A new species of the Rhytidosteidae from the Lystrosaurus zone and a review of the Rhytidosteoidea

Cosgriff, John W.
Zawiskie, John M.
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Bernard Price Institute for Palaeontological Research
Pneumatostega potamia, a new rhytidosteid temnospondyl from the Lystrosaurus Zone, is described and compared with the other species of the family. Its evolutionary relationships and adaptive morphology are considered. The closest affinity is with the species of Deltasaurus from the Lower Triassic of Australia, the next closest with the species of Peltostega from the Lower Triassic of Spitsbergen and the most distant with Rhytidosteus capensis, a Karoo species which is probably also from the Lystrosaurus Zone. As with other species of Rhytidosteidae, for which both taphonomic and adaptive morphologic evidence is available, P. potamia was, apparently, a fluviatile, subsurface, piscivorous temnospondyl regarding its primary and preferred habitat. Proceeding from information contributed by the new species, the taxonomic structure of the Rhytidosteoidea is reorganised and expanded and new diagnoses are provided for both this superfamily and its contained families. The family Rhytidosteidae now includes Deltasaurus kimberleyensis, D. pustulatus, Peltostega erici, P. wimani, Pneumatostega potamia and Rhytidosteus capensis. A new family, Indobrachyopidae, is created to include Derwentia warreni (removed from the Rhytidosteidae), Indobrachyops panchetensis, Mahavisaurus dentatus, Mahavisaurus (Lyrosaurus) australis and Rewana quadricuneata. Laidleria gracilis is removed from the Rhytidosteoidea. Latiscopus disjunctus and Almasaurus habbazi possess some features in common with members of the superfamily but are too distinct in most features to be considered rhytidosteoids. Taxonomic distances among the rhytidosteids and indobrachyopids are established by a computer program. A phylogeny of the superfamily is constructed and this is consonant with the stratigraphic and geographic occurrences of the species. A southern origin for the superfamily with a generally northward dispersal is proposed.
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temnospondyl; Lystrosaurus Zone