Testing the roles of extratropical origination and predation on irregular echinoid evolution
Miller, Justin Matthew
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The number of extratropical vs. tropical originations and the predation frequency of fossil irregular echinoids were analyzed to gain a better understanding of their evolution. The latitudinal diversity gradient for irregular echinoids is atypical compared to other marine bivalves and current evolutionary models are not applicable. An out-of-the-extratropics (OTE) model is used to describe how marine organisms may originate in the extratropics and then migrate into tropical regions. Irregular echinoids from the Late Eocene Ocala Limestone were categorized into burrow tiers based on morphological characters so predation frequency at different burrow depths could be assessed. Predation frequency was highest for medium and deep burrow tiers, suggesting that burrowing does not reduce cassid predation. This may indicate that evolution towards infaunalism for irregular echinoids was not driven by increasing predation pressure in the Mesozoic.