Meeting Abstract

45-9   15:30 - 15:45  Trends in the evolution of the tetrapod jaw Watt, EC*; Goswami, A; Felice, RN; Natural History Museum, London, UK and University College London, UK; Natural History Museum, London, UK; University College London, UK emily.watt1@nhm.ac.uk

Tetrapods (limbed vertebrates) have undergone considerable evolutionary changes during and since their initial water-to-land transition around 390Ma. Following this major ecological shift, there was a surge in morphological diversity due to expansion into unexplored terrestrial niches. This included acquisition of a breadth of morphological adaptations for new diets and foraging strategies. Here, we reconstruct morphological evolution of the tetrapod mandible to identify trends in number of elements (i.e. Williston’s Law) and shifts in disparity through time, potentially related to large-scale events (e.g. mass extinctions). We recorded 36 discrete and meristic lower jaw characters across 117 fossil and 29 extant tetrapods from published literature. We focussed on the early tetrapod and amphibian clades and included temnospondyls, lepospondyls, and a few tetrapodomorphs and stem-amniotes. We created a composite phylogeny, performed disparity through time and principal coordinates (PCoA) analyses and tested macroevolutionary tempo and mode of tooth count and mandible complexity (number of elements). PCoA indicated that jaw morphology is largely influenced by phylogeny along PCO1, which represents the majority of variation (60.8%) in the dataset. Jaw disparity generally increases through time, with the most rapid increase observed since the end of the Eocene. Interestingly, there was no increase in diversity associated with the initial expansion onto land nor were large shifts associated with major mass extinction events, except for a small increase after the end-Cretaceous event. We found the most supported models were an overall trend towards reduced tooth count and an early burst of mandibular complexity. Our results demonstrate that the lower jaw has undergone substantial morphological and structural change across tetrapod evolution, but different aspects of jaw morphology show distinct evolutionary patterns.