Abstract

Morphometric analyses of sauropod limbs have the potential to illuminate functional aspects of sauropod locomotion and paleobiology. However, analyses of sauropod limb dimensions typically show few discernible morphological trends because of large size differences among the individuals in a sample. For sauropods, combined analyses of both limb dimension and shape may be more desirable. Numerous humeri and femora from Apatosaurus, Diplodocus, and Camarasaurus provide an opportunity to explore and compare limb morphology in contemporaneous, sympatric sauropods. Thin-plate splines were used to analyze landmark-based shape differences in combination with traditional morphometrics. The aims of the analysis were (1) to determine if humerus and femur shape were significantly different among the genera; (2) to determine where shape changes occurred; and (3) to infer the basic functional implications of the shape differences using an Extant Phylogenetic Bracket approach. Few differences were detected among the genera using traditional morphometric analyses, and linear regression revealed a predominantly isometric relationship between most measurement variables and element size. Thin-plate splines revealed significant shape differences among the taxa. Apatosaurus humeri and femora were the most robust, with expanded regions for muscle insertion and more distally placed deltopectoral and caudofemoral landmarks. Diplodocus humeri and femora were gracile, with more proximally located landmarks of muscular insertion. Camarasaurus humeri were surprisingly gracile, with a less extensive deltopectoral crest, but had more robust femora similar to those of Apatosaurus. Few differences distinguished juvenile from adult specimens. These data suggest some locomotor differences were present among the three genera.

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