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Morphological diversity in the postcranial skeleton of Casamayoran (?middle to late Eocene) Notoungulata and foot posture in notoungulates ; American Museum novitates, no. 3601

Show simple item record Shockey, Bruce J. en_US Flynn, John J. (John Joseph), 1955- en_US 2007-12-18T17:39:04Z 2007-12-18T17:39:04Z 2007 en_US
dc.description 26 p. : ill. ; 26 cm. en_US
dc.description Includes bibliographical references (p. 24-26). en_US
dc.description.abstract Appendicular skeletons of isotemnid notoungulates are described from Cañadón Vaca (Vacan "subage", Casamayoran South American Land Mammal "Age", ?middle to late Eocene). Simpson documented three of these, Thomashuxleya externa, Anisotemnus distentus, and Pleurostylodon similis, some 70 years ago, in fashioning a composite isotemnid skeleton, but he did not emphasize their differences from one another. We note variation, especially in the forelimb, that appears to be functionally significant as well as phylogenetically informative. For example, the downwardly curved olecranon, ventrally concave bowing of the ulnar shaft, and orthogonally directed articulation of the elbow joint suggest an erect forelimb stance in Thomashuxleya externa, whereas the forelimbs of Anisotemnus distentus and Pleurostylodon similis show indications of a crouching posture, including ventrally convex bowing of the ulnar shaft with a slight upward curvature of the olecranon, and an elbow joint in which the antebrachium rotated obliquely relative to the humerus. Articular facets on the proximal carpals suggest that the manus of Anisotemnus was habitually extended, indicating a plantigrade stance of the forelimb. Although none of these three taxa have associated hindfoot material, all known Vacan notoungulate astragali have shallow trochlea, well developed and deep grooves for the flexor hallucis longus, which are separated from the trochlea by a fossa that contains a superior astragalar foramen. An isolated notoungulate pes, not referred to any of the three taxa above, appears to be pentadactyl, having a distinctive, divergent tarsometatarsal joint for its hallux. It also has a shallow trochlea, an astragalar foramen, and a flexor groove, indicating limited rotation of the upper ankle joint. Indeed, a survey of known Casamayoran-aged notoungulate astragali indicates that most taxa had limited mobility at the tibioastragalar joint, in stark contrast to post-Eocene faunas in which nearly all the ungulates had greater rotation of the upper ankle joint and were subcursorial, as evidenced by their longer and deeper trochlear articulation and loss of the astragalar foramen. We suggest that the change from ambulatory- to subcursorial-dominated ungulate faunas across the Eocene-Oliogocene boundary mirrors the changes from brachydont to hypsodont faunas over the same time. Decreased temperatures and rainfall resulting in more open habitats may be related to both morphological evolutionary patterns. en_US
dc.format.extent 4732926 bytes
dc.format.mimetype application/pdf
dc.language eng en_US
dc.language.iso en_US
dc.publisher New York, NY : American Museum of Natural History en_US
dc.relation.ispartofseries American Museum novitates, no. 3601 en_US
dc.subject.lcc QL1 .A436 no.3601 2007 en_US
dc.subject.lcsh Notoungulata -- Argentina -- Chubut -- Morphology. en_US
dc.subject.lcsh Notoungulata -- Variation -- Argentina -- Chubut. en_US
dc.subject.lcsh Foot -- Anatomy. en_US
dc.subject.lcsh Forelimb. en_US
dc.subject.lcsh Notoungulata -- Locomotion. en_US
dc.subject.lcsh Mammals, Fossil -- Argentina -- Chubut. en_US
dc.subject.lcsh Paleontology -- Eocene -- Argentina -- Chubut. en_US
dc.subject.lcsh Paleontology -- Argentina -- Chubut. en_US
dc.title Morphological diversity in the postcranial skeleton of Casamayoran (?middle to late Eocene) Notoungulata and foot posture in notoungulates ; American Museum novitates, no. 3601 en_US
dc.title.alternative Morphological diversity in notoungulates en_US
dc.type text en_US

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  • American Museum Novitates
    Novitates (Latin for "new acquaintances"), published continuously and numbered consecutively since 1921, are short papers that contain descriptions of new forms and reports in zoology, paleontology, and geology. New numbers are published at irregular intervals.

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