164 Materials and methods
The specimens described here were found associated in large quarry blocks, consisting primarily of crossbedded sandstone, siltstone, and conglomerate. The articulated specimen was found with the ventral surface exposed, although the original orientation of the host block is not known. Fossils are identified in the field and removed by using a rock saw to cut out blocks of matrix and fossils, which are then transported to the NCSM. There, preparation consists of removing matrix with tungsten- carbide pins and air scribes, and specimens are consolidated using polyvinyl acetate (VINAC® B-15). The specimens were photographed using a Nikon D60 camera, with images manipulated in Adobe Photoshop and drawings accomplished using Adobe Illustrator. The material is mostly in the form of disassociated osteo-
derms (scutes) and occasional vertebral and limb elements, but articulated material includes an almost complete presacral ske- leton, including much of the armor of one small individual. Numerous other elements, some isolated and some associated, were preserved separately in three other boulders. We recognize two distinctive aetosaur taxa in the material (Fraser et al., 2006; Schneider et al., 2011; Heckert et al., 2012), with the majority of the fossils from the same taxon as the articulated skeleton, but some representing another, larger, taxon recently named Gorgetosuchus (Heckert et al., 2015). We follow Heckert and Lucas (1999) and refer to the longitudinal series of osteoderms as “columns” and transverse series as “rows.” Thus an aetosaur carapace typically consists of two columns each of paramedian and lateral osteoderms and eight or more columns of ventral osteoderms. Rows typically correspond 1:1 with vertebrae, especially in the thoracic and caudal series, although there are exceptions (Long and Murry, 1995). Osteoderms from different parts of the body are identified as “cervical, thoracic, sacral, caudal, and appendicular” as appropriate, following Long and Ballew (1985; Heckert and Lucas, 2000; Parker, 2007). We use dorsal and ventral “aspect” to describe the views of the top and bottom of the articulated skeleton, and “view” to indicate observations of elements as if in life position. The order of discussion of preserved skull elements is the same as used by Small and Martz (2013).
Repositories and institutional abbreviations.—The specimens described here, including the holotype, are reposited at the North Carolina Museum of Natural Sciences (NCSM) in
Raleigh, North Carolina, where detailed locality data are also on file. The type species of Coahomasuchus kahleorum Heckert and Lucas, 1999, which is the only other specimen of the genus, is reposited at the New Mexico Museum of Natural History and Science (NMMNH), in Albuquerque, New Mexico. We also make reference to a specimen housed at the Texas Memorial Museum (TMM) in Austin, Texas.
Systematic paleontology
Superorder Archosauria Cope, 1869 Order Suchia Krebs, 1974
Suborder Aetosauria Marsh, 1884
Journal of Paleontology 91(1):162–178 Family Stagonolepididae Lydekker, 1887 Genus Coahomasuchus Heckert and Lucas, 1999
Type species.—Coahomasuchus kahleorum Heckert and Lucas, 1999 from the Colorado City Formation, west Texas, by original designation.
Other species.—Coahomasuchus chathamensis n. sp., described here.
Diagnosis.—Genus of aetosaur distinguished by its relatively small (<1.5m adult size) body and characterized by dorsal paramedian osteoderms with extremely faint ornamentation, especially on the presacral series, typically expressed as a subdued boss or knob from which elongate, subradial ridges emanate laterally, with smaller, and more pitted, ornamentation medially. All but the apparent small size are apomorphic for the genus.
Occurrence.—Known from the Colorado City Formation (Dockum Group), west Texas (Heckert and Lucas, 1999) and the Pekin Formation of North Carolina (described here).
Coahomasuchus chathamensis new species Figures 2–6
Holotype.—NCSM 23618, an incomplete, articulated skeleton (Figs. 2–5) from the Upper Triassic Pekin Formation, NCSM locality 1902, Chatham County, North Carolina.
Diagnosis.—A species of Coahomasuchus distinguished from the type species, C. kahleorum, by proportionately wider dorsal paramedian osteoderms ( ~10 to 35% wider for homologous osteoderms; maximum width:length ratio of 3.6 or more) and ventral thoracic osteoderms that are rectangular (~1.5x wider than long), not square. Autapomorphies of C. chathamensis include a surangular with a long ventral process extending as far as, or farther than, the dorsal process, and the wide thoracic ventral osteoderms.
Occurrence.—Known solely from the Upper Triassic Pekin Formation of Chatham County, North Carolina. The quarry yielding these specimens is in the upper portion of the Pekin Formation, which is currently considered some of the older Upper Triassic strata in the Newark Supergroup in that it is Carnian in age (Whiteside et al., 2011, table s2), see discussion in “geologic setting” for more details. Detailed locality data for NCPALEO1902 are on file at NCSM.
Description.—The holotype, NCSM 23618 (Figs. 2–5) com- prises the anterior half of an articulated, dorso-ventrally crushed skeleton that has been prepared in dorsal and ventral aspect (Figs. 2, 3). The posterior half of the skull and lower jaws have been prepared in left and right lateral views as well (Figs. 4, 5). Posterior to the skull approximately 15 rows of paramedian osteoderms are evident (Fig. 3). Assuming a 1:1 ratio of osteo- derm rows to vertebrae (typical, but not universal for aetosaurs— Walker, 1961; Long and Murry, 1995; Desojo et al., 2013;
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
