A rapid burst in the diversification of animals and their disparity of body forms – the Cambrian explosion – began over 500 million years ago. Exceptional fossil deposits from this time that preserve soft tissues provide critical data for resolving the origins and evolutionary trajectories of modern groups. Arthropoda, which includes modern crabs, millipedes, and insects, is the most diverse phylum today. Arthropods have been abundant and important members of animal ecosystems since their origin and radiation over 500 million years ago, dramatically changing the functioning of the biosphere.
I address questions relating to the evolutionary relationships, ecology, and range of forms of early arthropods, using fossil material. Underpinning my research is a desire to understand how past animals lived, why particular morphologies evolved, and test hypotheses linking form and function in extinct groups. Furthermore, as arthropods are so important in modern ecosystems and for Earth systems such as the biological pump, I explore the impact of arthropod innovations on the development of these systems over 500 million years ago.
Three central themes to my current research are:
A global understanding of arthropod diversity
Famous fossil sites such as the Burgess Shale in Canada and Chengjiang in China provide exceptional insights into the anatomy, diversity and evolution of early animals. However, because they are located at one point in time and place, they cannot tell us everything. For example, do we have different species at these sites because of their geographic distance, differences in time, or both?
I have worked on material from the Burgess Shale and Chengjiang, alongside less studied - though I would argue no less exceptional - fossil material from deposits in Canada, China, Morocco, Spain, UK and USA in order to build a global picture of arthropod diversity. Exploring a broader range of fossil localities - spanning a range of ages and geographic locations - allows temporal and geographic signals to be unravelled. Furthermore, these sites reveal new taxa not known from the more studied fossil deposits.
New taxa that I have described from these relatively untapped deposits include Opabinia's sister, Utaurora , the tiny Welsh 'bramble-snout' Mieridduryn and the fearsome hurdiid radiodont Buccaspinea. In addition, my work has revealed the first radiodonts from Spain and Wales.
Descriptions of new taxa not only increase our knowledge of arthropod diversity, geographic ranges, and feeding modes, but they also add critical data for furthering our understanding of internal arthropod relationships, and how the arthropod body plan evolved.
Linking form and function in extinct animals
I use statistical methods, and combine morphometric analyses with engineering-based simulations to quantitatively test hypotheses linking form and function in extinct arthropods.
I have demonstrated the role of elongated spines in some Cambrian trilobites as predatory deterrents, and importance of carapace shape in the cosmopolitan arthropod Isoxys for streamlining and lift generation.
For my current research project, I am testing the hydrodynamic importance of trilobite heads (cephala) for facilitating different life modes. To do this, I am constructing a dataset of 3D trilobite models, to quantify variation within the group. I will then use these data to address questions relating to evolutionary convergence between trilobites and other distantly related arthropods.
Bumastus trilobite model, constructed using photogrammetry.
Eoharpes trilobite with malformed fringe. The function of the harpetid fringe is still open to much debate.
Arthropods were involved at many trophic levels and water depths in Cambrian oceans - playing an important role in the early Palaeozoic biosphere.
Laminar flow around a 2D model of an Isoxys carapace.
Arthropods and the biosphere
Arthropods dominate zooplankton biomass, and are critical members of modern ecosystems and Earth systems. The evolution of arthropods changed how ecosystems and the biosphere worked.
In the Cambrian, arthropods such as radiodonts were important large predators, but also occupied other vital ecological roles including filter feeders. Radiodonts were active at a range of depths in the water column.
By quantifying the hydrodynamic performance of Isoxys carapaces, I was able to show that some members of the genus performed similarly to modern arthropods which are vertically mobile in the ocean. This demonstrated that some Cambrian arthropods were likely actively transporting nutrients vertically in the ocean, helping to ventilate the ocean and fuel deeper water communities over 500 million years ago.