Multivariate complexity analysis of 3D surface form and function of centric diatoms at the Eocene-Oligocene transition

- Centric diatom complexity is a multivariate quantity.
- Centric diatom complexity increases across the Eocene-Oligocene transition.
- Complexity as an evolutionary trend is weakly directional for centric diatoms across the Eocene-Oligocene transition.
- Functional complexity increases as predation resistance across the Eocene-Olicogene transition for centric diatoms.

Complexity is important in the course of evolution, but consensus of what complexity analysis entails is elusive. In this study, multivariate complexity is measured and analyzed in terms of magnitude of change and the trends behind those changes. Multivariate morphological and functional complexities were analyzed using 3D surface models of centric diatom genera from the Eocene to Oligocene, a transitional time when temperatures cooled, sea levels rose, and glaciation increased. Diatoms were chosen for study because of their importance in biostratigraphy, biogeochemical cycling, productivity, food web dynamics, and sensitivity to environmental conditions. Probabilistic analysis using a Markov chain indicated an increase in total complexity across the Eocene-Oligocene transition (EOT). Causal inference via structural equation modeling indicated weakly driven functional and morphological complexity trends over the EOT. Morphological and functional complexity trends differed with respect to predation resistance as responses to ecological complexity as environmental and climate change occurred across the EOT. Macroevolutionary patterns of morphological and functional complexity with respect to ecological complexity did not necessarily coincide over time.

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