The cranial morphology of a new genus of lungfish (Osteichthyes: Dipnoi) from the Upper Jurassic Morrison Formation of North America

ABSTRACT

Much of Mesozoic diversity within the lungfishes (Osteichthyes: Dipnoi) has traditionally been relegated to the genus Ceratodus, primarily on the basis of the highly stereotypical dental plates characteristic of post-Devonian lungfishes. The new genus Potamoceratodus contains the single species P. guentheri (Marsh, 1878), comb. nov. Newly discovered material allows clarification of the features of this species, including description of a complete skull roof and partial palate. The new genus can be differentiated from the European Ceratodus on the basis of characters of the skull roof, palate, and dentition, including lack of tubercular ornamentation of the skull roof, modest convexity of the dorsal skull roof, absence of sensory sulci anteriorly in the EF bone, and an enlarged and elongate anterior odontode series on the pterygoid dental plate. The North American Ceratodus record is reexamined in light of more complete material from the Temple Canyon localities of the Morrison Formation of Colorado, USA. Ceratodus is found to be an assemblage of forms with disparate cranial morphology. The succession of North American lungfish communities in the late Paleozoic and Mesozoic is most characteristic of serial replacement rather than in situ evolution, and it is possible that the isolation of North America subsequent to the breakup of Laurentia contributed to the regional extinction of lungfishes in North America.

ACKNOWLEDGMENTS

We would like to thank K. Carpenter for discovering the Temple Canyon localities and for providing access to the material, J. Kirkland, R. Lund, and E. Grogan for bringing our attention to this specimen, and the DMNH volunteers, especially G. Lindsey, for specimen preparation and further assistance in the field. We would also like to thank R. Lund, E. Grogan, M. Friedman, G. Lloyd, P. Ahlberg, D. Berman, J. Kirkland, D. Smith, J. Marcot, A. Jaszlics, I. Miller, K. Carpenter, K. Johnson, and J. Foster for helpful discussion, the University of Colorado, the Denver Museum of Nature and Science, and the Western Interior Paleontological Society for funding, and D. Engard and P. Monaco (Dino Depot), D. Grenard, H. Armstrong, and M. Smeins (Bureau of Land Management), City of Cañon City, and the State of Colorado for site access. We would also like to thank M. Wilson, A. R. C. Milner, and L. Cavin for suggestions, which greatly improved the manuscript.