New Bivalved Arthropods from the Cambrian(Series 3, Drumian Stage) of Western Hunan, South China

We report two new three-dimensionally phosphatized microfossils, Cambrolongispina reticulata gen. et sp. nov. and Cambrolongispina glabra gen. et sp. nov., from the middle Cambrian （Series 3, Drumian Stage） at Wangcun, Yongshun County, western Hunan, South China. They are bivalved arthropods, with thin, pliable, originally chitinous or chitin-calcareous shields （c. 350-517 I1 m long）. The shields are equipped with a pair of antero-dorsal spines. The spines are internally hollow, varying in length from 1/2 of to as long as the shield length in C. reticulata, and uniformly longer than the shield length in C. glabra. The spines of C. reticulata are ornamented with a longitudinal row of conical or blade-shaped denticles along the posterior edge. Cambrolongispina lacks marginal rims, valve lobation and sulci which are diagnostic of the Bradoriida sensu stricto. It also lacks a donblure/duplicature characteristic of phosphatocopids and some bradoriids. It could be related to the Monasteriidae （which may belong to Bradoriida sensu lato）, both characterized by a pair of antero-dorsal spines. Cambrolongispina may have been meiofaunai detritus feeders that lived on or within sediments. The antero-dorsal spines may have been sensory organs to detect nearby predators. The posterior denticles on these spines might have facilitated the sensory function of the spines.

Early Diagenetic Dolomite as a Potential Archive of Paleoredox Fluctuations in an Early Tonian Marine Basin?

The Tonian Period witnessed important environmental changes and critical evolutionary innovations. Published iron speciation data suggest a global redox transition of mid-depth seawaters from euxinic to ferruginous in early Tonian, but details of this transition remain unknown. This study explores Tonian stromatolitic carbonates as a possible archive of paleoenvironmental changes, through the investigation of dolomitic limestones and dolostones associated with stromatolites of the Weiji Formation in the Huaibei region of North China. Three types of dolomitization are recognized on the basis of petrographic and geochemical data. Type Ⅰ and Ⅱ dolomitization resulted in dolomitic limestones characterized by LREE depletions, MREE enrichments, positive yttrium anomalies, and a lack of europium anomalies, indicating early diagenetic dolomitization, possibly in the iron reduction zone and under the influence of bottom seawater. The lack of cerium anomalies in these carbonates suggests anoxia in shallow marine environments. The coexistence of ferroan/non-ferroan dolomite crystals and overgrowth bands is interpreted as possible evidence for rapid fluctuations between iron-rich and iron-depleted conditions in pore-waters or seawaters. In contrast, type Ⅲdolomitization resulted in pervasively dolomitized stromatolitic carbonates and likely represents late diagenetic processes. This study highlights the potential of early diagenetic dolomite as an archive for paleoenvironmental investigations.

Extinctions,Morphological Gaps,Major Transitions,Stem Groups,and the Origin of Major Clades,with a Focus on Early Animals

Systematic extinctions can leave major morphological gaps between living crown-group clades.Such morphological gaps would be perceived,from a neontological point of view,as major evolutionary transitions.In order to fill these morphological gaps and to map the evolutionary steps toward major evolutionary transitions,we need to integrate extinct stem-group taxa in phylogenetic studies.However,the recognition of stem group has not been widely adopted in the study of early animal fossils,despite that all fossils are stem groups at one level or another.Part of the difficulty is that stem groups may not have all features that collectively diagnose the respective crown group,and they can have unique(autapomorphic)features,making them tantalizingly similar to and frustratingly different from the crown group(e.g.,stemgroup eukaryotes can be prokaryotic and stem-group animals can be protistan).The need to embrace stem groups and to implement the PhyloCode,in order to achieve phylogenetic clarity and to offer key paleontological insights into the origin and early animal evolution,is illustrated in debates on several controversial Ediacaran and Cambrian fossils.

Rare earth elements and carbon isotope geochemistry of the Doushantuo Formation in South China:Implication for middle Ediacaran shallow marine redox conditions

The middle Ediacaran Shuram excursion, the largest negative δ 13 C carb excursion in Earth history, has been interpreted as indirect evidence for episodic oxidation and remineralization of deep ocean DOC (dissolved organic carbon). It has been hypothesized that such oxidation event may have occurred when anoxic DOC-laden deep water was brought to shallow shelves during oceanic upwelling, which is expected to cause localized anoxia in shallow environments. To test this prediction, we systematically analyzed rare earth elements (REE) and δ 13 C carb of the upper Doushantuo Formation carbonates in the Yangtze Gorges area of South China, which were deposited in an inner shelf environment and record a large negative δ 13 C carb excursion correlated to the Shuram event. The REE data show a significant positive shift in Ce/Ce* values, synchronous with a pronounced negative δ 13 C carb shift. This positive Ce/Ce* shift is interpreted to represent an oceanic anoxia event in shallow shelf environments, which may have been caused by the upwelling or impingement of oxygen-depleted and 12 C-enriched deep water onto shelves. This anoxia event coincides with a sharp decline in the abundance and diversity of Ediacaran acanthomorphic acritarchs, raising the possibility that these two geobiological events may be causally related.

Phosphatized biotas from the Neoproterozoic Doushantuo Formation on the Yangtze Platform

The Doushantuo Formation in South China was deposited after the Nantuo glaciation but before the evolution of complex Ediacaran metazoans. It contains multiple taphonomic windows, in its cherts, carbonaceous shales, and phosphorites, onto the late Neoproterozoic biosphere. The phosphatic window is unusually clear; Doushantuo phosphorites at Weng’an (Guizhou Province) are known to exquisitely preserve a multitude of single-celled eukaryotes, muiticellular algae, and microscopic animals. Our recent survey reveals that, in addition to the now famous Weng’an locality, Doushantuo phosphorites at Baokang (Hubei), Chadian (Shaanxi), and Shangrao (Jiangxi) also contain diverse eukaryotes preserved at the cellular level. All these phosphorites were deposited in shallow-water environments, typically above fair weather wave base and close to ancient islands. Along with Doushantuo cherts and shales, these phosphorites give us a clearer and more complete picture of late Neoproterozoic biological evolution: there

The Lantian biota:A new window onto the origin and early evolution of multicellular organisms

The Lantian biota at the Lantian Town of Xiuning County,Anhui Province,is preserved in black shales of the Ediacaran Lantian Formation.It yields some of the oldest known complex macroorganisms,including fan-shaped seaweeds and possible animal fossils with tentacles and intestinal-like structures reminiscent of modern coelenterates and bilaterians.The Lantian Lagerst tte sheds new light on the origin and early evolution of multicellular organisms in relatively quiet and deep environments soon after the Neoproterozoic Marinoan glaciation.The morphological complexity and diversity of early multicellular organisms may be closely related to sexual reproduction and alternation of generations.The fluctuation of oceanic redox conditions during this period may have played a role in the ecology and preservation of the Lantian biota.

The earliest Foraminifera from southern Shaanxi,China

Vase-shaped microfossils(VSMs) described herein mainly occur as isolated individuals in thin bedded siltstone and silty carbonate of the Gaojiashan Member of the upper Ediacaran Dengying Formation(ca.551-541 Ma).Although these fossils are abundant,chained tests or other types of colonial aggregates have not been observed.Specimens in the siltstones can easily be isolated from the host rocks by ultrasonic vibrators.Compared with the co-occurring fossils Gaojiashania and Conotubus,VSMs are rarely pyritized,yet they are always three-dimensionally persevered with little deformation,suggesting that their tests were sturdy and possibly mineralized.Petrological observation and elemental mapping reveal two types of tests that are respectively calcareous and siliceous in composition.Calcareous tests typically consist of two to three crypto-crystal laminae,somewhat resembling bilamellar walls of foraminifers.Siliceous tests consist of fine-grained particles agglutinated with siliceous cement,similar to agglutinated walls of foraminifers.The Gaojiashan VSMs are broadly similar,at least in gross morphology,to the testate amoebae-like VSMs,but their relative large sizes(600-2400 μm) and possibly mineralized(rather than organic) tests argue against this comparison.They also show some similarities to other protozoans,especially tintinnids.However,tintinnids have robust pesudochitinous loricae consisting of both secreted and agglutinated materials.Moreover,tintinnid loricae differ in shape from the Gaojiashan VSM tests in having a constricted aboral end(sometimes with a caudal appendix) and a flaring oral opening.If the Gaojiashan VSMs are indeed related to foraminifers,they indicate that foraminifers were important players in late Ediacaran communities.