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Journal of Paleontology 91(1):146–161
in the possession of tall ridges, with an acute C1Cp angle. The upper (pterygopalatine) plate attributed to the species here (Fig. 2.1) similarly has a twinned fifth ridge crest, giving this specimen six functional cutting surfaces. The upper plate, like the lower, has a slightly acute C1Cp angle and well-defined crests or ridges.
Materials.—UMNH-VP 16037 (holotype), prearticular plate with fused prearticular; and OMNH 69332, left pterygopalatine tooth plate.
Remarks.—We have emended the diagnosis of C. stewarti in order to account for the referred pterygopalatine plate, the morphology of which was anticipated by Milner and Kirkland (2006). The referred specimen extends the geologic range of C. stewarti upward to the Sinemurian. Milner and Kirkland (2006) also mentioned a prearticular tooth plate, MCZ 13865, from the Kayenta Formation of nearby northern Arizona (see Lucas et al., 2005), referring it to Ceratodus cf. C. guentheri. We agree with this assignment (see discussion).
Ceratodus kirklandi new species Figure 3.1–3.9, Supplemental Data 1, 2, Table 1
Holotype.—BYU 20808, right pterygopalatine plate with attached pterygopalatine, Early Cretaceous (Valanginian, based on Hendrix et al., 2015), lowest part of Yellow Cat Member, Cedar Mountain Formation; BYU locality 1667, 14km south- west of Cisco, Grand County, Utah, U.S.A.
Diagnosis.—A ceratodontid of moderate size; pterygopalatine plate with five ridges and a fifth ridge crest that is variably expanded into a flat crushing surface, with twinning present. Prearticular plate with four main ridges; fourth ridge always twinned, giving the specimens five ridge crests. Prearticular plates have a groove on the lingual edge of the occlusal surface to accommodate the inner angle of the upper tooth plate.
Occurrence.—Known only from the type locality, Grand County, Utah; Yellow Cat Member of the Cedar Mountain Formation (Lower Cretaceous).
Description.—The available sample of this species includes two pterygopalatine and five prearticular tooth plates, all with plate- bearing element attached. Pterygopalatine plates are similar in size and complete prearticular plates vary only slightly in maximum length (Table 1). All plates are sharply crested and angles between crests are relatively acute (see C1Cp values, Table 1). The occlusal surfaces on the margins of both the upper and lower plates show wear from the opposing tooth plates. In both plates the wear is angled, sharpening the ridges and crests with increased use. Wear on the lower plates is more heavily developed on the mesial side of the ridge crests, while on the
bearing up to eight denticles (C2 of BYU 20808). Crest five of BYU 20808 broadens into a flat surface distally and a faint sixth crest is present at the posterior margin (Fig. 3.1). The pterygopalatine (the bone to which the plate is fused) is undiagnostic, except for the pterygoid process, which is relatively small and pointed by comparison to other ceratodon- tids we have studied. Prearticular tooth plates also bear denticles on the crests, but they are less distinct and numerous (e.g., two are present on C2 of BYU 20813, Fig. 3.4) than on pterygopalatine plates. Four major crests are present, but the last is invariably twinned into two well-defined crests, giving a total of five. On the inferior side of the prearticular (Fig. 3.5), Ruge’s Ridge is developed underneath and medial to the C1–C2 ridges, as is commonly seen among North American ceratodontids.
upper plates it is heavier on the lingual side of the ridge crests. In general it appears that the pterygopalatine plates are more deeply incised than the prearticular plates. The pterygopalatine plates have five main crests, each
Etymology.—Named in honor of Dr. James Ian Kirkland, in recognition of his substantial contributions to the study of Mesozoic lungfishes and to knowledge of the Cedar Mountain Formation and its contained fossils.
Materials.—Seven tooth plates, including the holotype, as fol- lows: BYU 20807, an incomplete right prearticular plate with partial prearticular; BYU 20808 (holotype), a complete right pterygopalatine plate with preserved pterygopalatine; BYU 20809, complete left prearticular plate with partial prearticular; BYU 20810, a complete right pterygopalatine plate with partial pterygopalatine; BYU 20811, a complete left pterygopalatine plate with partial pterygopalatine; BYU 20812, an incomplete left prearticular plate, probably from an immature individual; and BYU 20813, a complete left prearticular plate with com- plete prearticular.
Remarks.—Ceratodus kirklandi is only the second North American, Early Cretaceous ceratodontid that is represented by multiple upper and lower plates from the same site. These specimens are probably the basis for listing of “Ceratodus undescribed new species” in the Yellow Cat Member, Cedar Mountain Formation, by Kirkland et al. (1999, p. 206). Like C. stewarti and Potamoceratodus guentheri, C. kirklandi possesses tall ridges with crest angles (C1Cp) being slightly acute. Ceratodus kirklandi is most similar to C. stewarti from the Moenave and Kayenta formations. Both species have prearticular tooth plates with a twinned fourth ridge crest, a condition unknown in any other North American species of Ceratodus (Milner and Kirkland, 2006). Similarly, the pter- ygopalatine fifth ridge is twinned in C. stewarti (based on the newly referred specimen,OMNH 69332) and variably twinned, at least, in C. kirklandi. Kemp (1997) argued against the use of
Figure 3. Ceratodus kirklandi n. sp. All specimens are from BYU locality 1667, Grand County, Utah; Yellow Cat Member, Cedar Mountain Formation, Lower Cretaceous (Valanginian). (1, 2) BYU 20808 (holotype), right pterygopalatine plate in occlusal and dorsal views, respectively; pter. = pterygoid. (3) BYU 20811, left pterygopalatine plate in occlusal view. (4, 5) BYU 20809, left prearticular plate in occlusal and inferior views, respectively. (6) BYU 20807, right prearticular plate in occlusal view. (7) BYU 20812, left prearticular plate in occlusal view. (8) BYU 20813, left prearticular plate in occlusal view. (9) BYU 20810, left prearticular plate in occlusal view.
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