The Skull Morphology and Estivation Burrows of the Permian Lungfish, Gnathorhiza Serrata

The Permian lungfish, Gnathorhiza, has been of particular interest to paleontologists because of its possible relationship to the modern lepidosirenid lungfish and because of its burrowing habits. New localities in the Wellington Formation of north-central Oklahoma have yielded numerous estivation burrows containing the articulated skull bones of these lungfish. The skull of Gnathorhiza serrata is described and a phylogeny is proposed for the post-Permian lungfish. The phylogeny, based primarily on skull roof bone patterns, proposes Gnathorhiza as an ancestral type leading to the modern Protopterus and Lepidosiren, with a second line, separate since the start of the Mesozoic, leading to Neoceratodus. The sectioned Permian estivation burrows show a number of features similar to the burrows of modern lepidosirenids. The burrow form and lithology suggest that Gnathorhiza used its mouth in burrowing and that it stood on its tail in the burrow during estivation. Different modal sizes of the burrows at different sites indicate the segregation of the burrowing fish into brood groups. Intersecting burrow structures show that certain localities were the sites of repeated cycles of burrowing, indicating alternating wet and dry seasons during Wellington time.