Comparative rib material analyzed.

Abbreviations are as in Table 2. AMNHN: American Museum of Natural History, New York, USA; IPB: Institute for Paleontology, University of Bonn, Germany; MHBR: Muséum d’Histoire Naturelle du Havre, France; NSM: National Science Museum, Tokyo, Japan; RMM: former Red Mountain Museum, Birmingham, Alabama, USA (the collection is currently housed at the McWane Science Center, Birmingham, Alabama, USA); TMM: Texas Memorial Museum, Dallas, Texas, USA; UW: University of Wisconsin, Madison, Wisconsin, USA. The ontogenetic stage is indicated for non-adult specimens.