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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) pedal ungual.Pedal ungual in side views. Digit unknown. Scale = 100 mm.
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pone.0129449.g037: Nothronychus (MSM P2117) pedal ungual.Pedal ungual in side views. Digit unknown. Scale = 100 mm.

Mentions: A total of eleven pedal phalanges are preserved with UMNH VP16420 (No. graffami) and three are associated with MSM P2117 (No. mckinleyi). Considering the higher degree of completion of the pes in UMNH VP16420, the discussion of pedal phalanges follows UMNH VP16420 since there are no clear morphological differences between the pes of the two species. Following Zanno et al. [2], the right foot is missing I-2, III-2, III-4, and IV-5 (Fig 36). The proximal phalanx of digit I is preserved. Proximally it is bowl-shaped and not bifurcated. Distally, there are two distinct condyles with deep collateral ligament pits as in Segnosaurus and Therizinosaurus [5, 6]. The left PI-1 is preserved for MSM P2117 and is similar in size and shape to PI-1 in UMNH VP16420. Digit II preserves PII-1 and PII-2. PII-1 is the largest phalanx preserved as in Therizinosaurus [5]. The ligament pits on PII-1 are less pronounced than in PI-1, but otherwise PII-1 has the same shape as PI-1. PII-2 is approximately the same size as PI-1, but has a different proximal surface for articulation with the two distal condyles of PII-1. PII-2 is nearly subequal in length with PII-1, but is much less robust. PIII-1 is identical to PII-1. PIII-2 is missing. PIII-3 is identical to PII-2. In Alxasaurus, there are no ligamentous pits on these phalanges [12], but they are present on UMNH VP16420. PIV-1 is the smallest proximal phalanx and is two-thirds the length of II-1 and III-1 as in Falcarius and Therizinosaurus [5, 18], while maintaining the same robusticity of the proximal and distal surfaces. PIV-2, PIV-3, and PIV-4 are preserved and are progressively smaller than PIV-1. Based on the similarities to UMNH VP16420, it is possible to refer the remaining two small phalanges preserved with MSM P2117 to PIV-2 and PIV-4. Two pedal unguals are preserved in MSM P2117 and one in UMNH VP16420. The pedal unguals in both specimens are robust, though are substantially smaller than the manual unguals as in other therizinosaurians (Fig 37). They are approximately the same length as the pedal phalanges and are gently recurved. The pedal unguals are transversely expansive rather than compressed like the manual unguals. This robusticity is especially evident on the articulation facets.


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) pedal ungual.Pedal ungual in side views. Digit unknown. Scale = 100 mm.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0129449.g037: Nothronychus (MSM P2117) pedal ungual.Pedal ungual in side views. Digit unknown. Scale = 100 mm.
Mentions: A total of eleven pedal phalanges are preserved with UMNH VP16420 (No. graffami) and three are associated with MSM P2117 (No. mckinleyi). Considering the higher degree of completion of the pes in UMNH VP16420, the discussion of pedal phalanges follows UMNH VP16420 since there are no clear morphological differences between the pes of the two species. Following Zanno et al. [2], the right foot is missing I-2, III-2, III-4, and IV-5 (Fig 36). The proximal phalanx of digit I is preserved. Proximally it is bowl-shaped and not bifurcated. Distally, there are two distinct condyles with deep collateral ligament pits as in Segnosaurus and Therizinosaurus [5, 6]. The left PI-1 is preserved for MSM P2117 and is similar in size and shape to PI-1 in UMNH VP16420. Digit II preserves PII-1 and PII-2. PII-1 is the largest phalanx preserved as in Therizinosaurus [5]. The ligament pits on PII-1 are less pronounced than in PI-1, but otherwise PII-1 has the same shape as PI-1. PII-2 is approximately the same size as PI-1, but has a different proximal surface for articulation with the two distal condyles of PII-1. PII-2 is nearly subequal in length with PII-1, but is much less robust. PIII-1 is identical to PII-1. PIII-2 is missing. PIII-3 is identical to PII-2. In Alxasaurus, there are no ligamentous pits on these phalanges [12], but they are present on UMNH VP16420. PIV-1 is the smallest proximal phalanx and is two-thirds the length of II-1 and III-1 as in Falcarius and Therizinosaurus [5, 18], while maintaining the same robusticity of the proximal and distal surfaces. PIV-2, PIV-3, and PIV-4 are preserved and are progressively smaller than PIV-1. Based on the similarities to UMNH VP16420, it is possible to refer the remaining two small phalanges preserved with MSM P2117 to PIV-2 and PIV-4. Two pedal unguals are preserved in MSM P2117 and one in UMNH VP16420. The pedal unguals in both specimens are robust, though are substantially smaller than the manual unguals as in other therizinosaurians (Fig 37). They are approximately the same length as the pedal phalanges and are gently recurved. The pedal unguals are transversely expansive rather than compressed like the manual unguals. This robusticity is especially evident on the articulation facets.

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.