376
Journal of Paleontology 91(3):369–392 see arrow). In addition to these two main members, S. septatum
and S. kestron are occasionally present. In organic-poor layers, filaments grew upward. In contrast, filaments exhibit a horizontal growth tendency in organic-rich layers. Due to their interactive growth, characteristic rhythms of bright and dark layers were established.
Spherical colonies.—Spherical colonies are not very common in the new microbiota. They do not form a laminar plane because of their small scale. Colonially preserved spheres are generally small in size and have simple morphology. They are densely or sparsely distributed together and form small-scale
clusters in the matrix. According to their morphology and size, five species have been recognized and three species have been determined informally: Glenobotrydion varioforme, Coccos- tratus dispergens, Eosynechococcus moorei, Gloeodiniopsis sp., Coniunctiophycus majorinum, Tetraphycus gregalis, Clonophycus sp., and Myxococcoides sp. Colonially preserved coccoids are usually small in size and
simple in morphology. Inside the matrix, they are densely or loosely distributed together and formed some small-scale clusters. Gloeodiniopsis sp. (Fig. 8), as one of the colonially preserved coccoids, is very well preserved and shows the reproduction procedure of straight splitting (Fig. 8.3). Colonies with regular spherical outlines are typical elements (Fig. 9.3–9.8). Inside the spherical colony, tens or hundreds of cells are arranged densely with or without order. These colonies are comparable with some member of modern cyanobacteria Pleurocapsa and Gloeocapsa, which can lead to the process of multiple fissions and produce baeocytes.
Figure 5. Diameter-frequency distributions of Siphonophycus:(1) total diameter-frequency distribution of all Siphonophycus;(2) diameter-frequency distribution of three different Siphonophycus aggregates.
bundles, which may indicate that they were affected by water flow during their growth.
The second Siphonophycus aggregate is composed of
S. robustum and S. septatum, which are common elements and usually appear together to form small aggregates (Fig. 5.2, aggregate 2; Fig. 6.3, 6.4). These aggregates usually occur within organic-poor matrix, such as cements between pelletoids (Fig. 6.3, 6.4). They sometimes grew along with the outer edge of a pelletoid (Fig. 6.3). Their distribution pattern does not exhibit a particular direction of growth, but exhibits a chaotic state. This phenomenon may suggest that they were non- photosynthetic organisms, while indicating that they lived in a hydrostatic environment without sunshine. The third Siphonophycus aggregate is dominated by
S. typicum, which is the most abundant mat builder in the newly studied Dahongyu microbiota (Fig. 5.2, aggregate 3; Fig. 6.5). In S. typicum-dominated aggregates, S. robustum is an associated member and participated in mat-building (Fig. 6.5,
Isolated individuals.—In the Dahongyu microbiota, isolated individuals constitute up to 20% of the content and contribute to more than half of the diversity. Based on their morphology, we recognized five species, five undetermined species, and seven undetermined forms: Myxococcoides grandis, Xiaohongyuia sinica Shi and Feng n. gen. n. sp., Dictyosphaera macro- reticulta,
Asperatopsophosphaera umishanensis, Leio-
sphaeridia minutissima, Myxococcoides sp., Leioarachnitum sp., Leiosphaeridia sp., Pterospermopsimorpha sp., and seven problematic taxa. These isolated individuals mostly are coccoidal in
morphology, accompanied with fusiform microfossils and some irregular morphological microfossils. Spherical types are mostly smooth-surfaced, although ornamented spheres, such as granular-surfaced (Fig. 10.6–10.9) and reticular-surfaced (Fig. 10.10, 10.11) forms are also very common. Besides ornaments, other morphological features, such as longitudinal rupture (Fig. 11.1–11.7), neck-like extension (Fig. 11.8), spine-like structure (Fig. 11.12), vase-shaped morphology (Fig. 11.13), spines (Fig. 11.14, 11.15), and undefined shapes (Fig. 12), also suggest that they belong to different taxa. The small fusiform microfossil Leioarachnitum sp. has been recovered from the Dahongyu Formation in abundance
Figure 6. Filaments of Siphonophycus:(1) aggregate of S. thulenema, arrow indicates S. septatum: 2012XHYD_47_5; (2) aggregate of S. thulenema: 2012XHYD_47_5; (3) aggregate dominated by S. septatum and S. robustum: 2012XHYD_20_3; (4) aggregate dominated by S. septatum and S. robustum: 2008XHYD_2_1; (5) aggregate dominated by S. typicum, arrow indicates S. robustum: 2012XHYD_47_5. Scale bars are (1)15 μm, (2)10 μm, (3)60 μm, (4)50 μm, and (5)35 μm.
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