Meeting Abstract
The Cretaceous-Paleogene (K/Pg) mass extinction profoundly disrupted marine ecosystems. However, there is mounting genetic and fossil evidence that marine fishes thrived in the aftermath of the extinction event, diversifying rapidly in the early Paleogene open ocean. Here we use ichthyoliths – microfossil fish teeth – preserved deep-sea sediments from the South Pacific Ocean (DSDP Site 596) to investigate the structure of open ocean fish communities from the Cretaceous to the middle Eocene (72-43 Ma). We find that there were two pulses of elevated origination rate of fish tooth morphotypes during the Paleocene. These pulses, which occurred at 64 Ma and from 60-55 Ma respectively, expanded into distinct regions of tooth morphospace, representing differential responses of fish to the mass extinction event. Dissimilarity analyses of fish tooth assemblages reveal that the Cretaceous, and Eocene had distinct but stable fish community structures, which were linked by a v-shaped trajectory through NMDS-space during the Paleocene. The inflection point of this trajectory occurred between the two pulses of origination in the Paleocene. We then used clustering algorithms to group tooth morphotypes with similar shapes, creating morphotype clusters recognized across time bins, and repeated the dissimilarity analyses. The observed pattern of fish community evolution remains consistent across a wide range of morphotype cluster numbers and clustering algorithms, suggesting that there were fundamental shifts in the composition and structure of fish communities across the K/Pg and during the Paleocene. These results suggest that there were distinct shifts in the role that fish played within the Paleocene marine ecosystem, both individually and as an ecological group, as they diversified in the early Cenozoic.
