CHANGES IN CHONDRICHTHYAN TOOTH NICHE SPACE ACROSS THE PERMIAN-TRIASSIC BOUNDARY

The boundary between the Permian and Triassic Periods represents the most severe global extinction event to have occurred during the Phanerozoic Eon. This extinction event led to the loss of an estimated 70% of land-based species and over 90% of marine species, and paved the way for the appearance of new groups in the Mesozoic and Cenozoic Eras. Chondrichthyans (sharks, rays, and chimaeras) have their evolutionary origins in the Early and Middle Paleozoic Era, and many chondrichthyan groups such as the Xenacanthimorpha, Hybodontiformes, and Neoselachii survived the End-Permian extinction and persisted well into (or beyond) the Triassic. While taxonomic diversity has been increasingly studied across this extinction boundary, less is known regarding the disparity of functional niches occupied by chondrichthyans before and after this extinction event. We used landmark-based morphometrics to examine the variance in tooth morphology among bransonelliform, xenacanthiform, hybodontiform, and other euselachian genera from lineages in the Late Permian Period and Early Triassic Period, and from lineages that occur in both periods. Relative differences in tooth morphology were investigated using multivariate ordination of Procrustes tooth space from 20 taxa to construct a general niche space for tooth shape. Preliminary results indicate a slight decline in morphological diversity moving across this boundary. This current pilot study suggests that chondrichthyan teeth began to display greater morphological variation despite a relative drop in taxonomic diversity during the Late Permian and Early Triassic. More data are essential and will be collected to further elucidate these ecological trends, and provide a better ecological framework for chondrichthyan turnover across this boundary.