Frederickson and Cifelli—Cretaceous lungfishes Ceratodus nirumbee new species Figure 2.8, 2.9, Supplemental Data 6, Table 1
Holotype.—OMNH 34765, a complete right prearticular plate, Early Cretaceous (Albian, see Cifelli and Davis, 2015), lower unit VII (stratigraphic nomenclature of Ostrom, 1970), Cloverly Formation; OMNH locality V1061, 11 km east northeast of Edgar, Carbon County, Montana, U.S.A.
Diagnosis.—A tall-crested, medium-sized ceratodontid most closely resembling C. fossanovum, differing in the extreme mesial placement of Ruge’s Ridge; ridge crests more distinct, particularly near area of common origin, with narrower crest Cp and better developed C3-Cp notch; and a more angulate, less rounded posterolingual margin.
Occurrence.—Known only from the type locality, Cloverly Formation (Albian, Early Cretaceous), Carbon County, Montana, U.S.A.
Description.—OMNH 34765 is a complete right prearticular tooth plate with fused prearticular; it is slightly water-worn, lacking the anterior and posterior processes of the prearticular, and has well-developed occlusal wear. The plate bears four tall, well-defined ridge crests and a small crushing surface at the origin of crests C1-C2. Crest C1 bears three denticles in a single row; four denticles in a non-linear arrangement are present on C2;C3-C4 begin with double rows of denticles and have an irregular arrangement. OMNH 34765 represents a medium- sized lungfish, larger than Potamoceratodus guentheri and smaller than Ceratodus gustasoni, most resembling C. fossanovum from the Morrison Formation. OMNH 34765 possesses similar ridge crest angles (Table 1) to C. fossanovum, and falls within the range of variation for this species (see values for C. “guentheri” in Kirkland, 1987). However, OMNH 34765 differs from C. fossanovum based on suite of characters not found on any of the published specimens from the Jurassic. Ceratodus fossanovum possesses a well-developed crushing platform on the lingual side of prearticular tooth plates, joining the origins of the ridges for the C3 and Cp ridge (Kirkland, 1987, plate 1D), which is not developed in OMNH 34675. This plat- form can be seen in lingual view as a second convexity, more posterior to the tall platform formed from the intersection of the C1 and C2 ridges in C. fossanovum. The notch (sulcus) between the C3 and Cp ridge crests is deeper and better developed in OMNH34765 than in C. fossanovum. On the inferior surface of the underlying prearticular (Fig. 2.9), OMNH 34765 has a well- developed median trough or groove that terminates mesially at Ruge’s Ridge, which is more distally placed in other species.
Etymology.—From the Crow, Nirumbee, Little People of the Pryor Mountains; dwarves or devils with a ferocious tempera- ment, sharp teeth, and a predilection for meat (Murray, 2008). Allusion is to the presumed feeding habits of the species and to proximity of the type locality to the Pryor Mountains, specifi- cally what is now Chief Plenty Coups State Park, where the legendary Crow leader drew inspiration from the Nirumbee (Linderman, 1957).
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Remarks.—Ceratodus nirumbee cannot be readily confused with the other ceratodontid known from the Cloverly Forma-
tion, C. frazieri Ostrom, 1970, which is characterized by large, flat-crowned tooth plates (Fig. 2.12–2.13). Oreska et al. (2013) mentioned two ceratodontids among the specimens they col- lected via underwater screen washing of rock matrix from the Cloverly Formation: C. frazieri and Ceratodus cf. P. guentheri.
The specimens are too fragmentary to be identified with con- fidence, but USNM 546679 (Oreska et al., 2013, fig. 5B) much resembles OMNH 34765, holotype of C. nirumbee, particularly in the presence of a long, thin C3 ridge crest that is subequal to the C2 ridge crest. We provisionally consider this specimen, at least, as belonging to the species. Similarly, Bonde (2008) and Bonde et al. (2008) briefly described and figured a pterygo- palatine tooth plate (VOF-2005-03-2A-001) from the Albian- aged Willow Tank Formation of southern Nevada, similar in shape to the holotype of C. nirumbee. If this specimen does in fact represent an upper plate for C. nirumbee, it vastly increases our knowledge of the morphology for this species. Until more robust comparative studies can be done, we informally attribute this specimen to the species as well.
Ceratodus kempae new species Figure 2.10, 2.11, Supplemental Data 7, Table 1
Holotype.—BYU 20814, right pterygopalatine tooth plate and attached pterygopalatine, complete except for C1; Early Cretaceous (Valanginian, see Hendrix et al., 2015); BYU locality 1783, 16.7 km southwest of Cisco, Grand County, Utah, U.S.A.
Diagnosis.—Moderate-sized species of Ceratodus, slightly smaller than C. gustasoni, which it resembles in having little surface relief on tooth plate crowns, lack of denticles on ridge crests, obvious circumdenteonal islands present on occlusal surface, and ridges that narrow and are pointed labially. Differs from C. gustasoni and other flat-plated North American species of Ceratodus in having less obtuse C1-Cp angle, slightly better- developed ridge crests, serrated labial plate margin (angulate ridge termini separated by angulate notches), and presence of prominent vertical wear facets between ridges.
Occurrence.—Known only from the type locality, Yellow Cat Member, Cedar Mountain Formation (Valanginian, Lower Cretaceous), Grand County, Utah, U.S.A.
Description.—BYU 20814 is missing C1 of what was originally a five-crested right pterygopalatine tooth plate. The preserved part of the mesial margin indicates angle ABC to be 111° (Table 1), less than the flat-crowned C. gustasoni or C. frazieri (Kirkland, 1987, table 1). The specimen is of moderate size, considerably smaller than in C. frazieri and larger than P. guentheri or C. kirklandi. The occlusal surface is low and undulating, with a modestly developed central mound, where the ridges originate at the mesiolingual corner of the plate. Ridge crests are faint but are better developed than in the most closely similar taxon, C. gustasoni (Fig. 2.14, 2.15). All of the labial ridge tips are distinctly angular, as are the intervening notches, such that the labial margin of the plate has a serrated
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