preceded oral processing in the evolution of caseid herbivory. A juvenile insectivorous diet would have provided the opportunity for successful introduction into the intestine of microorganisms capable of endosymbiotic cellulolysis, particularly if the prey ingested were herbivorous insects which harbor such microorganisms in their viscera. Subsequently, the caseids adopted a strictly herbivorous diet and evolved into gigantic forms. These herbivorous caseids had spatulate teeth equipped with more or less numerous cuspules and a very enlarged and barrel-shaped rib cage which must have housed highly developed intestines necessary for the digestion of plants with low nutritional value. This adaptation would partly explain the diversification and expansion of the group at the end of the Lower Permian and during the Middle Permian, because it allowed them to exploit a fiber-rich plant resource that had by then become abundant and widespread. Nevertheless, small probably faunivorous caseids like Phreatophasma seem to have persisted until the Middle Permian. Semiaquatic vs terrestrial lifestyle Caseids are generally considered primarily terrestrial animals. Everett C. Olson in particular considered that the degree of ossification of the skeleton, the relatively short feet and hands, the massive claws, the limbs with very powerful extensor muscles, and the solid sacrum, strongly suggested a terrestrial lifestyle. Olson did not rule out that the caseids spent some time in water, but he considered locomotion on land to be an important aspect of their lifestyle. It has been suggested that the very powerful forelimbs, with strong and very tendinous extensor muscles, as well as very massive claws, could be used to dig up roots or tubers. However, the very short neck implied a low amplitude of vertical movements of the head which precluded the large species from feeding at ground level. Another hypothesis suggests that the caseids could have used their powerful forelimbs to fold large plants towards them, which they would have torn off with their powerful claws. Other hypotheses suggest that some caseids such as Cotylorhynchus used their limbs with powerful claws to defend themselves against predators, or during intraspecific activities linked in particular to reproduction. According to Olson, an interesting thing about this, is that almost all known specimens of the species Cotylorhynchus hancocki have one to ten ribs broken and healed during life. Finally, for some authors, the large derived caseids would have been semiaquatic animals that used their hands with large claws like paddles, which could also be used to