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Shell Morphology of North American Tortoises

David J. Germano
The American Midland Naturalist
Vol. 129, No. 2 (Apr., 1993), pp. 319-335
DOI: 10.2307/2426513
Stable URL: http://www.jstor.org/stable/2426513
Page Count: 17
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Shell Morphology of North American Tortoises
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Abstract

Significant differences exist in adult carapace lengths among the four species of North American tortoises (Gopherus spp.). However, after measures of whole shell and scute dimensions are adjusted for these size differences, shape is more similar between the largest species, G. flavomarginatus, and the smallest species, G. berlandieri, than with either of the intermediate-sized species, G. polyphemus and G. agassizii. Recent data based on an analysis of mitochondrial DNA of North American tortoises provide a phylogeny of the four extant species. A phenogram based on a multivariate analysis of 31 scute and shell measurements of North American tortoises is not concordant with a phenogram based on genetic data, although relationships among three major populations of G. agassizii are the same. Morphometric data are also not concordant with a matrix based on measures of precipitation and temperature, but are significantly correlated with a matrix based on growth variables (R2 = 0.74, P = 0.029). Other environmental parameters may affect shape of shells.

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