Melchin et al.—Llandovery retiolitine graptolites from Arctic Canada
attached to transverse rods by connecting rods. Ancora sleeve of very largemeshes, better developed on reverse side, seams facing out. No evidence of the presence of stomata. List surfaces smooth to very finely striated.
Etymology.—cancellatus: L; cross-barred, lattice; referring to basket-like ancora umbrella.
Remarks.—See remarks for genus and for Aeroretiolites? sp.
Aeroretiolites? sp. Figure 14.6–14.8
Materials.—One very well-preserved, mature specimen with a complete ancora umbrella.
Occurrence.—L. convolutus Zone from Cape Manning, Corn- wallis Island.
Description.—Tubarium of five thecal pairs, widening gradually from 1.2mm across ancora umbrella to a maximum of 1.88mm distally. 2TRD 1.75–2.0mm. Prosicula not preserved, prosicular interval and virgella ~1.2mm long. Ancora umbrella simple and very shallow, with four radial lists, saucer shaped, with an irregular rim. Mid-ventral lists moderately inclined, slightly convex. Mid-ventral list of theca 11 attached to rim of umbrella; distal mid-ventral lists relatively long, slightly convex. Ventral side orifice present under theca 12, none under theca 11. Thecal lateral apertural rods and looping apertural rim horizontal. Nema attached by connecting rods to transverse rods. Zigzag lists define reverse wall. Pleural lists connected to each other directly at lateral apertural rods, and are parallel to each other on both lateral walls. No ancora sleeve. List surfaces smooth to very finely striated.
Remarks.—Aeroretiolites? sp. is a represented by only a single, very well-preserved specimen that is similar in most respects to Aeroretiolites
cancellatus.Itdiffers,however,inits possessionof a simpler and shallower ancora umbrella without spiral lists, pleural lists that are straight, vertical and continuously connected, and thecal apertural rims that are horizontal. In addition, the single specimen shows no prosicula or ancora sleeve lists, although these features are sometimes inconsistently preserved in some retiolitines. Considering that there is only a single specimen, we identify it as Aeroretiolites?sp. The specimen of Aeroretiolites? sp. appears similar in
many respects to those of Eorograptus spirifer but differs in that the former possesses mid-ventral thecal lists and lacks spiral lists on the ancora.
Genus Paraplectograptus Příbyl, 1948
Type species.—Retiolites eiseli Manck, 1917, by original designation.
Paraplectograptus? sp. Figure 15.1–15.6
Materials.—Nine fragmentary, somewhat compressed speci- mens, all immature, of which five are well preserved, and most complete consists of ancora umbrella and up to three thecae.
Occurrence.—S. guerichi Zone, Snowblind Creek and Rookery Creek, Cornwallis Island. Three additional questionable specimens fromSnowblind Creek and one questionable specimen from the L. convolutus Zone at CapeManning.
Description.—Sicula 0.4–0.49mm long, virgella 0.6–0.7mm, prosicula partially to completely preserved, with longitudinal rods. Ancora umbrella simple, shallow, consisting of four radial lists that may divide distally, with complete, undulatory rim, 1.2–1.5mm wide. Openings under theca 1² about twice as large as that under theca 11. Transverse rods present. Pleural lists inclined slightly, connected to lateral apertural list declined strongly outwardly, and to horizontal apertural rim. Apertural lips looped, horizontal. No thecal mid-ventral lists. Nema attached to connecting rods. Zigzag lists on reverse side, outside of which are a few weak ancora sleeve lists; none observed on obverse side. List micro-ornament smooth or weakly longitudinally striated.
Remarks.—These specimens may represent a new species, possibly representing a new genus, but because of the limited number of distorted specimens, and their immaturity, they are questionably referred to the genus Paraplectograptus,with which they share a similar ancora umbrella and tubarium construction (see Bates et al., 2005, fig. 6F). Our phylogenetic analysis (see above) suggests that this is a stem taxon to the clade that includes Paraplectograptus, Sokolovograptus and all of the more derived species previously regarded as “plectograptines.” Paraplectograptus? sp. appears to con- sistently possess a preserved prosicula. Its micro-ornamentation consists of fine parallel striae, in contrast to the pustular ornamentation of Paraplectograptus s.s. and more derived “plectograptines.”
Acknowledgments
M.J.M and A.C.L. acknowledge the long-term financial support from Natural Sciences and Engineering Research Council (Canada) (NSERC), and logistical support from the Polar Continental Shelf Project. A.K. acknowledges a financial grant from Ministerstwo Nauki i Szkolnictwa Wyższego decision number 499/N (Poland) and collaborative support from NSERC 2009/0. Field support from A. McCracken, M. Coniglio, J. Lukasik, J. Russel-Houston, E. MacDonald, P. Noble,
Figure 15. Scanning electron microscopy images of Paraplectograptus?sp.:(1) GSC137657, stereopair of a slightly deformed immature specimen with well-preserved prosicula with weakly developed longitudinal rod, and one thecal pair, section LL1B, S. guerichi or S. turriculatus Zone; (2, 3) GSC137658, (2) proximo-lateral view of interior of simple ancora umbrella, (3) lateral view of moderately distorted specimen; section LL1B, S. guerichi or S. turriculatus Zone; (4, 6) GSC137659, (4) enlargement of ancora list showing weakly striated micro-ornament and fusellar insert seams, (6) shallow and simple ancora umbrella and remnant of prosicula, section LL1-77, S. guerichi or S. turriculatus Zone; (5) GSC 137660, stereopair of well-preserved specimen showing ancora umbrella, partially preserved prosicula, and the first thecal pair, pleural lists (a) and lateral apertural rods (b), sectionMSC07, 3m a above 01G, S. guerichi Zone?.
141
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
