this species was recovered from a marine deposit. This
means that this individual Nothronychus had somehow
been swept out to
sea and finally come to rest on the bottom of what would then have been
known as the Western Interior Seaway, the shallow sea that once
submerged central North America from Mexico all the way into Canada,
dividing North America into western and eastern landmasses called
Laramidia and Appalachia respectively.
Further reading
- First definitive therizinosaurid (Dinosauria; Theropoda) from
North America. - Journal of Vertebrate Paleontology, 21(3):
410-414. - J. I. Kirkland & D. G. Wolfe -
2001.
- 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. - L. B.
Albright III, D. D. Gillette & A. L. Titus -
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. - D. D. Gillette,
L. B. Albright III, A. L. Titus & M. H.
Graffam - 2002.
- A new North American therizinosaurid and the role of herbivory in
'predatory' dinosaur evolution. - Proceedings of the Royal
Society B: Biological Sciences - L. E. Zanno, D. D.
Gillette, L. B. Albright & A. L. Titus - 2009.
- A re-evaluation of the basicranial soft tissues and pneumaticity of
the therizinosaurian Nothronychus mckinleyi (Theropoda; Maniraptora). -
PLOS ONE. 13 (7): e0198155. - D. K. Smith, R. K. Sanders & D.
G. Wolfe - 2018.
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