Earliest direct evidence of trophic interactions between terrestrial apex predators and large herbivores

Trophic interactions between large predators and herbivores are unknown in the fossil record of Permo-Carboniferous tetrapods at a time when these members of the terrestrial vertebrate communities make their first appearance and undergo initial diversification in an increasingly complex community. Here we report on the presence of numerous tooth markings on three juvenile skeletons of the herbivore Diadectes from the early Permian of Texas. As the first terrestrial vertebrate herbivores, diadectids occupied a crucial eco-morphological space of the terrestrial community, as primary consumers that were able to orally process and consume high-fiber plants, a previously unexplored resource. The tooth marks indicate that the feeding behaviour included both muscle de-fleshing and scavenging on cartilage-rich joint areas in the appendicular skeletons. Anatomy of the tooth marks indicate that various predators could have produced the tooth marks, such as the apex predators Varanops and Dimetrodon, as well as the trematopid amphibian Acheloma. In addition, boring marks are also present and likely produced by arthropod larvae. Although these skeletons may have been produced by active predation, their subsequent accumulation in a probable flooding event and extensive exposure before burial, does not allow us to differentiate active predation and scavenging. Nevertheless, this discovery represents the earliest direct evidence of predator-prey trophic interactions among large-bodied terrestrial vertebrates during the initial stages of amniote evolution.