PhD: Mass Extinction and Recovery of Marine Vertebrates Across the K-Pg boundary

INTRODUCTION

The K-Pg mass extinction wiped out up to 90% of all species on Earth (1), devastating Cretaceous ecosystems and leading to the origin of the species that dominate the planet today. Following the impact of the giant Chicxulub asteroid, soot and dust launched into the high atmosphere blocked out sunlight, suppressing photosynthesis and leading to a collapse of the food chain (2). The effects of the extinction have been extensively studied in terrestrial ecosystems, where the end of the Cretaceous saw the demise of the dinosaurs, along with devastating extinctions of birds (3), mammals (1), and lizards (4), followed by the evolution of a new ecosystem dominated by mammals. Less attention has been paid to marine vertebrates, however, despite the fact that they have a highly complete fossil record.

PROJECT AIMS AND METHODS

A new fossil collection from the late Maastrichtian and early Paleogene of Morocco, north Africa, provides an unparalleled view of this transition, providing new information on the mosasaurs, plesiosaurs, turtles, crocodiles, fish, and sharks across the K-Pg boundary. This collection will form a major focus of a project examining the K-Pg extinction. Questions to be addressed include:

1) How severe was the extinction? Has the Signor-Lipps effect obscured the severity of the extinction, with groups that apparently went extinct earlier in the Cretaceous actually persisting up to the K-Pg boundary?

2) How rapid was the recovery? How long did it take for the Cenozoic marine fauna to reach peak diversity?

3) How did the recovery fauna- dominated by groups such as giant palaeophiid sea snakes, dyrosaurid and gavialoid crocodylians- give way to the modern marine fauna?

The project will focus on both classic descriptive paleontology, describing and naming new species and assessing their relationships, and quantitative approaches to describing diversity, including morphometrics, character-based approaches to disparity, and functional diversity. For the descriptive part of this project, we have a diverse fauna of marine turtles, including numerous new species, from the late Maastrichtian and early Paleogene, which would form an ideal focus for a study. For the quantitative part of the project, the student will develop a database of marine vertebrates including variables such as body size, feeding mode, locomotor mode, and habitat to understand changes in ecological niche occupation (functional diversity), including changes in ecological niche occupation across the K-Pg boundary, recovery in the Cenozoic, and the effects of environmental change in the Cenozoic.