Dissertation/Thesis Abstract

Functional morphology of the atlas in primates and its implications for reconstructing posture in fossil taxa
by Parks, Hillary L., M.S., Western Illinois University, 2012, 66; 1517124
Abstract (Summary)

Primates are a diverse group of eutherian mammals that employ a variety of postures and locomotor modes. Some hold the vertebral column upright (orthograde), whereas others retain a horizontal vertebral orientation (pronograde). Since body posture and locomotion can inform paleontologists about an animal's habits in life, it is integral to develop methods that use fossil remains to ascertain the state of such behaviors in extinct taxa. Here, the potential locomotor and postural behaviors of the fossil adapiform Leptadapis magnus are determined via two dimensional geometric morphometric (thin plate splines) techniques applied to the first cervical vertebra, or atlas. Leptadapis magnus is a well-known European fossil primate assumed to have had a pronograde posture and arboreal quadrupedal or intentional climbing locomotor behaviors. Atlas shape is related to posture and locomotor modes in extant primate taxa, and therefore shape variation in extinct taxa should reflect these attributes as well. Two dimensional data were gathered from photographs of the superior and inferior faces of primate atlases which were then digitized with eight landmarks. Analytical methods including thin plate spline regression and relative warps analysis for shape analysis, principal component analysis, Anderson's test, and discriminate factor analysis were used to suggest the locomotor and postural behaviors of L. magnus. Additional hypotheses regarding the significant differences in atlas shape among primate taxonomic, locomotor, and postural groups and the usefulness of the atlas as a tool to infer the place of primate fossil specimens among these categories was also tested. The atlas is a good anatomical proxy for indicating these behaviors because it is an integral component of the atlanto-occipital and atlantoaxial joints and its function, a point of attachment for muscles that control the movement of the head and neck, has a direct effect on its form. The form of the atlas controls the range of motion possible for the head and neck and therefore limits the locomotor and postural modes that can be employed. The shape of the first cervical vertebra is shown to be significantly different among taxonomic, locomotor, and postural primate groups based on a broad sample (N=173). Although significant differences in atlas shape were found among the categories, only the first principal component from the inferior dataset was found to be the source of significant difference. The results suggest that the morphology of the inferior surface of the atlas is likely indicative of locomotor and postural modes. Trends reported here also suggest that the effect of locomotor modes on the morphology of the inferior face of the atlas affects the inferior postural and taxonomic groupings. Discriminate factor analysis was used to determine the locomotor and postural modes of extant primates based on their atlas morphology. The accuracy of the discriminate factor analysis for extant primates allows us to support the assumption that L. magnus was a pronograde, arboreal quadruped.

Indexing (document details)
Advisor: Bonnan, Matthew F., White, Jessica L.
Commitee: Meiers, Susan T.
School: Western Illinois University
Department: Biology
School Location: United States -- Illinois
Source: MAI 51/02M(E), Masters Abstracts International
Source Type: DISSERTATION
Subjects: Morphology, Paleontology, Behavioral Sciences
Keywords: Atlas, Fossil primates, Geometric morphometrics, Leptadapis magnus, Locomotor modes, Postural modes
Publication Number: 1517124
ISBN: 9781267572394
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