Abstract
Evidence previously cited for the aquatic nature of the Triassic mammal‐like reptile Lystrosaurus is reviewed. It is concluded that this evidence does not constitute a convincing case. General adaptations of aquatic tetrapods are reviewed and applied to the morphology of Lystrosaurus, in order to determine whether aquatic adaptations not previously sought in Lystrosaurus are present It is concluded that few or any such adaptations are present. Such as are, for example a widened knee and flared scapula blade, are as compatible with a digging function, as with swimming. Nevertheless, the distinctive nature of the skull and to a lesser extent the postcranial skeleton of Lystrosaurus stands out, and several features require functional interpretation. These include: a downwardly‐directed and elongated snout, a short and high temporal region, a pear‐shaped external nasal opening bounded by a rugose ridge, slight dorsal flaring of the scapula, a powerful forelimb and wide knee joint These are dealt with elsewhere (King and Cluver, 1991).

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