Diet Evolution and Body Temperature in Tetrapods: Cool Old Carnivores and Hot Young Herbivores.

Aim: Diet is a key aspect of life in animals. There have been numerous independent origins of herbivorous diet across animals, but the factors that explain these origins remain poorly understood. One potentially crucial factor is body temperature (Tb), as the gut‐dwelling bacteria that help digest cellulose in many herbivores are thought to require high temperatures. However, analyses in birds, lizards and mammals found only limited evidence for higher Tb in herbivores than in carnivores. These analyses tested whether diet explains Tb evolution. Here, we focus instead on testing whether Tb helps explain the evolution of diet across tetrapods. Location: Global. Time Period: Past 350 million years. Major Taxa Studied: Tetrapods. Methods: We analysed 1712 species with matched data on diet and Tb using diverse phylogenetic methods. Results: Ancestral reconstructions indicated that tetrapods likely had a carnivorous ancestor, followed by repeated transitions to omnivory and herbivory, especially in the last 110 million years. Thus, extant herbivorous lineages in tetrapods are relatively young, in contrast to many older carnivorous lineages. They are also relatively unstable in that reversals from herbivory back to omnivory and from omnivory back to carnivory were as frequent as the origins of herbivory and omnivory. Using phylogenetic logistic regression, we support the hypothesis that higher Tb helps explain the evolution of herbivory across tetrapods and within birds, mammals, lepidosaurs and turtles. Phylogenetic path analyses suggest that Tb generally drives the evolution of herbivory, and not vice versa. Our analyses also suggest that Tb is more important for the evolution of herbivory than large body size or diurnal diel activity, which are both significant predictors of herbivory in some cases. Main Conclusions: Our results show for the first time that Tb is a significant predictor of diet evolution among and within many major animal clades. [ABSTRACT FROM AUTHOR]