PUTTING MODELS TO THE TEST: ASSESSING THE ADEQUACY OF MORPHOLOGICAL MODELS USED IN PALAEOBIOLOGY (Invited Presentation)

Phylogenetic trees allow us to reconstruct the evolutionary history of organisms, offering valuable insights into how life originated and diversified on Earth. Given that most organisms are now extinct, incorporating fossils into phylogenetic analyses is vital to further our understanding of evolution in deep time. To do this in a Bayesian phylogenetic framework, we require a substitution model that describes the morphological evolution of both extinct and extant taxa. Developing such a model has posed significant challenges, making the Mk Lewis model the most commonly used. Despite its widespread application in paleobiology, it is not known whether the simple Mk substitution model, or any extensions to it, provide a sufficiently good description of the process of morphological evolution. Here, using a wide range of empirical data sets, I demonstrate how different morphological models have significant impacts on key parameter estimates, illustrating the importance of model choice. Following this, I present a pipeline for assessing adequacy (or absolute fit) of available substitution models using posterior predictive simulations. This approach enables us to assess whether a given data set could have been plausibly generated under the assumptions of our model. When applied to empirical data, I found that current variations of the Mk model often perform adequately, in terms of capturing the evolutionary dynamics that generated our data. There was no discernible preference for a particular model extension across multiple data sets, indicating that there is no ‘one size fits all’ when it comes to morphological data and that careful consideration should be given to choosing models of discrete character evolution. Further, using an exemplar data set of Cambrian echinoderms, I demonstrate the impact the morphological model has on divergence time estimates when applying the fossilized birth-death model. By using suitable models of character evolution, we can increase our confidence in our phylogenetic estimates, which in turn allows us to gain more accurate insights into the evolutionary history of both extinct and extant taxa.