No state change in pelagic fish production and biodiversity during the Eocene-Oligocene Transition

The Eocene-Oligocene (E/O) boundary ~33.9 million years ago, has been
described as a state change in the Earth system marked by the
permanent glaciation of Antarctica and a proposed increase in oceanic
productivity. Here we quantified the response of fish production and
biodiversity to this event using microfossil fish teeth
(ichthyoliths) in seven deep-sea sediment cores from around the
world. Ichthyolith accumulation rate (a proxy for fish biomass
production) shows no synchronous trends across the E/O. Ichthyolith
accumulation in the Southern Ocean and Pacific Gyre sites is an order
of magnitude lower than the equatorial and Atlantic sites,
demonstrating that the Southern Ocean was not a highly productive
ecosystem for fish before or after the E/O. Further, tooth morphotype
diversity and assemblage composition remained stable across the
interval, indicating little change in the biodiversity or ecological
role of open ocean fish. While the E/O boundary was a major global
climate change event, its impact on pelagic fish was relatively
muted. Our results support recent findings of whale and krill
diversification which suggest that the pelagic ecosystem
restructuring commonly attributed to the E/O transition likely
occurred much later, in the late Oligocene or Miocene.