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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 (MSM P2117) left humerus.Partial distal left humerus in (A) caudal, (B) distal, and (C) cranial views. Figure explanations on figure. Scale = 100 mm.
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pone.0129449.g021: Nothronychus (MSM P2117) left humerus.Partial distal left humerus in (A) caudal, (B) distal, and (C) cranial views. Figure explanations on figure. Scale = 100 mm.

Mentions: The right humerus of MSM P2117 (No. mckinleyi) is completely preserved although the distal end is craniocaudally compressed (Fig 20). The left humerus preserves only the distal end, but it is undistorted (Fig 21). UMNH VP16420 (No. graffami) preserves both humeri in their entirety, but they are craniocaudally compressed and the caudal surface is sheared (Fig 22). A hypertrophied internal tuberosity is a characteristic trait of therizinosauroids and is present in both species of Nothronychus [18]. The internal tuberosity in both species of Nothronychus most resembles Suzhousaurus [38] while Falcarius and Jianchangosaurus have relatively smaller internal tuberosities (although still well developed) [17, 30] and Neimongosaurus and Erliansaurus have relatively larger internal tuberosities [14, 15]. Therizinosaurus has a relatively smaller internal tuberosity than other therizinosaurids. Both Nothronychus specimens have a depression between the head of the humerus and the internal tuberosity both on the proximal and caudal sides [2]. Falcarius has a small tuberosity lateral to the humeral head [17] that is not seen in either species of Nothronychus.


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 (MSM P2117) left humerus.Partial distal left humerus in (A) caudal, (B) distal, and (C) cranial views. Figure explanations on figure. Scale = 100 mm.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0129449.g021: Nothronychus (MSM P2117) left humerus.Partial distal left humerus in (A) caudal, (B) distal, and (C) cranial views. Figure explanations on figure. Scale = 100 mm.
Mentions: The right humerus of MSM P2117 (No. mckinleyi) is completely preserved although the distal end is craniocaudally compressed (Fig 20). The left humerus preserves only the distal end, but it is undistorted (Fig 21). UMNH VP16420 (No. graffami) preserves both humeri in their entirety, but they are craniocaudally compressed and the caudal surface is sheared (Fig 22). A hypertrophied internal tuberosity is a characteristic trait of therizinosauroids and is present in both species of Nothronychus [18]. The internal tuberosity in both species of Nothronychus most resembles Suzhousaurus [38] while Falcarius and Jianchangosaurus have relatively smaller internal tuberosities (although still well developed) [17, 30] and Neimongosaurus and Erliansaurus have relatively larger internal tuberosities [14, 15]. Therizinosaurus has a relatively smaller internal tuberosity than other therizinosaurids. Both Nothronychus specimens have a depression between the head of the humerus and the internal tuberosity both on the proximal and caudal sides [2]. Falcarius has a small tuberosity lateral to the humeral head [17] that is not seen in either species of Nothronychus.

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.