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The Slothful Claw: Osteology and Taphonomy of Nothronychus mckinleyi and N. graffami (Dinosauria: Theropoda) and Anatomical Considerations for Derived Therizinosaurids.

Hedrick BP, Zanno LE, Wolfe DG, Dodson P - PLoS ONE (2015)

Bottom Line: In spite of the biogeographical and evolutionary importance of these two taxa, neither has received a detailed description.However, here we present the difference as much more likely related to diagenetic compression in No. graffami rather than as a true biologic difference.Finally, we include copies of three-dimensional surface scans of all major bones for both taxa for reference.

View Article: PubMed Central - PubMed

Affiliation: Department of Earth and Environmental Science, University of Pennsylvania, Philadelphia, PA, United States of America.

ABSTRACT
Nothronychus was the first definitive therizinosaurian discovered in North America and currently represents the most specialized North American therizinosaurian genus. It is known from two species, No. mckinleyi from the Moreno Hill Formation (middle Turonian) in west-central New Mexico, and No. graffami from the Tropic Shale (early Turonian) in south-central Utah. Both species are represented by partial to nearly complete skeletons that have helped elucidate evolutionary trends in Therizinosauria. In spite of the biogeographical and evolutionary importance of these two taxa, neither has received a detailed description. Here, we present comprehensive descriptions of No. mckinleyi and No. graffami, the latter of which represents the most complete therizinosaurid skeleton known to date. We amend previous preliminary descriptions of No. mckinleyi and No. graffami based on these new data and modify previous character states based on an in-depth morphological analysis. Additionally, we review the depositional history of both specimens of Nothronychus and compare their taphonomic modes. We demonstrate that the species were not only separated geographically, but also temporally. Based on ammonoid biozones, the species appear to have been separated by at least 1.5 million years and up to 3 million years. We then discuss the impacts of diagenetic deformation on morphology and reevaluate potentially diagnostic characters in light of these new data. For example, the ulna of No. mckinleyi is curved whereas the ulna of No. graffami was considered straight, a character originally separating the two species. However, here we present the difference as much more likely related to diagenetic compression in No. graffami rather than as a true biologic difference. Finally, we include copies of three-dimensional surface scans of all major bones for both taxa for reference.

No MeSH data available.


Nothronychus (UMNH VP16420) cervical vertebrae.(A) Poorly preserved caudal cervical. (B) Poorly preserved caudal cervical. Scale = 100 mm.
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pone.0129449.g004: Nothronychus (UMNH VP16420) cervical vertebrae.(A) Poorly preserved caudal cervical. (B) Poorly preserved caudal cervical. Scale = 100 mm.

Mentions: There are numerous cervical vertebral elements associated with MSM P2117 (No. mckinleyi) representing a minimum of seven vertebrae and two partial cervicals preserved with UMNH VP16420 (No. graffami). However, all of the cervical vertebrae in both taxa are badly diagenetically distorted and fragmentary (Figs 4 and 5). As such, it is not possible to determine the exact position of any vertebra. The length of the cervical column is not well known in therizinosaurians, though many of the known taxa preserve several cervical vertebrae. Jianchangosaurus (n = 10), Beipiaosaurus (STM31-1 [Shandong Tianyu Museum of Nature, Shandong, China]) (n = 9), Nanshiungosaurus (n = 11), and Neimongosaurus (n = 13) are the only articulated therizinosauroids known that preserve all of their cervical vertebrae [7, 14, 30, 35]. Neimongosaurus and Nanshiungosaurus bracket Nothronychus phylogenetically [19] providing a possible upper and lower bound for the cervical vertebral count. Numerous cervical vertebrae are known for Falcarius [18], but the actual vertebral count is unknown, as all Falcarius material is known from a disarticulated bonebed. Five cervicals are known from Alxasaurus, but they are not articulated and do not represent a complete column [12].


The Slothful Claw: Osteology and Taphonomy of Nothronychus mckinleyi and N. graffami (Dinosauria: Theropoda) and Anatomical Considerations for Derived Therizinosaurids.

Hedrick BP, Zanno LE, Wolfe DG, Dodson P - PLoS ONE (2015)

Nothronychus (UMNH VP16420) cervical vertebrae.(A) Poorly preserved caudal cervical. (B) Poorly preserved caudal cervical. Scale = 100 mm.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4465624&req=5

pone.0129449.g004: Nothronychus (UMNH VP16420) cervical vertebrae.(A) Poorly preserved caudal cervical. (B) Poorly preserved caudal cervical. Scale = 100 mm.
Mentions: There are numerous cervical vertebral elements associated with MSM P2117 (No. mckinleyi) representing a minimum of seven vertebrae and two partial cervicals preserved with UMNH VP16420 (No. graffami). However, all of the cervical vertebrae in both taxa are badly diagenetically distorted and fragmentary (Figs 4 and 5). As such, it is not possible to determine the exact position of any vertebra. The length of the cervical column is not well known in therizinosaurians, though many of the known taxa preserve several cervical vertebrae. Jianchangosaurus (n = 10), Beipiaosaurus (STM31-1 [Shandong Tianyu Museum of Nature, Shandong, China]) (n = 9), Nanshiungosaurus (n = 11), and Neimongosaurus (n = 13) are the only articulated therizinosauroids known that preserve all of their cervical vertebrae [7, 14, 30, 35]. Neimongosaurus and Nanshiungosaurus bracket Nothronychus phylogenetically [19] providing a possible upper and lower bound for the cervical vertebral count. Numerous cervical vertebrae are known for Falcarius [18], but the actual vertebral count is unknown, as all Falcarius material is known from a disarticulated bonebed. Five cervicals are known from Alxasaurus, but they are not articulated and do not represent a complete column [12].

Bottom Line: In spite of the biogeographical and evolutionary importance of these two taxa, neither has received a detailed description.However, here we present the difference as much more likely related to diagenetic compression in No. graffami rather than as a true biologic difference.Finally, we include copies of three-dimensional surface scans of all major bones for both taxa for reference.

View Article: PubMed Central - PubMed

Affiliation: Department of Earth and Environmental Science, University of Pennsylvania, Philadelphia, PA, United States of America.

ABSTRACT
Nothronychus was the first definitive therizinosaurian discovered in North America and currently represents the most specialized North American therizinosaurian genus. It is known from two species, No. mckinleyi from the Moreno Hill Formation (middle Turonian) in west-central New Mexico, and No. graffami from the Tropic Shale (early Turonian) in south-central Utah. Both species are represented by partial to nearly complete skeletons that have helped elucidate evolutionary trends in Therizinosauria. In spite of the biogeographical and evolutionary importance of these two taxa, neither has received a detailed description. Here, we present comprehensive descriptions of No. mckinleyi and No. graffami, the latter of which represents the most complete therizinosaurid skeleton known to date. We amend previous preliminary descriptions of No. mckinleyi and No. graffami based on these new data and modify previous character states based on an in-depth morphological analysis. Additionally, we review the depositional history of both specimens of Nothronychus and compare their taphonomic modes. We demonstrate that the species were not only separated geographically, but also temporally. Based on ammonoid biozones, the species appear to have been separated by at least 1.5 million years and up to 3 million years. We then discuss the impacts of diagenetic deformation on morphology and reevaluate potentially diagnostic characters in light of these new data. For example, the ulna of No. mckinleyi is curved whereas the ulna of No. graffami was considered straight, a character originally separating the two species. However, here we present the difference as much more likely related to diagenetic compression in No. graffami rather than as a true biologic difference. Finally, we include copies of three-dimensional surface scans of all major bones for both taxa for reference.

No MeSH data available.