Journal of Paleontology, 92(2), 2018, p. 146–156 Copyright © 2017, The Paleontological Society 0022-3360/18/0088-0906 doi: 10.1017/jpa.2017.79
New Pennsylvanian coleoids (Cephalopoda) from Nebraska and Iowa, USA
Royal H. Mapes1 and Larisa A. Doguzhaeva2 1Division of Paleontology, American Museum of Natural History, CPW@79th Street, New York, NY 10024 ⟨
mapes@ohio.edu⟩ 2Department of Palaeozoology, Swedish Museum of Natural History, Stockholm, Sweden ⟨
Larisa.Doguzhaeva@
nrm.se⟩
Abstract.—Four rare Pennsylvanian (Stark Shale: Pennsylvanian, Missourian [=Kasimovian]) coleoids from Nebraska and Iowa, which are preserved as flattened partial phragmocones and body chambers associated with three-dimensionally fossilized ink sacs, are herein described as Pabianiconus starkensis new genus new species, Nebraskaconus whitei new genus new species, and Starkites compressus new genus new species. One specimen that is missing most of the phragmocone, is provisionally assigned to Donovaniconus. The fossils are assigned to the Coleoidea because of the presence of ink-filled sacs in the body chamber region of the conch. Additionally, eight fragmented and flattened phragmocones and body-chamber clusters with similar morphologies, including some with ink fragments and arm hooks, are assigned to the Coleoidea, but are not named because of their fragmentary condition. On most of the eight specimens, the shell material is associated with other unidentified finely macerated material, which suggests these fossils are probably either ejectoid masses or coprolites from coleoid predators and/or scavengers. However, the new genera named above appear to have been deposited as complete animals, based on the presence of the ink-filled sacs that are in the body chambers. With their body chamber and phragmocone morpho- logies, these rare coleoid taxa provide valuable information about conch variability within the Carboniferous evolutionary radiation of coleoids.
Introduction
Description of the Upper Mississippian coleoids Hematites, Paleoconus, and Bactritimimus by Flower and Gordon (1959) marked the beginning of recognition of coleoid cephalopods in the Paleozoic. Gradually, over the past 60+ years since their report, a modest number of coleoids have been recognized from North American upper Paleozoic strata. For the taxa that have been described, see the classification in Doguzhaeva et al. (2010) and subsequent reports by Mutvei et al. (2012) and Doguzhaeva and Mapes (2015). The Pennsylvanian age flattened and partial phragmocone
specimens from Nebraska and Iowa, described herein, lack a well-defined rostrum like the coleoid specimens described by Flower and Gordon in 1959. However, these specimens can be confidently assigned to the Coleoidea because they preserve perfectly shaped, flask-like organs filled with ink, and ink in the Cephalopoda is only known in the Coleoidea. The preservation of coleoid ink as well as the factors that controlled the three- dimensional preservation of ink in the ink sac within the extre- mely compressed phragmocones, and body chambers were reported by Doguzhaeva et al. (2002b). The ink ultrastructure of one of the Stark coleoids fossils was examined under scanning electron microscope (Doguzhaeva et al., 2004, fig.1) and com- pared with that of modern squids and Jurassic squid-like coleoids (Doguzhaeva et al., 2004). Because of the rarity of the Stark specimens and similarities seen on other ink-bearing taxa, additional destructive ink testing was not attempted. At this time, only one other taxon from the Nebraska and Iowa coleoid
collection from the Stark Shale has been described and named Flowerites bellevuensis by Mapes et al. (2010a). However, that generic name proved to be preoccupied and the new generic designation Flowericonus was proposed to replace the pre- occupied name (Doguzhaeva and Mapes, in press). Mapes et al. (2010a) proposed several scenarios to explain the morphology of Flowericonus. However, that taxon remains a problematic specimen in that the three-dimensional ink sac appears to be placed under the septa in the bullet-shaped phragmocone, which is somewhat similar to that seen in the mature conchs of the nautiloid order Ascocerida. Since this morphology has not been reported in any coleoid from any age, interpretation of the conch of Flowericonus remains debatable at this time. In spite of the fact that Paleozoic coleoid cephalopods are
extremely rare all over the world, the Carboniferous coleoids discovered from the central part of USA in the past 40 years demonstrate their remarkable diversity. Analysis of the Upper Paleozoic coleoids from this region indicates that an evolutionary radiation took place in the coleoid cephalopod lineage during the upper Paleozoic (Doguzhaeva et al., 2010). This evolutionary radiation hypothesis is based on amosaic combination of the “old” (typical for the externally shelled cephalopods as seen in the orthoceratid and bactritoid cephalopods) and “new” (typical for the internally shelled cephalopods as new morphologic features not previously seen in the cephalopod lineage) morphological traits, the parallel appearance and variations of newmorphological features, and relatively rapid changes in basic shell morphology. The Pennsylvanian genus Donovaniconus Doguzhaeva, Mapes, and Mutvei, 2002a from Oklahoma exemplifies the
146
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
