Frederickson and Cifelli—Cretaceous lungfishes


of ~ 4 m (Shimada and Kirkland, 2011). Smaller species with high-crested tooth plates—suggestive of shearing function— may have relied more heavily on fare having negligible miner- alized tissue, such as soft-bodied invertebrates (Parris et al., 2007). Dietary preference also presumably varied ontogeneti- cally, as in the living Australian lungfish (Neoceratodus forsteri), whose dentition progresses from sharp cones, suitable mainly for apprehending food items, to well-worn crushing plates, which are capable of processing mollusks and other hard-bodied prey (Kemp, 1986). Lungfishes were geographically and stratigraphically


widespread in the Cretaceous of North America, and include fossils ranging from the Albian of Montana and Wyoming (Ostrom, 1970; Oreska et al., 2013) to the Late Cretaceous (probably Campanian) of New Jersey (Parris et al., 2004). Occurrences within this broad temporal and geographic range are sparse and rare, however. All but two are from western North America (Parris et al., 2004; Frederickson et al., 2016), and overall taxonomic representation is meager. Herein we report new dipnoan fossils from Cretaceous units spanning the Valanginian–Cenomanian of North America’sWestern Interior Basin (see Kauffman and Caldwell, 1993). These include representation of four new species named herein: Ceratodus kempae n. sp., C. kirklandi n. sp., C. molossus n. sp., and C. nirumbee n. sp. We also add to knowledge of Jurassic C. stewarti Milner and Kirkland, 2006 by referring an upper tooth plate to the species. These new fossils, together with cri- tical appraisal of other occurrences, provide basis for evaluating ceratodontid diversity (morphologic and taxonomic) through the Cretaceous of North America.


Materials and methods


Standardized angles and reference points (Kirkland, 1987 and references therein; abbreviations for structures used as basis for measuring angles are illustrated in Fig. 1) were measured from photographs of specimens described herein (Table 1). We pre- sent these data mainly to provide consistent frame of reference with respect to previous studies on North American cer- atodontids (e.g., Kirkland, 1987, 1998; Parris et al., 2004, 2014; Main, 2013; Main et al., 2014). Phylogenetic utility of these measurements is limited, largely owing to a lack of basis for assessing variability: most North American taxa are known by one or a few specimens. Further, in Australian lungfishes, angles of the ridge crests can be very similar, even in visually distinct tooth plates (Kemp and Molnar, 1981; Kemp, 1997). In this study, we compared gross morphology using the published descriptions and anatomical terminology of Kirkland (1987). Since there is currently no single set of characters that can be used to accurately diagnose all fossil lungfish species, qualita- tive approaches that follow the outlines suggested by Kirkland (1987) and Kemp (1997) are used to define the taxonomic boundaries between species. Finally, no attempt is made to reconstruct phylogenetic relationships, because most of these specimens are composed solely of tooth plates having limited morphological information. Except where indicated otherwise, specimens reported herein were collected from Federal lands administered by the


147


Figure 1. A hypothetical Ceratodus right prearticular plate showing orientation, basis for angles, and abbreviations for crests, following Kirkland (1987, 1998).


U.S. Bureau of Land Management, which maintains and restricts access to specific locality coordinates. For southern and central Utah, the rock unit traditionally cited as the Dakota Formation is herein termed the Naturita Formation (see Young, 1960; Carpenter, 2014).


Repositories and institutional abbreviations.—Specimens mentioned in this study are deposited in the following institu- tions: AMNH, American Museum of Natural History, New York, New York, U.S.A.; BYU, Paleontological Collections, Brigham Young University, Provo, Utah, U.S.A.; DMNS, Denver Museumof Nature and Science, Denver, Colorado, U.S. A.; KUVP, Vertebrate Paleontology Collection, University of Kansas Natural History Museum, Lawrence, Kansas, U.S.A.; MCZ, Museum of Comparative Anatomy, Harvard University, Cambridge, Massachusetts; MNA, Museum of Northern Arizona, Flagstaff, Arizona, U.S.A.; MOR, Museum of the


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