The aquaticLystrosaurus:An alternative lifestyle

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Abstract
Certain distinctive features of the skull and postcranial skeleton of Lystrosaurus are discussed. The mechanics of the skull are re‐evaluated and it is concluded that the skull was modified relative to Permian forms to produce a bigger bite force and more vertical component of the adductor muscles, while preserving a wide gape. A zone of weakness, acting as a shock absorption system, was present in the premaxillary‐nasal region of the skull. Antero‐posterior movement of the lower jaw had been reduced. It is concluded that the skull was used to crush resistant plant matter. The external nasal opening presents no evidence for a valvular structure, but may have housed a nasal gland. The flared scapula produced a slightly greater mechanical advantage in the limb protractors and retractors. The manus was short and broad, suitable for digging, but the claws were flat and rounded. The wide knee‐joint indicated powerful foot‐moving muscles. The palaeoenvironment of the Lystrosaurus‐Thrinaxodon Assemblage Zone is examined. It was probably drier than usually described. The fauna contained many terrestrial elements. Lystrosaurus was probably a fully terrestrial animal which may have excavated burrows for itself, but was not a committed burrower like Cistecephalus.

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