A revision of the early Triassic “capitosaurs” (Stegocephali, Stereospondyli) from Madagascar, with remarks on their comparative ontogeny

ABSTRACT

The “capitosaurs” from the Lower Triassic of Madagascar are revised. Benthosuchus madagascariensis Lehman, 1961, and Wetlugasurus milloti Lehman, 1961, are combined in the new combination Watsonisuchus madagascariensis on the basis of the most complete growth series among capitosaurians. A phylogenetic analysis showed that the genus Watsonisuchus is justified, although its species W. madagascariensis is not the most derived within the genus. The skull growth of W. madagascariensis clearly shows an allometric trend, but the fact that adults have more dermo-sensory grooves than juveniles suggests surprisingly that they may have become progressively more aquatic during growth. The ontogeny of W. madagascariensis is compared with that of other temnospondyls. Different longi-rostrine conditions are observed in Permian and Triassic stereospondylomorphs (archegosaurians and capitosaurians, respectively). They are interpreted as convergences rather than are a synapomorphy of the clade.