Predation in the Cambrian

Thesis

Although predation has been suggested repeatedly as a force shaping the diversification of animals during the Cambrian period, studies of the evolutionary dynamics of predation are lacking from this time period. Radiodonta, the largest Cambrian nektonic animals, and repaired injuries on trilobites, a diverse and disparate group of prey animals, provide study systems to assess predation dynamics at this time. Radiodont fossils were first discovered over 100 years ago, but are now known worldwide from early Palaeozoic deposits which preserve soft-bodied material. Intense research on radiodonts from the Chengjiang biota (China) and Burgess Shale (Canada) since 2009 recently greatly improved our knowledge of the group, outdating previous interpretations of USA specimens, which are needed for large-scale analyses. Anecdotal reports of repaired injuries on trilobites are common in the literature, but quantitative studies on the role of morphology, behaviour, or geography have not been conducted.

I restudied radiodonts from the USA, placed them into an up to date taxonomic and taphonomic context, and revealed that these deposits hold a much higher diversity and disparity than previously reported. Findings include the first and last appearances of a number of families worldwide, and eight taxa not known from any other deposit. I used this new data to undertake the most comprehensive phylogenetic analysis and the first diversity and disparity analyses of Radiodonta, which showed two phases of evolution in the group, and that the ancestral radiodont was likely not a raptorial predator. I also performed the first quantitative measurements of predation pressure on trilobites, showing that morphology, geography, and behaviour, effect on the location and frequency of repaired injuries. These results suggest that predation pressure was a complex and changeable ecological influencing the early evolution of animals.

Authors: Pates, S

• DOI: 10.5287/ora-8gbkjkryd
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford