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Molecular phylogenies suggest some major radiations of open-ocean fish clades occurred roughly coincident with the Cretaceous-Palaeogene (K/Pg) boundary, however the timing and nature of this diversification is poorly constrained. Here, we investigate evolutionary patterns in ray-finned fishes across the K/Pg mass extinction 66 million years ago (Ma), using microfossils (isolated teeth) preserved in a South Pacific sediment core spanning 72-43 Ma. Our record does not show significant turnover of fish tooth morphotypes at the K/Pg boundary: only two of 48 Cretaceous tooth morphotypes disappear at the event in the South Pacific, a rate no different from background extinction. Capture-mark-recapture analysis finds two pulses of origination in fish tooth morphotypes following the mass extinction. The first pulse, at approximately 64 Ma, included short-lived teeth, as well as forms that contribute to an expansion into novel morphospace. A second pulse, centred at approximately 58 Ma, produced morphotype novelty in a different region of morphospace from the first pulse, and contributed significantly to Eocene tooth morphospace occupation. There was no significant increase in origination rates or expansion into novel morphospace during the early or middle Eocene, despite a near 10-fold increase in tooth abundance during that interval. Our results suggest that while the K/Pg event had a minor impact on fish diversity in terms of extinction, the removal of the few dominant Cretaceous morphotypes triggered a sequence of origination events allowing fishes to rapidly diversify morphologically, setting the stage for exceptional levels of ray-finned fish diversity in the Cenozoic.

Ichthyoliths, isolated fossil fish teeth and shark dermal scales preserved in deep-sea sediment cores, can reveal how marine vertebrate consumers (sharks and fish) have responded to major global change events in Earth’s history. In this dissertation, I first develop methods for the isolation and curation of ichthyoliths from a variety of marine sediment types. I then use ichthyoliths to assess how (1) total fish production, (2) pelagic fish community structure, and (3) fish evolution have responded to select global change events in Earth’s history. The Cretaceous/Paleogene (K/Pg) Mass Extinction 66 million years ago (Ma) catalyzed the diversification of fish in the open ocean. Cretaceous oceans (>66 Ma) were relatively devoid of fish teeth, and at the K/Pg, fish abundance declined only in the Atlantic Ocean, while in the Pacific, fish abundance stayed constant or increased immediately following the extinction. Yet the event caused a global shift in the marine vertebrate community, with the relative abundance of teeth increasing compared to that of denticles in marine sediments. Further, the size structure of the fish tooth assemblages shifted towards larger, rather than smaller individuals, suggesting that the group was resilient to the extinction event. Bony fishes rose to ecological dominance in the open ocean following the K/Pg extinction, rapidly radiating in morphological diversity after the extinction, while other open ocean groups lagged behind. Extreme global warmth in the Early Eocene (~52-48 Ma) is associated with an increase in fish and shark abundance, but not diversity. Fish abundance broadly follows global temperature gradients in the Paleogene (66-20 Ma), with the highest abundance of fish in the warmest part of the Cenozoic. The most recent 20 million years is characterized by highly variable ichthyolith production and low abundances of sharks and other elasmobranchs in the gyres. This shift is temporally correlated with the diversification of ope

The Eocene-Oligocene Transition (EOT) from 35-33 Ma, centered at 33.9 million years ago (Ma), marks the transition from a Greenhouse to an Icehouse earth. It is associated with the appearance of bulk-feeding whales, and the widespread increase in opal sedimentation in the earliest Oligocene, and has been interpreted to record the initiation of a highly productive Southern Ocean ecosystem. We measured accumulation rates of pelagic fish teeth and shark denticles (ichthyoliths) in a global array of ocean cores that span the EOT to test the impact of this transition on mid-level pelagic consumers, which could serve as trophic links between the opal-producing diatoms and larger, predatory whales. We find that there is no increase in fish productivity across the Eocene Oligocene Transition in any of our records; indeed, few records show any changes in fish production associated directly with the E/O boundary or the Oi-1 glaciation event at 34 Ma. Moreover, we find that export productivity was lower in our Southern Ocean sites compared to lower latitude sites in both the Atlantic and tropical Pacific for the duration of the records. Ecosystem models predict that diatom-based food webs should support abundant top predators. However, with reduced fish productivity, we speculate that diatoms instead formed the base of a food web which short-circuited fishes, perhaps feeding krill and other seasonally blooming zooplankton that in turn directly supported seasonally present top predators such as large whales.

Ichthyoliths, isolated fossil fish teeth and shark dermal scales preserved in deep-sea sediment cores, can reveal how marine vertebrate consumers (sharks and fish) have responded to major global change events in Earth’s history. In this dissertation, I first develop methods for the isolation and curation of ichthyoliths from a variety of marine sediment types. I then use ichthyoliths to assess how (1) total fish production, (2) pelagic fish community structure, and (3) fish evolution have responded to select global change events in Earth’s history. The Cretaceous/Paleogene (K/Pg) Mass Extinction 66 million years ago (Ma) catalyzed the diversification of fish in the open ocean. Cretaceous oceans (>66 Ma) were relatively devoid of fish teeth, and at the K/Pg, fish abundance declined only in the Atlantic Ocean, while in the Pacific, fish abundance stayed constant or increased immediately following the extinction. Yet the event caused a global shift in the marine vertebrate community, with the relative abundance of teeth increasing compared to that of denticles in marine sediments. Further, the size structure of the fish tooth assemblages shifted towards larger, rather than smaller individuals, suggesting that the group was resilient to the extinction event. Bony fishes rose to ecological dominance in the open ocean following the K/Pg extinction, rapidly radiating in morphological diversity after the extinction, while other open ocean groups lagged behind. Extreme global warmth in the Early Eocene (~52-48 Ma) is associated with an increase in fish and shark abundance, but not diversity. Fish abundance broadly follows global temperature gradients in the Paleogene (66-20 Ma), with the highest abundance of fish in the warmest part of the Cenozoic. The most recent 20 million years is characterized by highly variable ichthyolith production and low abundances of sharks and other elasmobranchs in the gyres. This shift is temporally correlated with the diversification of ope

The Eocene-Oligocene Transition (EOT) from 35-33 Ma, centered at 33.9 million years ago (Ma), marks the transition from a Greenhouse to an Icehouse earth. It is associated with the appearance of bulk-feeding whales, and the widespread increase in opal sedimentation in the earliest Oligocene, and has been interpreted to record the initiation of a highly productive Southern Ocean ecosystem. We measured accumulation rates of pelagic fish teeth and shark denticles (ichthyoliths) in a global array of ocean cores that span the EOT to test the impact of this transition on mid-level pelagic consumers, which could serve as trophic links between the opal-producing diatoms and larger, predatory whales. We find that there is no increase in fish productivity across the Eocene Oligocene Transition in any of our records; indeed, few records show any changes in fish production associated directly with the E/O boundary or the Oi-1 glaciation event at 34 Ma. Moreover, we find that export productivity was lower in our Southern Ocean sites compared to lower latitude sites in both the Atlantic and tropical Pacific for the duration of the records. Ecosystem models predict that diatom-based food webs should support abundant top predators. However, with reduced fish productivity, we speculate that diatoms instead formed the base of a food web which short-circuited fishes, perhaps feeding krill and other seasonally blooming zooplankton that in turn directly supported seasonally present top predators such as large whales.

Ray-finned fishes (Actinopterygii) comprise nearly half of all modern vertebrate diversity, and are an ecologically and numerically dominant megafauna in most aquatic environments. Crown teleost fishes diversified relatively recently, during the Late Cretaceous and early Paleogene, although the exact timing and cause of their radiation and rise to ecological dominance is poorly constrained. Here we use microfossil teeth and shark dermal scales (ichthyoliths) preserved in deep-sea sediments to study the changes in the pelagic fish community in the latest Cretaceous and early Paleogene. We find that the Cretaceous-Paleogene (K/Pg) extinction event marked a profound change in the structure of ichthyolith communities around the globe: Whereas shark denticles outnumber ray-finned fish teeth in Cretaceous deep-sea sediments around the world, there is a dramatic increase in the proportion of ray-finned fish teeth to shark denticles in the Paleocene. There is also an increase in size and numerical abundance of ray-finned fish teeth at the boundary. These changes are sustained through at least the first 24 million years of the Cenozoic. This new fish community structure began at the K/Pg mass extinction, suggesting the extinction event played an important role in initiating the modern "age of fishes."