A new multi-faceted framework for deciphering Diplodocid ontogeny

Abstract

Since sauropod dinosaurs lack the extravagant cranial features that are important to tracking ontogenetic trajectories (changes through growth), sauropods generally garner less focus on development than those dinosaurs with expressive cranial displays. The apparent lack of features that radically change through ontogeny has even led some to speculate that sauropods exhibited isometric growth. Yet within the past decade a small number of morphologic features have been demonstrated to undergo significant morphologic change; thus maturity can be tracked in ways other than histologic analysis (bone microstructure). The recognition of features that change dramatically through ontogeny hints at significant phylogenetic and biomechanical consequences in the immature sauropod condition. However the topic of morphologic ontogenetic change in sauropods is highly debated, with some question as to the validity of these apparent patterns. The current study will attempt to recognize additional morphologic and histologic features that can be used to infer maturity in diplodocid sauropods. By examining a broad range of features that span every aspect of the skeleton, the goal of this analysis is to substantiate previous ontogenetic inferences and conclusions. The findings of this analysis indicate that contrary to previous notions, diplodocid sauropods underwent radical ontogenetic changes in several skeletal elements. This analysis also establishes a suite of morphologic and histologic attributes that in combination can be used as a guide to identify maturational status in other diplodocid specimens. In addition this study also raises question to the validity of small bodied sauropod specimens that were previously recognized as distinct species.