Morphometric variability of the precaudal vertebrae of Thamnophis sirtalis sirtalis (Serpentes: Colubridae), and implications for interpretation of the fossil record.
Item
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Title
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Morphometric variability of the precaudal vertebrae of Thamnophis sirtalis sirtalis (Serpentes: Colubridae), and implications for interpretation of the fossil record.
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Identifier
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AAI9207090
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identifier
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9207090
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Creator
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LaDuke, Thomas C.
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Contributor
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Adviser: Max K. Hecht
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Date
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1991
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Language
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English
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Publisher
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City University of New York.
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Subject
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Biology, Zoology | Biology, Anatomy | Biology, Ecology
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Abstract
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Snake vertebrae are biologically interesting structures because of the important roles they play in the functional morphology, axial development, and paleontology of snakes. Yet, morphometric variability of these structures, both among and within taxa, is very poorly understood. This study lays a foundation for future comparative work by addressing several points about variability of shape of precaudal vertebrae of Thamnophis s. sirtalis: (1) Empirical studies of three different modes of comparison of vertebrae among snakes with different numbers of precaudal vertebrae demonstrate that axial positional identity is determined by the percentage position of a vertebra along the column (vertebra number/total vertebral count). Sequential positions determined with respect to the cranial or caudal ends of the precaudal column are not comparable among columns with different precaudal counts. (2) Similar sized snakes with differing vertebral counts must pack their vertebrae into the same space. Graphic comparisons suggest that this is accomplished by a relative shortening of vertebrae in snakes with higher vertebral counts. An alternative model in which relative vertebral length is unchanged, and snakes with higher vertebral counts are longer, is rejected. (3) Examination of vertebral growth trends in these snakes, suggests that growth in width and height dimensions is negatively allometric, but does not follow a geometrically simple trajectory. A change in the nature of vertebral growth appears to affect females as they grow beyond the size of reproductive maturity, such that length dimensions grow at a constant rate, relative to body length, but width and height dimensions grow at a lower rate above the size of reproductive maturity. (4) Sexual dimorphism in the vertebrae of similar sized Thamnophis s. sirtalis manifests itself in the relative size of the cotyle-condyle articular joint, which is larger in females.;It is concluded that vertebrae vary in a tightly controlled, regimented fashion that should be highly tractable, allowing shape to be modeled quantitatively. In some cases, precise statements as to the age and sex of fossil specimens should be possible. Although interspecific variability has not been addressed, it is hoped that similar precision will be available for discrimination of taxa.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
