Frederickson and Cifelli—Cretaceous lungfishes
lacking the twinned Cp crest on the lower plates. The specimen is from the Kayenta Formation of northern Arizona.
Late Jurassic.—No ceratodontids are yet recorded from the
Middle Jurassic, but the Morrison Formation (Kimmeridgian– Tithonian) has yielded four species. Ceratodus americanus Knight, 1898 is represented by UWM 2001b, a right pterygo- palatine plate lacking C1. Kirkland (1987) considered C. americanus a junior subjective synonym of Potamoceratodus guentheri (Marsh, 1878), based on specimens incorrectly referred to the latter species. Correcting this error, he later (Kirkland, 1998) transferred those specimens to a new species, Ceratodus fossanovum Kirkland, 1998 (misspelling in the original; intended naming for Como Quarry 9 would be fossanovem). Given the earlier referral of UWM 2001b, it is logical to wonder whether C. americanus might be a senior subjective synonym of C. fossanovum, which it closely resembles. Considering the incompleteness ofUWM2001b, we defer this taxonomic pitfall, and provisionally regard C. americanus as a nomen dubium (see Mones, 1989) for present purposes. Ceratodus fossanovum is the best-represented (in terms of
number of specimens) and most stratigraphically restricted of Ceratodontidae from the Morrison Formation: it is unequi- vocally known only from Quarry 9 (see Simpson, 1926; Carrano and Velez-Juarbe, 2006) and nearby, stratigraphically equiva- lent sites in the Como Bluff area, Wyoming. Available fossils show size variation, perhaps related to ontogenetic age. Ceratodus fossanovum resembles P. guentheri, differing in its larger size, more obtuse inner angle (ABC), and presence of a crushing platform on tooth plates. In these respects, it is morphologically closest to Early Cretaceous C. nirumbee n. sp. The record of Ceratodus frazieri Ostrom, 1970 in the
Morrison Formation is based on a lower tooth plate and nearly complete prearticular (SDSM 426) described by Pinsof (1983). As noted by Kirkland (1987), it is strikingly similar to specimens from the Cloverly Formation (Albian, Early Creta- ceous; see Fig. 2.12, 2.13, and Supplemental Data 8), including the holotype, YPM 5276. OMNH 04033, a pterygopalatine plate from the upper Morrison Formation of western Oklahoma, was also provisionally identified as C. frazieri (see Kirkland, 1998, fig. 3G). The specimen is broadly similar to KUVP 16226, an upper tooth plate from the Kiowa Shale (Lower Cretaceous) of Kansas, referred to C. frazieri by Schultze (1981). Both are rather flat, with a slightly excavated (concave) occlusal surface, and have relatively wide notches between the
ridges.OMNH 04033 is somewhat smaller and is labiolingually narrower, with a more tapering, less quadrate posterior margin, and with a somewhat thicker crown and distinct labial ridge crests. Whether these differences are ontogenetic or taxonomic cannot be determined with material in hand; we accept Kirkland’s (1998) referral for purpose of this review. Potamoceratodus guentheri (Marsh, 1878) (same as, or
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part of the Morrison Formation (Kirkland, 1987). Potamocer- atodus guentheri is also known from geographically and stratigraphically scattered sites in the unit (Kirkland, 1998), and it, or a closely similar species, is represented in the Early Jurassic of Arizona. Two species with morphologically similar tooth plates are also known from the Cretaceous of Texas (Main et al., 2014; Parris et al., 2014). Ceratodus robustus Knight, 1898 is represented by a small
sample that nonetheless includes all upper (pterygopalatine, vomerine) and lower (prearticular) tooth plates, as well as specimens exhibiting a range of variation (Kirkland, 1987, 1998). Ceratodus robustus is known from several sites, all in the Morrison Formation of Wyoming. Until now, it has been regarded as unique among North American species of Ceratodus, and has been occasionally cited in connection with possible relatives from other landmasses (e.g., Kirkland, 1987, 1998; Kemp, 1993; Pardo et al., 2010). Ceratodus molossus n. sp. is closely similar, and suggests that the clade survived into the Late Cretaceous.
Early Cretaceous.—Werecognize six species of Ceratodus
from geographically and stratigraphically scattered sites in the Early Cretaceous of North America. Of these, C. kirklandi n. sp.,C. kempae n. sp. (both from the Valanginian of Utah), and C. nirumbee n. sp. (Albian, Montana) are described herein and
including Ceratodus felchi Kirkland, 1987) was the first dipnoan to be named from the Morrison Formation. It is a high-crested form with slightly acute C1Cp angle, and is among the smallest of North America’s post-Triassic lungfish; it is also notable in being the only North American ceratodontid known by cranial material (Pardo et al., 2010). A reasonable sample of tooth plates is known from Felch Quarry in the lower
need no further comment. Ceratodus frazieri Ostrom, 1970, the first ceratodontid to be named from the Early Cretaceous of North America, was recognized on the basis of a left prearticular plate, YPM 5276 (Ostrom, 1970, plate 9A), from unit V of the Cloverly Formation, Wyoming. Kirkland (1987, plate 1F) illus- trated another prearticular plate (MOR 367). Oreska et al. (2013) referred several incomplete tooth plates to C. frazieri. The most complete and the only of these to be illustrated, USNM 546680 (Oreska et al., 2013, fig. 5A), is consistent with C. frazieri in being low crowned with rather robust, short ridges, though it is not sufficiently complete for secure identification. Interestingly, it is small (maximum preserved length =26mm), and may represent an immature individual. An additional spe- cimen (OMNH60408; Fig. 2.12, 2.13, and SupplementalData 8) from the Cloverly Formation at OMNH locality V1075 in Big Horn County, Montana, resembles the holotype and can unam- biguously be referred to C. frazieri. Schultze (1981) referred to C. frazieri alarge, flat-crowned pterygopalatine plate (KUVP 16262) from the Kiowa Formation (Albian) of western Kansas. The age and morphology of the specimen are appropriate for the species, and we follow Kirkland (1987, 1998) in accepting this
referral.Kirkland (1987) also suggested possible referral ofUCM 49389 (large tooth plate fragments) to this species. The fossils are said to come from the lower part of the Cedar Mountain Forma- tion, central Utah. This unit includes several members, collec- tively spanning much of the Early Cretaceous and extending to (or just past) the Early-Late Cretaceous boundary (e.g., Kirkland et al., 1997, 1999).We have not studied the material, and given that the specimens are incomplete and were not illustrated, they can be ignored for present purposes. Ceratodus kranzi Frederickson, Lipka, and Cifelli,
2016 is based on an incomplete pterygopalatine plate, USNM 508543, from the Arundel Clay facies (Aptian–Albian) of the Potomac Formation, Maryland. This specimen represents a
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