EVIDENCE FOR ONTOGENETIC SHAPE CHANGE IN A JUVENILE SKULL OF DIPLODOCUS (original) (raw)

Abstract

The diplodocoid sauropods have been defined in large part by their blunt, shovel-snouted skulls and their narrow-crowned, anteriorly sequestered dentition. This arrangement of the snout and teeth has also been the focus of some controversy, and hypotheses abound to explain the function of this anatomy for feeding. Here we describe a nearly complete juvenile skull of Diplodocus (CM 11255) which does not conform to the morphology expected based upon larger specimens. Although somewhat laterally crushed, the skull is still largely intact, and CT imaging has revealed a nearly complete palate, allowing an accurate reconstruction of the lateral dimensions of the skull. In dorsal view, the reconstructed CM 11255 is narrower than would be expected and quite rounded anteriorly, in contrast to the characteristic squared-off snout of adult Diplodocus. The dentition in CM 11255 is also not restricted to the extreme anterior portion of the skull, and in fact extends posteriorly to near the preantorbital fenestra. A rounded snout in dorsal view is more typical of basal sauropods, and ontogenetic change towards a square snout is potentially related to feeding behavior and specialization in adults. Work comparing snout shapes and dental microwear features between different diplodocoid sauropod genera (including Diplodocus) suggests that snout shape is closely linked to feeding strategy. Although no microwear features have been recovered from CM 11255, the shape change suggests ontogenetic niche partitioning between adults and juveniles is suggested—smaller juveniles accessed nutrients through highly selective browsing behaviors, and large adults obtained nutrition through less selective, bulk browsing behaviors.

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