Fig. 3.

Eye socket lengths across the taxa in Fig. 2 grouped by the regime shift analysis. (A) The mean (horizontal bars) absolute eye socket length of digited tetrapods was three times larger than that of their finned relatives, with the elpistostegalians (finned-transitional) midway. The digited tetrapods that returned to life underwater (adelospondyl-colosteids, digited-aquatic) reverted to a size similar to that of their finned relatives. (B) Relative eye socket size was calculated as residuals from a phylogenetically informed regression of log₁₀-transformed variables (Materials and Methods) averaged over the full set of 1,000 trees. Positive residuals indicate eye sockets larger than expected based on skull length, whereas negative residuals indicate eye sockets smaller than expected. The Bayesian OU results in Fig. 2 show the presence of an adaptive evolutionary process and provide estimates of the adaptive peak for each group (horizontal bars). The elpistostegalians entered a new selective regime but are lagging behind, because time was insufficient to accrue enough increases in eye socket size to reach the peak.However, the digited tetrapods are centered around their adaptive peak, except for the adelospondyl-colosteids. As expected for adiverse group, not all tetrapods are at their respective peak, reflecting a normal evolutionary pattern in which trait values are dispersed around the optimal value. The Bayesian OU findings show that there must have been a selective benefit from larger eye sockets in finned transitional and digited tetrapods, but uncovering its basis requires modeling visual performance across likely environments.