The Permo-Carboniferous genus Sagenodus and the beginning of modern lungfish

Abstract

The lungfish Sagenodus is a widespread Permo-Carboniferous genus found in Europe and North America. Important localities in the U.S.A. include Middle Pennsylvanian coals near Linton, Ohio, Upper Pennsylvanian deposits near Robinson and Hamilton, Kansas, and Peoria, Illinois; Lower Permian sediments near Cameron, Ohio; and Lower Permian “Red Beds” of Texas and Oklahoma. At least three species of Sagenodus were present in North America S. copeanus, S. periprion, S. serratus). S. ohiensis is represented solely by one skull. Knowledge of the osteology of Sagenodus is enhanced by the study of well-preserved but disassociated elements from Robinson, Kansas (S. copeanus) and Little Bitter Creek, Texas (S. serratus). The orbital series is now known to be comprised of six elements and the sensory canal system is more complex than previously realized. The only known articulated skeleton of this genus, from Hamilton Quarry, Kansas, permits a restoration of the entire animal including the median fins. The dorsal and anal fins are not separate; there is instead, a continuous fin around the caudal end of the body, as found in other post-Devonian lungfishes. Sagenodus is structurally intermediate between more primitive Devonian dipnoans and post-Paleozoic lungfishes. Evident trends can be seen in the reduction of bone (both number of bones and degree of ossification), the loss of cosmine, the nature of the scales, the structure and histology of tooth plates, and the configuration of the median fins. Sagenodus is a member of a euryhaline faunal assemblage that can be found from shallow marine to freshwater deposits.