Abstract
Most of the shark fossil record consists of teeth, due to their relative abundance, decay‐resistant enameloid, and the poor preservation potential of cartilaginous skeletons. However, rare cartilage fossils have changed our understanding of chondrichthyan evolution. Sharks have traditionally been considered primitive vertebrates, but new paleontological information demonstrates that chondrichthyans are actually a highly specialized group of fishes. In addition to valuable phylogenetic characters from fossil cartilage, three‐dimensionally preserved specimens allow us to explore functional morphology in extinct taxa. Here, we reconstruct jaw movement and musculature of the xenacanth Orthacanthus texensis. The cranium and jaws of Orthacanthus have been previously described, but a complete three‐dimensional specimen from the Permian of Texas (MCZ 12872) has never been addressed in its entirety. To better understand xenacanth anatomy, we took three‐dimensional surface scans of Orthacanthus skeletal elements by laser scanning, and articulated each element in Maya. We reconstructed musculature based on comparisons with several dissections of extant taxa, and then used Software for Interactive Musculoskeletal Modeling (SIMM) and OpenSim to assess muscle moment arms, potential functions, and optimal positioning for increasing bite forces. We find that Orthacanthus had large, extensive adductor muscles. To our knowledge, this is the first time SIMM has been used to model extinct chondrichthyan musculature. Computer modeling is an important method for this type of study, as xenacanths are not closely related to any modern sharks, so dissection of extant taxa alone is inadequate for modeling xenacanth musculature.Support or Funding InformationRichard Gilder Graduate School at the American Museum of Natural HistoryThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.
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