Origins and early evolution of herbivory in tetrapods.

The first herbivorous tetrapods date from the Late Carboniferous, about 300 million years ago. By the Late Permian, continental ecosystems of `modern' aspect had been established, with a vast standing crop of herbivores supporting relatively few carnivores. Processing of high-fibre plant material requires (1) structural modifications of the dentition, jaw apparatus and digestive tract and (2) the acquisition of microbial endosymbionts that produce the enzymes needed for fermentative digestion of cellulose, the principal compound of cell walls in plants. Recent phylogenetic analyses of tetrapods indicate that endosymbiotic cellulysis was acquired independently in a number of lineages during the late Palaeozoic.