Journal of Paleontology, 91(3), 2017, p. 434–443 Copyright © 2017, The Paleontological Society 0022-3360/15/0088-0906 doi: 10.1017/jpa.2016.161
Costinuculana magharensis n. gen. n. sp. (Bivalvia, Nuculanidae) from the Middle Jurassic of Gebel Maghara, North Sinai, Egypt
Wagih S. Ayoub-Hannaa,1,2 Ahmad A. Abdelhady,3 and Franz T. Fürsich2
1Geology Department, Faculty of Science, Minufiya University, El-Minufiya, Shibin El Kom, Egypt ⟨
wagih_hannaa@yahoo.com⟩ 2FG Paläoumwelt, Geozentrum Nordbayern der Friedrich-Alexander Universität Erlangen-Nürnberg, Loewenichstrasse 28, D-91054 Erlangen,
Germany ⟨
franz.fuersich@fau.de⟩ 3Geology Department, Faculty of Science, Minia University, 61519 Minia, Egypt ⟨
alhady2003@yahoo.com⟩
Abstract.—The nuculanid bivalve Costinuculana magharensis new genus new species is described from the middle to upper Bathonian Kehailia Formation of Gebel Maghara, North Sinai, Egypt. Costinuculana differs from other genera of the family Nuculanidae by the presence of opisthocline ribs along the rostrum. These ribs are variable in shape and size, straight to folded posteriorly, bifurcate ventrally and occasionally postero-dorsally, and cover an area ~45% of the total valve length from the posterior end. The life position of C. magharensis n. gen. n. sp. is reconstructed on the basis of a functional interpretation of its morphology and by comparison with closely related Recent forms. The asymmetrical commarginal ribs facilitated the burrowing process. The posterior oblique ribs are asymmetrical in cross-section with a steeply concave side in the burrowing direction and slightly convex side in the opposite direction. They probably kept the bivalve in a stable position once the desired depth had been reached. The thick oblique ribs probably also increased the strength of the rostrum and offered resistance against durophagous predators, being presumably partly exposed above the sediment-water interface. Based on the associated fauna, Costinuculana n. gen. lived in a low-energy environment characterized by a fine-grained, soft substrate.
Introduction
Gebel Maghara is a dome-like structure covering ~400km2 in the northern Sinai, 50 km south of the Mediterranean coast (Fig. 1). It comprises the thickest and most complete Jurassic outcrop in northern Sinai (1800 m; Al Far, 1966; Keeley, 1994). The Middle–Upper Jurassic succession of Gebel Maghara is well known for its rich and diverse macrobenthic fauna such as brachiopods, bivalves, gastropods, ammonites, and corals. This fauna has been repeatedly studied from a taxonomic point of view (e.g., brachiopods: Farag, 1957, 1959; Farag and Gatinaud, 1960a, b; Feldman, 1987; Hegab, 1989, 1991; Feldman et al., 1991, 2012; bivalves and gastropods: Douvillé, 1916, 1925; Hirsch, 1980; and ammonites: Arkell et al., 1952; Parnes, 1988). The most-recent studies dealing with the strati- graphy and paleoecology are given by Abdelhady (2014) and Abdelhady and Fürsich (2014, 2015a, b, c). The purpose of this paper is: (1) to describe the new bivalve
taxon Costinuculana magharensis n. gen. n. sp. (order Nuculanida) from the Bathonian of Gebel Maghara and to compare it with similar taxa of the family Nuculidae; (2) to interpret the function of its oblique ribs, which cover an area up to ~45% of total valve length from the posterior end and to reconstruct its autecology; and (3) to determine its paleo- environmental setting on the basis of facies relationships and associated faunal elements.
Geologic setting
The Jurassic succession of GebelMaghara represents a sequential development of continental and marine sediments, starting in the Early Jurassic (Toarcian) and lasting until the Kimmeridgian (Fig. 2). It represents a wide variety of continental, deltaic, nearshore-siliciclastic, and carbonate-shelf environments (Al Far, 1966; Picard and Hirsch, 1987), and contains a rich macrofauna. The marine strata are represented by the Rajabiah, Bir Maghara, and Masajid formations, whereas the continental sediments include the Mashabba, Shusha, and Safa formations. The nuculanid specimens have been collected from the middle to upper Bathonian Kehailia Formation (Fig. 2). This formation represents the lower member of Al Far’s(1966)Masajid Forma- tion (Kehailia Member). The Kehailia Formation unconformably overlies the lower Bathonian Safa Formation and underlies the Callovian Arousiah Formation (Fig. 2). It consists of yellow, highly fossiliferous marly silts and marls with thin, yellow glauconitic limestone intercalations and occasional sandstone interbeds. For more details about litho- and biostratigraphy see Abdelhady (2014) and Abdelhady and Fürsich (2015a, b, c).
Materials and methods
The present study is based on 10 specimens with preserved shells that were collected from the middle to upper Bathonian
434
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