Peng et al.—Revision of oryctocephalid genra
937
Figure 3. Reconstructions of Arthricocephalus chauveaui (1) based on NIGP 163354, and Oryctocarella duyunensis (2) based on NWU-DYXJT 1823, both from the Balang Formation of western Hunan, China. These species show differences in glabellar outline (forwardly expanding or pestle-shaped, 1, compared to cylindrical, 2); development of the glabellar furrows (transglabellar, 1, compared to pit-like, 2); course of the axial furrow (curved, 1, compared to straight, 2); course of the facial suture (gonatoparian, 1, compared to proparian, 2); shape of the anterior cranidial border (upturned posterolaterally, 1, compared to anteriorly, 2); position of the palpebral lobe (situated at the level of the glabellar mid-point, 1, compared to located anteriorly, 2); presence,1, or absence, 2, of fulcra; thoracic segmentation (eight segments, 1, rather than 11 segments, 2); tips of pleurae (pointed, 1, rather than slightly rounded, 2); size and segmentation of pygidium (isopygous, with five pleurae, 1, compared to micropygous, with three pleurae, 2); pygidial interpleural furrows (faint, 1, rather than well defined, 2); pygidial border (upturned, 1, rather than absent, 2); development of the posterior pygidial margin (equally curved, 1, rather than with a median notch, 2); and surface prosopon (smooth to finely granulose, 1, as compared to coarsely and densely granulose, 2; surface granulation on the reconstruction of each species has been omitted).
although it has long been considered to be a meraspid of this species (e.g., Lane et al., 1988;Blaker and Peel, 1997;McNamara et al., 2003). The specimen also differs considerably from speci- mens on Bergeron’s (1899) slab reassigned to Oryctocarella duyunensis. The specimen is here reassigned to Duyunaspis
duyunensis Zhang and Qian in Zhou et al., 1977 (p. 132, pl. 41, figs. 5, 6), the type species ofDuyunaspis. The exoskeleton differs from both A. chauveaui and O. duyunensis in having a pro- portionally large glabella that is wider than the fixigena; shallow and weakly impressed glabellar furrows; a proportionally wide thoracic axis that is nearly as wide as the pleural area; and a relatively small pygidium with a broad axis. The specimen of D. duyunensis has a medial notch on the posterior margin of the pygidium, similar to O. duyunensis, but the pygidial axis in specimens of O. duyunensis is much narrower, being only about half as wide as the pleural area. The thorax of the smallest exoskeleton on Bergeron’s slab has fulcrate segments, similar to A. chauveaui, but the fulcra in the smallest specimen lie much closer to axial furrow than they do in the largest exoskeleton. We conclude that Bergeron’s (1899) original illustration
and description of A. chauveaui are based principally on the largest exoskeleton in the type series. According to Article 74.6.1 of the International Code of Zoological Nomenclature (ICZN, 1999), which states that “The inference that the speci- men is a ‘holotype’ or ‘the type’ may be by reference to an illustration or description of specimen,” the largest exoskeleton on Bergeron’s slab is inferred as ‘type’ of A. chauveaui.
In accordance with Article 74.6, “the assumption that the species-group taxon was based upon a single type specimen is deemed to have designated that specimen as the lectotype.” For these reasons, the largest exoskeleton on Bergeron’s (1899) limestone slab (E.M. 90001a) is designed the lectotype of Arthricocephalus chauveaui. Arthricocephalus is considered to be a monotypic genus. An external mold of a large pygidium (E.M. 90001g;
Figs. 1.2, 2.11) on Bergeron’s (1899) slab remains assigned to Arthricocephalus chauveaui; it is a paralectotype. Other scler- ites on the slab, which are presumed to be part of Bergeron’s suite of examined specimens and all originally referred to A. chauveaui, are also considered to be paralectotypes of A. chauveaui. All of these specimens, however, are here reas- signed as either Oryctocarella duyunensis (E.M. 90001b– 90001e, 90001h) or Duyunaspis duyunensis (E.M. 90001f).
Incorrect designation of lectotype
Circumstances surrounding the designation of a lectotype of Arthricocephalus chauveaui by Lane et al. (1988), and sub- sequent treatment of Bergeron’s (1899) suite of material, has resulted in ambiguity of the concepts of both A. chauveaui Bergeron, 1899 and Arthricocephalus Bergeron, 1899. Photographs of some Bergeron’s sclerites were first published by Lane et al. (1988). In that same article, Lane et al. (1988, p. 558) stated that they accepted the specimen upon which
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 |
Page 209 |
Page 210 |
Page 211 |
Page 212 |
Page 213 |
Page 214 |
Page 215 |
Page 216 |
Page 217 |
Page 218 |
Page 219 |
Page 220 |
Page 221 |
Page 222 |
Page 223 |
Page 224 |
Page 225 |
Page 226 |
Page 227 |
Page 228 |
Page 229 |
Page 230 |
Page 231 |
Page 232 |
Page 233 |
Page 234 |
Page 235 |
Page 236 |
Page 237 |
Page 238
