LoDuca and Tetreault—Paleobiology of a new Silurian macroalga
Systematic paleontology Order Dasycladales Pascher, 1931
Family Triploporellaceae (Pia, 1920) Granier and Bucur in Granier et al., 2012
Tribe Triploporelleae (Pia, 1920) Bassoullet et al., 1979
Subtribe Triploporellinae (Pia, 1920) Bassoullet et al., 1979 Genus Wiartonella new genus
Type species.—Wiartonella nodifera n. sp., by monotypy. Diagnosis.—As for type species, by monotypy.
Etymology.—In reference to the geographic origin of thematerial, near the town ofWiarton, Ontario, Canada.
Occurrence.—Known only from the Eramosa Formation exposed in the northernmost pit of the Owen Sound Ledgerock Ltd. quarry, 4 km northwest of Wiarton, Ontario.
Figure 2. Wiartonella nodifera n. gen. n. sp. from the Silurian Eramosa Formation, Wiarton, Ontario: (1, 2) thalli with holdfast (arrow) in contact with poorly preserved brachiopods (ROM 63793, ROM 63802). (3) Composite EDS elemental map of a part of ROM 63803 (arrow at lower left in 3.9). Scale bar is (1, 2) 5mm; (3) 0.33mm.
Materials and methods
The study material comprises some 30 slabs, most of which have multiple specimens distributed across the bedding plane surfaces. More than 60 specimens in total were examined. High-resolution morphometric data were collected from digital images using the open source program ImageJ. Electron microscopic study of the material was conducted
using a Hitachi S-3200N at the Electron Microbeam Analysis Laboratory, Department of Earth and Environmental Science, University of Michigan and an FEI Quanta 600F at the University of Missouri Electron Microscopy Core. All specimens were imaged uncoated under low vacuum, and backscattered electron images were obtained using an accelerating voltage of 15 keV. EDS elemental maps (University of Missouri) were collected uncoated under high vacuumwith operating parameters as follows: 10.5mm sample working distance, 15-keV beam accelerating voltage, 4.0 beam spot size, 900 seconds live time.
Repository and institutional abbreviation.—Specimens used in this study are reposited at the Royal Ontario Museum (ROM).
Remarks.—The radially symmetrical thallus architecture of Wiartonella, comprising a central axis bearing laterals arranged in discrete whorls, is a common characteristic of dasycladalean algae, an extant order within the Chlorophyta that develops cm-scale unicellular (siphonous) thalli. Outwardly similar thalli, however, are also produced by charophytes (see Feist et al., 2003), as well as by some red and brown algae, all of which are multicellular. It is not possible to determine from the specimens if Wiartonella thalli were siphonous, but details of the ontoge- netic sequence, particularly the shedding of higher-order lateral segments (see below), point strongly to a dasycladalean affinity. However, because nothing is known for this taxon regarding chlorophyll composition or cellular-level organization, the possibility remains that Wiartonella belongs to a group of algae apart from Dasycladales for which there are no living representatives.
Wiartonella nodifera new species Figures 1.1, 1.2, 2.1–2.3, 3.1–3.14, 4.1–4.4
Holotype.—ROM 63795 (Fig. 3.3, 3.4), Silurian, Eramosa Formation exposed in the northernmost pit of the Owen Sound Ledgerock Ltd. quarry, 4 km northwest of Wiarton, Ontario.
Diagnosis.—Noncalcified cylindrical to claviform thallus comprising a narrow, cylindrical, uniaxial, unbranched main axis with laterals in whorls (euspondyl). Laterals along lower part of thallus unbranched, hairlike. Laterals along upper part of thallus branched to the second order; first-order lateral segments cylindrical along most of length but with expanded termina- tions; second-order lateral segments produced in pairs from tips of first-order segments, long, slender, distally-tapered. Rhizoid short, stout.
Occurrence.—Known only from the type locality.
Description.—Thallus noncalcified, typically 3 to 6mmwide and reaching 45mmin height (ROM63801.1; Fig. 1.1), comprising a
3
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
