【摘要】 河北省庞家堡长城系大红峪组下部的局部硅化的层状叠层石的基本层内原位保存着宽球藻目的一种真穿石蓝藻化石群体,化石的估计年龄为距今1700Ma。新发现的微化石被命名为Eohyella campbellii gen.et sp.nov.,与相邻的基本层中建造叠层石的球状蓝藻化石比较,穿石蓝藻细胞保存得极好,细胞结构只显出轻微的收缩变形。细胞群集沿着硅化的叠层石基本层的边缘分布以及群集基部向下伸出的假丝体表明新种具有穿石习性。它与向上生长的建造叠层石的Coniunctiophycus-Siphonophycus藻席化石群共生并互层,这表明两者是原地、同时的微生物化石群。这是迄今所知最早的真穿石微生物的化石纪录。更多还原

【Abstract】 A microbial population of euendolithic pleulocapsalean cyanophytes was found to be preserved in situ within the laminae of partially silicified stromatolites (Stratifera)in the lower part of the Early Proterozoic Dahongyu Formation, Changcheng Group(System)of Pangjiabao Iron Mine, Hebei Province, North China. The isotopic age of the Dahongyu Formation is between 1,650 Ma and 1,770 Ma, while the estimated age of the microfossils is ca. 1,700 Ma. The microfossil is described herein as a new taxon: Eohyella campbellii gen. et sp. nov. In contrast to the contemporaneous microfossils of stromatolite-building coccoid cyanophytes found in adjacent laminae, the cells of the endolith are remarkably well-preserved. The cellular structures show little shrinkage deformation and consist of brown, finely dispersed grains of kerogenous organic matter. The distribution pattern of cell aggregates along the upper edge of clear silicified horizons and the orientation of pseudofilaments downward reveal the endolithic habit of this new taxon. Alternation with upright oriented stromatolite-building Coniunctiophycus-Siphonophycus microfossil assemblage assures the autochthoneity and synchronicity of both fossil assemblages. This is thus far the earliest occurrence of euendolithic microorganism in the fossil record.SYSTEMATIC DESCRIPTIONPhylum CyanophytaClass CoccogoneaeOrder PleuroeapsalesFamily HyellaceaeEohyella gen.nov.Type species Eohyella campbellii gen. et sp. nov.Etymology Eos-(Gr.)——early, dawn; in reference to the modern euendolith genus Hyella Bornet and Flahault.Diagnosis Cells aggregated in colonies, arranged in pseudoparenchymatic groups from which pseudofilaments formed of single or multiple cell series project downward (in direction opposite to the stromatolite growth) and terminate with large droplet-shaped apical cells, variable in shape (spherical, polyhedral, semilunar, ellipsoidl) and size. Apical cells larger than others, characteristically elongated and dropshaped.Colonies occurring usually along the surface of silicified laminae and penetrating downward into these laminae. Individual cells commongly surrounded by hyaline clearance rather than enclosed with an envelope(Pl. Ⅰ, fig. 4; P1. Ⅱ, fig. 2 ). Dark cell envelopes visible only in the upper (presumed original surface) portion of the thalli (Pl. Ⅱ, figs. 1, 6).These "upper" cells are often smaller and seen in the process of division, and are presumed to be reproductive cells or gonidia. Clusters of such cells surrounded by a common envelope are interpreted as gonidangia.The new genus differs from Paleopleurocapsa Knoll et al. in its downward orientation of pseudofilaments and differentiation of apical cells.Eohyella campbellii gen. et sp. nov. (P1. Ⅰ, figs. 1—8; P1. Ⅱ, figs. 1—6; P1. Ⅲ, figs. 1—6)Etymology In honor of the American biologist Susan E. Campbell, who made significant contributions to the study of modern and fossil endoliths.Type specimen Holotype in thin section no. BGPZD-9B-8201, deposited in the collection of the Palaeontological Section, Department of Geology, Beijing University, and illustrated in P1. Ⅰ, figs. 1, 3 (iconotype) and 4, and P1. Ⅱ, figs. 1 and 3; with microscope stage coordinates as 19.3X/120.0Y, 20.8X/121.1Y and 20.5X/120.1Y (reference mark on the thin section 35.8X/127.7Y ).Type locality Lower strata of Dahongyu Formation, Changcheng Group (System), exposed in Pangjiabao Iron Mine, Hebei Province, about 125 km northwest of Beijing city.Diagnosis Same as for the genus. Four types of cells distinguished and measured separately: vegetative cells, apical cells, gonidangia and gonidia. Dimensions(length×width) of vegetative cells ranging from 2.6×1.9 to 18.2×4.0μm; mean and standard deviations of 92 cells measured, or±s(n): 6.6±2.37(92) in length and 3.5±1.12(92) in width; spherical cells±s(n): 4.9±1.14(29) in diameter, well aligned in the same range. Apical cells elongated, cylindrical to droplet-shaped with swollen distal end, 11.2×3.9 to 22.0×6.7μm, ±s(n): 15.4±4.12×5.1±1.36(6). Gonidangia slightly enlarged, 6更多还原