Leiming Yin

Doushantuo embryos preserved inside diapause egg cysts

Phosphatized microfossils in the Ediacaran (635–542 Myr ago) Doushantuo Formation, south China, have been interpreted as the embryos of early animals. Despite experimental demonstration that embryos can be preserved, microstructural evidence that the Doushantuo remains are embryonic and an unambiguous record of fossil embryos in Lower Cambrian rocks, questions about the phylogenetic relationships of these fossils remain. Most recently, some researchers have proposed that Doushantuo microfossils may be giant sulphur-oxidizing bacteria comparable to extant Thiomargarita sp. Here we report new observations that provide a test of the bacterial hypothesis. The discovery of embryo-like Doushantuo fossils inside large, highly ornamented organic vesicles (acritarchs) indicates that these organisms were eukaryotic, and most probably early cleavage stage embryos preserved within diapause egg cysts. Large acanthomorphic microfossils of the type observed to contain fossil embryos first appear in rocks just above a 632.5 ± 0.5-Myr-old ash bed, suggesting that at least stem-group animals inhabited shallow seas in the immediate aftermath of global Neoproterozoic glaciation.

Neoproterozoic Fossils in Mesoproterozoic Rocks? Chemostratigraphic Resolution of a Biostratigraphic Conundrum from the North China Platform

Abstract Siliciclastic rocks of the Ruyang Group, southern Shanxi, and the broadly equivalent Gaoshanhe Group, Shaanxi, contain exceptionally well-preserved, large (O ≈ 150 μm) acanthomorphic acritarchs recently interpreted as late Neoproterozoic (Sinian, c. 800-544 Ma) in age. This biostratigraphic interpretation is based on the presence of large acanthomorphs in Sinian successions of South China and elsewhere and the perceived absence of comparable forms in older rocks; it casts doubt on the long-accepted interpretation of Ruyang and correlative rocks as Mesoproterozoic in age (1600-1000 Ma). In contrast, thick marine dolomites in overlying units contain abundant radial fibrous fabrics and a narrow range of δ13C values (c. 0 ± 1‰ vs. PDB), features which characterize unambiguously Mesoproterozoic carbonates elsewhere on the North China Platform and on other continents. Age estimates based on petrofabrics and chemostratigraphy are corroborated by a UPb zircon age of 999 Ma (no recorded error) for granites which intrude overlying carbonates. Thus, in combination, the available data constrain the Ruyang siliciclastics and overlying carbonates to be older than about one billion years, making Shuiyousphaeridium Yan and other large process-bearing acritarchs from these units among the oldest known distinctly ornamented eukaryotic microfossils.

Pyritized chuarids with excystment structures from the late Neoproterozoic Lantian formation in Anhui, South China

We report an unusual instance of macrofossil pyritization in the Precambrian: three-dimensionally pyritized internal molds of chuarids from the late Neoproterozoic Lantian formation (∼550–600 Ma) in southern Anhui Province, South China. These chuarid internal molds are composed almost entirely of iron oxide pseudomorphs after pyrite framboids (5–20 μm in diameter) and polyhedra (1–2 μm in diameter); pyritization probably occurred near the water–sediment interface during authigenesis. The internal molds are typically enveloped by a diagenetic quartz rim. Furthermore, about half of the Lantian chuarid population display medial split excystment structures, suggesting that the Lantian chuarids are eukaryotic megacysts rather than colonial prokaryotes. Applying a similar megacyst interpretation to other Proterozoic chuarid populations may not be straightforward, largely because of the lack of diagnostic features in most chuarids. Chuarids (in particular those in sole Chuaria assemblages) may therefore represent a polyphyletic group of diverse eukaryotic (and perhaps prokaryotic) origins, although the Chuaria–Tawuia association may represent a biologically and biostratigraphically coherent group.

The oldest known dinoflagellates: Morphological and molecular evidence from Mesoproterozoic rocks at Yongji, Shanxi Province

Abundant and well-preserved organic-walled microfossils including acanthomorphic acritarchs have been found in Mesoproterozoic Beidajian Formation in the Yongji area of Shanxi Province, North China. The morphological and ultrastructural features of these acanthomorphic acritarchs resemble living dinoflagellates (e.g. double-walled and polygonal structures), which leads to the interpretation of these fossils as probably the oldest dinoflagellates. The detection of dinosterane, a dinoflagellate biomarker, from pyrolytic product of these fossils further supports the morphological inference. This finding is consistent with molecular clock estimate that dinoflagellates may have diverged 700 to 900 million years (Ma) before previously known fossil record.

New observations on spicule- like structures from Dou- shantuo phosphorites at Weng'an, Guizhou Province

Doushantuo phosphorites at Weng’an, Guizhou Province, provide a unique opportunity for the study of early evolution of multicellular organisms, including metazoans. Our light microscope and SEM observations, however, do not substantiate a sponge spicule interpretation of spicular structures. No convincing axial canals have been seen in the observed spicule population. Instead, the coexistence of some monaxonal spicules with clearly diagenetic crystal fascicles and dumbbells suggest that these monaxons may also be diagenetic in origin. Our preliminary EDS analyses detect no significant silicon in spicule-containing intraclasts (including abiotic clasts and fragments of sphaeromorphic acritarchs and algal thalli), that contain abundant monaxonal spicular structures. We, therefore, believe that the evidence for a sponge spicule interpretation of the Doushantuo spicular structures are at best ambiguous at present; these alleged sponge spicules are indistinguishable from coexistent diagenetic crystals.

MICROBIOTA FROM THE NEOPROTEROZOIC LIULAOBEI FORMATION IN THE HUAINAN REGION, NORTHERN ANHUI, CHINA

Abundant and well-preserved acritarchs have been obtained from shales of the Neoproterozoic Liulaobei Formation in the Huainan region, northern Anhui Province, China. This microfossil assemblage, consisting of 9 genera, 11 species and an undetermined form, is dominated by sphaeromorphic acritarchs, as well as filamentous cyanobacteria. With the exception of a few new forms, e.g., Pololeptus rugosa (Yin, C.Y.) comb. nov., P. biacris (Yin, C.Y.) comb. nov. and the undetermined taxon, most components of this microbiota are well known from Neoproterozoic deposits elsewhere in the world. An integrational assessment of this microbiota in conjunction with the accompanying occurrence of the Chuaria-Tawuia megafossil assemblage, as well as radiometric datings, tends to suggest that the Liulaobei Formation might be bracketed within a Late Riphean time range of ∼850-700 Ma, providing an useful reference for estimating the age of the overlying Jiuliqiao Formation, which yields carbonaceous worm-like fossils probably of a metazoan origin.

Discovery of Ordovician acritarchs in Buqingshan ophiolite complex, East Kunlun Mountains and its significance

This note reports the first discovery of Middle-Late Ordovician acritarchs from the Buqingshan ophiolite complex of the southern ophiolite zone of East Kunlun. The acritarch assemblage is dominated with acanthomorphids (approx. 32%) and sphaeromorphds (approx. 63%) and contains more characteristic forms, such asLophosphaeridium edenense, L. varum, Nothooidium sp.,?Buedingiisphaaeridium sp.,Visbysphaera sp.,Strophomorpha sp., etc. In addition, some tube-like fragments and tetrads, which are recognized as affinity to terrestrial plants and usual occurrence in Late Ordovician-Early Silurian strata, are preserved together with acritarchs. All the known fossil evidence indicates that the strata should be Middle-Late Ordovician in age. It not only provides paleontological proof for the existence of Ordovician ophiolite, but also challenges the usual ideas on strata composition of the studied area and the southern ophiolite zone of East Kunlun, and the models on tectonic framework and evolution of this area and the northern part of the Qinghai-Tibetan Plateau.

A kind of coccoid dinoflagellates-like fossils gives a new explanation of source of dinosterane in the Early-Middle Cambrian

The coccoid fossils covered with thick gelatinous envelop containing several gametes are discovered in gyps and salt deposits of Cambrian, H4well and chert bed of the base of Yuertus Formation (∈11) of Xiaoerbulake Section. The fossils are described and compared with coccoid dinoflagellates. These fossils may be a coccoid life-cycle stage (vegetative cyst) of coccoid dinoflagellates. If this identification is correct, the coccoid dinoflagellates-like fossils could give a reasonable explanation of the dinoflagellate-specific biomarkers from Cambrian, H4 well, Tarim Basin.

Nano-Scale Spheroids and Fossils from the Ediacaran Doushantuo Formation in China

Exceptionally preserved nano-scale spheroids derived from microbial processes and nano-scale fossils have been discovered from the black shales of the Jijiawan section of the Ediacaran Doushantuo Formation in the Yangtze Gorge area of Hubei Province, southern China. The numerous soccer ball-like spheroids are pyritized. Their morphology and abundant preservation may suggest that they could possibly be related to larger spheroids, regardless of the tremendous dimensional gap found in the phosphorite and cherts of the Doushantuo Formation, including those recognized as ‘embryos’. The colony-like spheroids preserved in situ and obtained by acid maceration are compared with known Neoproterozoic microfossils—Bavlinella faveolata (or Sphaerocongregus variabilis). Additionally, nano-scale fossil bodies, characterized by morphological features comparable to living cyanobacteria, fungi and possible unicellular heterotrophic protists were observed in different minor laminae of the black shale samples. This study aims to reveal the aspects of nano-scale biota preserved in the black shale of the Ediacaran Doushantuo Formation, and highlight the taphonomy of microorganisms during the key transition from the anoxic deeper oceans to the oxygenated oceans of the early Ediacaran interval.

Comparison between cryptospores from the Cambrian Log Cabin Member, Pioche Shale, Nevada, USA and similar specimens from the Cambrian Kaili Formation, Guizhou, China

Abundant cryptospore-like microfossils have been collected from a sample of the “Middle” Cambrian Log Cabin Member of the Pioche Shale in eastern Nevada, USA. Compared with organic-walled microfossils obtained from the Cambrian Kaili Formation in eastern Guizhou Province, China, some specimens of leiosphers may be inferred to be similar cryptospore-like microfossils. The new fossil record would be the oldest known specimens of cryptospore-like microfossils during the Cambrian Period.