CRUNCHY ON THE OUTSIDE, CHEWY ON THE INSIDE: EVIDENCE FOR VERTEBRATE PREDATION AND RECOVERY IN THE MISSISSIPPIAN BLASTOID PENTREMITES SPICATUS

Predation is a major selective pressure, driving evolutionary patterns throughout metazoan evolution, and yet, it is a topic that must often be approached indirectly in the fossil record. Predation is, by definition, a destructive process for the prey item, and trace fossils recording incidents of trophic interactions often represent modifications of discarded prey portions or partially healed injuries on survivors of failed attacks. These feeding traces offer rare snapshots into the paleobiology of both predator and prey groups. Boreholes and partially lost or regenerated arms are the most commonly preserved evidence of predation upon stalked echinoderms. Here we present evidence of vertebrate predation on the thecae of Pentremites spicatus, a Mississippian (Chesterian) blastoid from the Pennington Formation of White County, Tennessee. These partially healed feeding traces preserve evidence of associated impact-related damage and subsequent healing, indicating that these animals survived these predation attempts. Individual tooth marks are roughly fusiform in shape, indicating that the predator exhibited laterally compressed teeth, a feature shared by many fish groups that coexisted alongside Pentremites spicatus. The healing process has overwritten any more diagnostic features of the bite marks (e.g. serrations, etc.) making more specific identification impossible. Damage and regeneration of a portion of an ambulacrum removed a section of brachioles and lateral food grooves reducing the food capture potential of the blastoids post attack. However, these same patterns of regeneration and reaction tissue indicate that the blastoids’ respiratory structures, while damaged and deformed by the attacks, were still functioning. Computed tomographic imaging of conspecifics reveals unusually well-preserved and observable respiratory structures in these fossils. Future scanning will focus on the pathological specimens to reveal how these structures, which rely on water currents passively generated by overall theca morphology, responded and recovered from significant surficial crushing and indentation.