CONODONT BODY SIZE AND DIVERSITY TRENDS AFTER THE END-PERMIAN EXTINCTION: IMPLICATIONS FOR THE RECOVERY OF PELAGIC VS. BENTHIC MARINE ECOSYSTEMS

Many marine clades decreased in size across the end-Permian extinction horizon, but the pattern and timing of subsequent size increase during recovery is poorly constrained. The tempo of recovery from the end-Permian extinction is key to understanding the role of evolutionary and environmental constraints in the recovery of ecosystems. However, not all marine organisms share the same recovery pattern. In this study, we document Late Permian to Late Triassic trends in size distribution of conodonts, pelagic chordates that exhibit much more rapid diversification in the Early Triassic compared to benthic clades. Because tooth size correlates with body weight in chordates over many orders of magnitude and is commonly used to predict body size in fossils, conodont elements can serve as a proxy for the size of the conodont animal. Our dataset includes both specimens from high-resolution samples through an exceptionally exposed carbonate platform in south China and size measurements from the published literature for conodonts and seven other marine clades. In platform slope sections of south China, we observe a size decrease across the P/Tr boundary, but in platform interior sections, large conodonts are prolific in the earliest Triassic. Comparison with global data shows that while there is decrease in median conodont size across the P/Tr boundary, there is little change in maximum conodont size, and pre-extinction size distributions return by the Smithian. While benthic clades show Early Triassic size reduction and slow recovery, pelagic clades such as conodonts and ammonoids show large size and rapid diversification after the extinction event. This decoupling of recovery between benthic and pelagic marine ecosystems could reflect a depth gradient in environmental parameters such as oxygen availability or intrinsic differences in the evolutionary dynamics of these clades.