Figure 4.

Phylogenetic distribution of reconstructed diel activity patterns in non-mammalian synapsids. Our results suggest that fossil synapsids displayed the full range of diel activity patterns. Maximum-likelihood and Bayesian estimates of ancestral states (see the electronic supplementary material for details) indicate synapsids were nocturnal ancestrally, even though further sampling is required to make more formal assessments. Our results also suggest that foraging ecology is linked with diel activity patterns. Small herbivores tend to be diurnal, whereas carnivores are predominantly nocturnal or cathemeral. It is important to account for this complexity when discussing the evolution of diel activity patterns in mammals. Numbers denote the following major synapsid clades: 1 = Varanopidae, 2 = Sphenacodontidae, 3 = Biarmosuchia, 4 = Gorgonopsia, 5 = Anomodontia, 6 = Therocephalia. Titanophoneus potens is a member of Dinocephalia, and Tritylodon longaevus is a member of Cynodontia. Timescale after [27].