152
Journal of Paleontology 91(1):146–161
these divided ridges as taxonomic characters, based on obser- vations of variable twinning of the last ridge crest in the living Australian lungfish (Neoceratodus forsteri). Our survey of post- Triassic ceratodontids of North America suggests that this condition is often absent, or at least extremely rare, in most species. Here, we follow Milner and Kirkland (2006) and attribute taxonomic significance to this feature.
Ceratodus molossus new species Figure 2.2–2.7, Supplemental Data 3–5, Table 1
Holotype.—NCSM 30252, a robust, complete right pterygo- palatine plate with a partial pterygopalatine attached; Late Cretaceous, Mussentuchit Member, Cedar Mountain Forma- tion; 31km south of Emery, Emery County, Utah, U.S.A.
Diagnosis.—A ceratodontid bearing four primary ridge crests on the pterygopalatine plate, with the last being twinned slightly into an exposed ‘chin’ on the posterolabial corner; mesial mar- gin strongly linear. Both pterygopalatine and prearticular plates have a highly obtuse inner angle (ABC exceeding 130°) in combination with a strongly acute C1Cp angle (69–76°) and nearly planar occlusal surfaces, with negligible development of crests. The prearticular plate is characterized by rounded lingual and posterior margins, and a thick but short C1 ridge crest.
Occurrence.—Upper Cretaceous (Cenomanian), Cedar Moun- tain and Naturita formations, Utah, U.S.A. The referred pre- articular specimen (MNA.V.10649) is fromMNAlocality 1067, 2.4km northwest of Cannonville, Garfield County, Utah, U.S. A. The referred pterygopalatine plate (UMNH 16774) is also from the Naturita Formation, near Escalante, Garfield County, Utah, U.S.A.
Description.—The holotype specimen (NCSM 30252) is a large, right pterygopalatine plate with a complete occlusal surface. An additional specimen, very similar to the holotype, is also described here. UMNH 16774 is a large, right pter- ygopalatine plate, complete except for the tip of C1. Both known pterygopalatine plates (Fig. 2.2–2.5) strongly resemble the pterygopalatine plate of Ceratodus robustus (Knight, 1898, fig. 1), particularly in its large size, extreme flattening of the occlusal surface, shallow and rounded notches between ridges (greatest separation is between C1-C2), and squared posterior margin (Kirkland, 1987, pl. 1N; 1998, fig. 3I). These plates differs from C. robustus in having a twinnedCp ridge crest; also, ridge crests are thinner, withC3 andCp ridge crests slightly more distinct (the latter
noticeably shorter than in C. robustus). In addition, the elongate, finger-like C1 ridge crest of the holotype specimen is not observed in C. robustus. The large projection seenonthe mesiolingual border (junction of inner angle) of C. robustus is also present in NCSM 30252 and UMNH 16774, but is broader and does not project as far lingually. The prearticular plate referred to Ceratodus molossus
(MNA.V.10649, Fig. 2.6, 2.7) is complete; one complete and several partial prearticular plates of C. robustus are available for comparison (Kirkland, 1987, plate 1P–T; 1998, fig. 3H, J). MNA.V.10649 is slightly smaller than would be expected for the individual represented by the holotype, NCSM 30252, but it
is morphologically appropriate and would occlude well with the holotype, were it not for minor deformation of the prearticular tooth plate surface (see below). As with the upper plates, the prearticular tooth plate of C. molossus is similar to that of C. robustus, particularly in its massive construction, negligible expression of ridge crests on the occlusal surface, and the shallowness of the notches between ridges. MNA.V.10649 bears four ridges, of which C1 and C2 are widely spaced; the distance between C2-C3 is slightly greater than between C3-Cp, whereas C2-C4 tend to be more closely spaced, with more angulate intervening notches, in C. robustus. In both, the mesial margin differs from other North American species of Ceratodus in being rounded. In C. molossus, this rounded mesial margin is continuous with similarly curved lingual and posterior margins, giving the plate a semilunate shape. The lingual and posterior margins are straighter in C. robustus. TATE 3000 (Kirkland, 1998, fig. 3J), the only complete prearticular plate known for C. robustus, is proportionately more labiolingually expanded (especially on the mesial end, where C1 is particularly broad) than MNA.V.10649, but other specimens of C. robustus suggest variability in proportions of the prearticular plate. Intriguingly, the occlusal surface of MNA.V.10649 is
somewhat bowed, with the central portion being concave; a distinct trough (~4mm wide and 2–3mm deep) runs labiolin- gually across the center. These are readily identified as pathologies, of which a number are known for fossil and living lungfishes; the condition in MNA.V.10649 is closely matched in a specimen of Triassic Ceratodus kaupi (Kemp, 2001, fig. 6B; see also Kemp, 2003).
Etymology.—From molossus (Latin form of Greek Μολοσσfo), after the extinct breed of Greco-Roman fighting dog (De Prisco and Johnson, 1990), named in reference to Bulldog Bench near Cannonville, Utah, U.S.A., where the prearticular specimen (and other lungfish material) was found. The name is also an allusion to the presumed large and powerful feeding apparatus of the species, reminiscent of that of a bulldog or mastiff.
Materials.—Three nearly complete tooth plates, including the holotype: NCSM 30252 (holotype), a right pterygopalatine plate; UMNH 16774, a right pterygopalatine plate; and MNA. V.10649, a right prearticular plate.
Remarks.—With the addition of C. molossus, the already diverse ichthyofauna of the Naturita Formation (see Brinkman et al., 2013) now includes two species of Ceratodus. Ceratodus gustasoni Kirkland, 1987, like C. molossus, has flat, low-crested tooth plates; though represented by a number of specimens, only the lower (prearticular) tooth plate is known. It can be readily distinguished from that of C. molossus in that it is proportio- nately narrower labiolingually, with C1 being elongate and narrow, the crushing surface at the origin of ridge crests more mound-like, the lingual margin straight, and the C2-Cp ridge crests sharply pointed. Ceratodus molossus provides a striking point of contrast with the other recognized Cenomanian species, C. carteri Main, Parris, Grandstaff, and Carter, 2014, from the Woodbine Formation of Texas, which has small, sharply crested tooth plates.
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140 |
Page 141 |
Page 142 |
Page 143 |
Page 144 |
Page 145 |
Page 146 |
Page 147 |
Page 148 |
Page 149 |
Page 150 |
Page 151 |
Page 152 |
Page 153 |
Page 154 |
Page 155 |
Page 156 |
Page 157 |
Page 158 |
Page 159 |
Page 160 |
Page 161 |
Page 162 |
Page 163 |
Page 164 |
Page 165 |
Page 166 |
Page 167 |
Page 168 |
Page 169 |
Page 170 |
Page 171 |
Page 172 |
Page 173 |
Page 174 |
Page 175 |
Page 176 |
Page 177 |
Page 178 |
Page 179 |
Page 180 |
Page 181 |
Page 182 |
Page 183 |
Page 184 |
Page 185 |
Page 186 |
Page 187 |
Page 188 |
Page 189 |
Page 190 |
Page 191 |
Page 192 |
Page 193 |
Page 194 |
Page 195 |
Page 196 |
Page 197 |
Page 198 |
Page 199 |
Page 200 |
Page 201 |
Page 202 |
Page 203 |
Page 204 |
Page 205 |
Page 206 |
Page 207 |
Page 208
