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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) right ischium.Right ischium in (A) lateral and (B) medial views. Figure explanations on figure. Scale = 100 mm. The (C) pubic and (D) iliac articulations shown closer. Scale = 50 mm.
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pone.0129449.g028: Nothronychus (MSM P2117) right ischium.Right ischium in (A) lateral and (B) medial views. Figure explanations on figure. Scale = 100 mm. The (C) pubic and (D) iliac articulations shown closer. Scale = 50 mm.

Mentions: Both ischia are preserved for MSM P2117 (No. mckinleyi) (Fig 28) and UMNH VP16420 (No. graffami) (Fig 29), but they are partial for UMNH VP16420. Therefore, the description primarily follows MSM P2117. The ischia of both specimens are characteristic for derived therizinosaurians by virtue of the expanded obturator process. The subcircular obturator process found in both species of Nothronychus differentiates Nothronychus from other therizinosaurian genera. The ischia are subequal in size to the pubes not considering the size of the pubic boot. This character is also seen to a lesser degree in less specialized therizinosaurian forms [18, 30]. The obturator process is broken in Falcarius, but shows slight expansion suggesting hypertrophy of the process only developed in more derived forms [18]. This is further supported by the modest development of the obturator process in Jianchangosaurus [30]. In contrast with Falcarius, the shafts of the ischia of MSM P2117 are straight as in Jianchangosaurus, Suzhousaurus, and Segnosaurus. However, both Nothronychus species have a deep notch separating the ischial shaft and obturator process unlike other therizinosaurians. This is narrower in MSM P2117 than in UMNH VP16420 and serves as a feature distinguishing the two species. As in other therizinosaurians, the iliac and pubic peduncles are flattened medially and expanded laterally. The iliac and pubic peduncles are approximately equal in length (length iliac peduncle: 73.5 mm; length pubic peduncle: 74.3 mm). The iliac peduncle is twice the length of the pubic peduncle in Falcarius [18]. They are subequal in Segnosaurus [6] and Suzhousaurus [44], which may reflect an evolutionary trend toward the development of a more robust ischium in therizinosaurians. There is a dorsally projecting prominence between the peduncles, which forms the ischiadic portion of the acetabulum. The prominence is substantial in MSM P2117, but shows that the ischium does not contribute a significant portion of the acetabulum similar to other therizinosaurids and Suzhousaurus.


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) right ischium.Right ischium in (A) lateral and (B) medial views. Figure explanations on figure. Scale = 100 mm. The (C) pubic and (D) iliac articulations shown closer. Scale = 50 mm.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0129449.g028: Nothronychus (MSM P2117) right ischium.Right ischium in (A) lateral and (B) medial views. Figure explanations on figure. Scale = 100 mm. The (C) pubic and (D) iliac articulations shown closer. Scale = 50 mm.
Mentions: Both ischia are preserved for MSM P2117 (No. mckinleyi) (Fig 28) and UMNH VP16420 (No. graffami) (Fig 29), but they are partial for UMNH VP16420. Therefore, the description primarily follows MSM P2117. The ischia of both specimens are characteristic for derived therizinosaurians by virtue of the expanded obturator process. The subcircular obturator process found in both species of Nothronychus differentiates Nothronychus from other therizinosaurian genera. The ischia are subequal in size to the pubes not considering the size of the pubic boot. This character is also seen to a lesser degree in less specialized therizinosaurian forms [18, 30]. The obturator process is broken in Falcarius, but shows slight expansion suggesting hypertrophy of the process only developed in more derived forms [18]. This is further supported by the modest development of the obturator process in Jianchangosaurus [30]. In contrast with Falcarius, the shafts of the ischia of MSM P2117 are straight as in Jianchangosaurus, Suzhousaurus, and Segnosaurus. However, both Nothronychus species have a deep notch separating the ischial shaft and obturator process unlike other therizinosaurians. This is narrower in MSM P2117 than in UMNH VP16420 and serves as a feature distinguishing the two species. As in other therizinosaurians, the iliac and pubic peduncles are flattened medially and expanded laterally. The iliac and pubic peduncles are approximately equal in length (length iliac peduncle: 73.5 mm; length pubic peduncle: 74.3 mm). The iliac peduncle is twice the length of the pubic peduncle in Falcarius [18]. They are subequal in Segnosaurus [6] and Suzhousaurus [44], which may reflect an evolutionary trend toward the development of a more robust ischium in therizinosaurians. There is a dorsally projecting prominence between the peduncles, which forms the ischiadic portion of the acetabulum. The prominence is substantial in MSM P2117, but shows that the ischium does not contribute a significant portion of the acetabulum similar to other therizinosaurids and Suzhousaurus.

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.