An early Cambrian euarthropod with radiodont-like raptorial appendages.

Resolving the early evolution of euarthropods is one of the most challenging problems in metazoan evolution1,2. Exceptionally preserved fossils from the Cambrian period have contributed important palaeontological data to deciphering this evolutionary process3,4. Phylogenetic studies have resolved Radiodonta (also known as anomalocaridids) as the closest group to all euarthropods that have frontalmost appendages on the second head segment (Deuteropoda)5-9. However, the interrelationships among major Cambrian euarthropod groups remain disputed1,2,4,7, which impedes our understanding of the evolutionary gap between Radiodonta and Deuteropoda. Here we describe Kylinxia zhangi gen. et. sp. nov., a euarthropod from the early Cambrian Chengjiang biota of China. Kylinxia possesses not only deuteropod characteristics such as a fused head shield, a fully arthrodized trunk and jointed endopodites, but also five eyes (as in Opabinia) as well as radiodont-like raptorial frontalmost appendages. Our phylogenetic reconstruction recovers Kylinxia as a transitional taxon that bridges Radiodonta and Deuteropoda. The most basal deuteropods are retrieved as a paraphyletic lineage that features plesiomorphic raptorial frontalmost appendages and includes Kylinxia, megacheirans, panchelicerates, 'great-appendage' bivalved euarthropods and isoxyids. This phylogenetic topology supports the idea that the radiodont and megacheiran frontalmost appendages are homologous, that the chelicerae of Chelicerata originated from megacheiran great appendages and that the sensorial antennae in Mandibulata derived from ancestral raptorial forms. Kylinxia thus provides important insights into the phylogenetic relationships among early euarthropods, the evolutionary transformations and disparity of frontalmost appendages, and the origin of crucial evolutionary innovations in this clade.

Developmental biology of Spiralicellula and the Ediacaran origin of crown metazoans.

The early Ediacaran Weng'an biota (Doushantuo Formation, South China) provides a rare window onto the period of Earth history in which molecular timescales have inferred the initial phase of crown-metazoan diversification. Interpretation of the embryo-like fossils that dominate the biota remains contentious because they are morphologically simple and so difficult to constrain phylogenetically. Spiralicellula from the Weng'an biota is distinguished by spiral internal bodies, allied through development to Megasphaera or Helicoforamina and interpreted variously as metazoan embryos, encysting protists, or chlorophycean green algae. Here we show, using X-ray microtomography, that Spiralicellula has a single-layered outer envelope and no more than 32 internal cells, often preserving a nucleus and yolk granules. There is no correlation between the extent of spiral development and the number of component cells; rather, the spiral developed with each palintomic stage, associated with cell disaggregation and reorientation. Evidence for envelope thinning and cell loss was observed in all developmental stages, reflecting non-deterministic shedding of gametes or amoebae. The developmental biology of Spiralicellula is similar to Megasphaera and Helicoforamina, which otherwise exhibit more rounds of palintomy. We reject a crown-metazoan affinity for Spiralicellula and all other components of the Weng'an biota, diminishing the probability of crown-metazoan diversification before the early Ediacaran.

The Evolution Pathway of Ammonia-Oxidizing Archaea Shaped by Major Geological Events.

Primordial nitrification processes have been studied extensively using geochemical approaches, but the biological origination of nitrification remains unclear. Ammonia-oxidizing archaea (AOA) are widely distributed nitrifiers and implement the rate-limiting step in nitrification. They are hypothesized to have been important players in the global nitrogen cycle in Earth's early history. We performed systematic phylogenomic and marker gene analyses to elucidate the diversification timeline of AOA evolution. Our results suggested that the AOA ancestor experienced terrestrial geothermal environments at ∼1,165 Ma (1,928-880 Ma), and gradually evolved into mesophilic soil at ∼652 Ma (767-554 Ma) before diversifying into marine settings at ∼509 Ma (629-412 Ma) and later into shallow and deep oceans, respectively. Corroborated by geochemical evidence and modeling, the timing of key diversification nodes can be linked to the global magmatism and glaciation associated with the assembly and breakup of the supercontinent Rodinia, and the later oxygenation of the deep ocean. Results of this integrated study shed light on the geological forces that may have shaped the evolutionary pathways of the AOA, which played an important role in the ancient global nitrogen cycle.

Fossils from South China redefine the ancestral euarthropod body plan.

BACKGROUND: Early Cambrian Lagerstätten from China have greatly enriched our perspective on the early evolution of animals, particularly arthropods. However, recent studies have shown that many of these early fossil arthropods were more derived than previously thought, casting uncertainty on the ancestral euarthropod body plan. In addition, evidence from fossilized neural tissues conflicts with external morphology, in particular regarding the homology of the frontalmost appendage. RESULTS: Here we redescribe the multisegmented megacheirans Fortiforceps and Jianfengia and describe Sklerolibyon maomima gen. et sp. nov., which we place in Jianfengiidae, fam. nov. (in Megacheira, emended). We find that jianfengiids show high morphological diversity among megacheirans, both in trunk ornamentation and head anatomy, which encompasses from 2 to 4 post-frontal appendage pairs. These taxa are also characterized by elongate podomeres likely forming seven-segmented endopods, which were misinterpreted in their original descriptions. Plesiomorphic traits also clarify their connection with more ancestral taxa. The structure and position of the "great appendages" relative to likely sensory antero-medial protrusions, as well as the presence of optic peduncles and sclerites, point to an overall homology with the anterior head of radiodontans. This is confirmed by our Bayesian phylogeny, which places jianfengiids as the basalmost euarthropods, paraphyletic with other megacheirans, and in contiguity with isoxyids and radiodontans. CONCLUSIONS: Sklerolibyon and other jianfengiids expand the disparity of megacheirans and suggest that the common euarthropod ancestor possessed a remarkable phenotypic variability associated with the externalized cephalon, as well as endopods that were already heptopodomerous, which differs from previous hypotheses and observations. These animals also demonstrate that the frontalmost pair of arthrodized appendage is homologous between radiodontans and megacheirans, refuting the claim that the radiodontan frontal appendages evolved into the euarthropod labrum, and questioning its protocerebral identity. This evidence based on external anatomy now constitutes a solid benchmark upon which we should address issues of homology, with the help of carefully examined palaeoneurological data.

Evolution of the Cholesterol Biosynthesis Pathway in Animals.

Cholesterol plays essential roles in animal development and disease progression. Here, we characterize the evolutionary pattern of the canonical cholesterol biosynthesis pathway (CBP) in the animal kingdom using both genome-wide analyses and functional experiments. CBP genes in the basal metazoans were inherited from their last common eukaryotic ancestor and evolutionarily conserved for cholesterol biosynthesis. The genomes of both the basal metazoans and deuterostomes retain almost the full set of CBP genes, while Cnidaria and many protostomes have independently experienced multiple massive losses of CBP genes that might be due to the geologic events during the Ediacaran period, such as the appearance of an exogenous sterol supply and the frequent perturbation of ocean oxygenation. Meanwhile, the indispensable utilization processes of cholesterol potentially strengthened the maintenance of the complete set of CBP genes in vertebrates. These results strengthen both biotic and abiotic roles in the macroevolution of a biosynthesis pathway in animals.

Hyoliths with pedicles illuminate the origin of the brachiopod body plan.

Hyoliths are a taxonomically problematic group of Palaeozoic lophotrochozoans that are among the first shelly fossils to appear in the Cambrian period. On the basis of their distinctive exoskeleton, hyoliths have historically been classified as a separate phylum with possible affinities to the molluscs, sipunculans or lophophorates-but their precise phylogenetic position remains uncertain. Here, we describe a new orthothecide hyolith from the Chengjiang Lagerstätte (Cambrian Series 2 Stage 3), Pedunculotheca diania Sun, Zhao et Zhu gen. et sp. nov., which exhibits a non-mineralized attachment structure that strikingly resembles the brachiopod pedicle-the first report of a peduncular organ in hyoliths. This organ establishes a sessile, suspension feeding ecology for these orthothecides and-together with other characteristics (e.g. bilaterally symmetrical bivalve shell enclosing a filtration chamber and the differentiation of cardinal areas)-identifies hyoliths as stem-group brachiopods. Our phylogenetic analysis indicates that both hyoliths and crown brachiopods derived from a tommotiid grade, and that the pedicle has a single origin within the brachiopod total group.

Sponge grade body fossil with cellular resolution dating 60 Myr before the Cambrian.

An extraordinarily well preserved, 600-million-year (Myr)-old, three-dimensionally phosphatized fossil displaying multiple independent characters of modern adult sponges has been analyzed by SEM and synchrotron X-ray tomography. The fossilized animal (Eocyathispongia qiania gen. et sp. nov.) is slightly more than 1.2 mm wide and 1.1 mm tall, is composed of hundreds of thousands of cells, and has a gross structure consisting of three adjacent hollow tubes sharing a common base. The main tube is crowned with a large open funnel, and the others end in osculum-like openings to the exterior. The external surface is densely covered with flat tile-like cells closely resembling sponge pinacocytes, and this layer is punctuated with smaller pores. A dense patch of external structures that display the form of a lawn of sponge papillae has also survived. Within the main funnel, an area where features of the inner surface are preserved displays a regular pattern of uniform pits. Many of them are surrounded individually by distinct collars, mounted in a supporting reticulum. The possibility cannot be excluded that these pits are the remains of a field of choanocytes. The character set evinced by this specimen, ranging from general anatomy to cell type, uniquely indicates that this specimen is a fossil of probable poriferan affinity. So far, we have only this single specimen, and although its organized and complex cellular structure precludes any reasonable interpretation that its origin is abiogenic, confirmation that it is indeed a fossilized sponge will clearly require discovery of additional specimens.

Clinical and morphological features of collagen type III glomerulopathy: a report of nine cases from a single institution.

AIMS: We report nine Chinese patients with collagen type III glomerulopathy. METHODS AND RESULTS: Two males and seven females were studied, ranging in age from 21 to 67 years. Proteinuria and hypertension were the most common symptoms, with incidences of 88.9 and 77.8%, respectively. Two patients had abnormal renal function. Their histological appearances varied. Massive eosinophilic and weakly periodic acid-Schiff (PAS)-positive substances were deposited along the capillary loops and in the mesangial area in three cases, while others had thickened capillary walls with a chain-like structure or double-contour appearance of the PAS- and silver-stained sections. Immunofluorescence analysis showed the abundant deposition of collagen type III. Electron microscopy revealed massive scattered or bundle-shaped fibre-like materials in the subendothelial and mesangial areas. During follow-up, 44.4% of the patients suffered a doubling of serum creatinine. The level of serum creatinine at biopsy was an independent predictor of this doubled serum creatinine value. CONCLUSIONS: Collagen type III deposits in the subendothelial and mesangial areas. Some patients show global nodular lesions, while others show subtle changes only via PAS/silver staining. Proteinuria and hypertension are the most common symptoms, and the serum creatinine level at biopsy is an independent predictor of the doubling of serum creatinine during follow-up.

Clinical and morphological features of fibronectin glomerulopathy: a report of ten patients from a single institution.

AIMS: Fibronectin glomerulopathy is a rare glomerular disease caused by the progressive deposition of fibronectin. We report 10 Chinese patients with fibronectin glomerulopathy. METHODS: Renal biopsies were performed on all patients, and the clinical and pathological parameters for all patients were analyzed. RESULTS: There were 6 males and 4 females, with an average age of 29±8 years. One patient had a family history of renal disease, all patients presented with proteinuria, and 80% of them suffered nephrotic range proteinuria. No patient demonstrated gross hematuria. The levels of serum creatinine were elevated, and the eGFR was decreased in 5 patients. Renal biopsy revealed a lobulated glomerular tuft. Patients showed numerous periodic acid-Schiff-positive and fuchsinophilic deposits in the mesangial area and along the capillary loops. Immense levels of fibronectin were detected in the glomerulus after immunofluorescence analysis. An electron microscopy scan found numerous electron-dense deposits in the mesangial and subendothelial areas. Immune-electron microscopy confirmed that the deposits consisted of fibronectin. CONCLUSION: Nephrotic proteinuria and massive intraglomerular fibronectin deposits are the most significant features of fibronectin glomerulopathy.

1.63-billion-year-old multicellular eukaryotes from the Chuanlinggou Formation in North China.

Multicellularity is key to the functional and ecological success of the Eukarya, underpinning much of their modern diversity in both terrestrial and marine ecosystems. Despite the widespread occurrence of simple multicellular organisms among eukaryotes, when this innovation arose remains an open question. Here, we report cellularly preserved multicellular microfossils (Qingshania magnifica) from the ~1635-million-year-old Chuanlinggou Formation, North China. The fossils consist of large uniseriate, unbranched filaments with cell diameters up to 190 micrometers; spheroidal structures, possibly spores, occur within some cells. In combination with spectroscopic characteristics, the large size and morphological complexity of these fossils support their interpretation as eukaryotes, likely photosynthetic, based on comparisons with extant organisms. The occurrence of multicellular eukaryotes in Paleoproterozoic rocks not much younger than those containing the oldest unambiguous evidence of eukaryotes as a whole supports the hypothesis that simple multicellularity arose early in eukaryotic history, as much as a billion years before complex multicellular organisms diversified in the oceans.

Gene inversion led to the emergence of brackish archaeal heterotrophs in the aftermath of the Cryogenian Snowball Earth.

Land-ocean interactions greatly impact the evolution of coastal life on earth. However, the ancient geological forces and genetic mechanisms that shaped evolutionary adaptations and allowed microorganisms to inhabit coastal brackish waters remain largely unexplored. In this study, we infer the evolutionary trajectory of the ubiquitous heterotrophic archaea Poseidoniales (Marine Group II archaea) presently occurring across global aquatic habitats. Our results show that their brackish subgroups had a single origination, dated to over 600 million years ago, through the inversion of the magnesium transport gene corA that conferred osmotic-stress tolerance. The subsequent loss and gain of corA were followed by genome-wide adjustment, characterized by a general two-step mode of selection in microbial speciation. The coastal family of Poseidoniales showed a rapid increase in the evolutionary rate during and in the aftermath of the Cryogenian Snowball Earth (∼700 million years ago), possibly in response to the enhanced phosphorus supply and the rise of algae. Our study highlights the close interplay between genetic changes and ecosystem evolution that boosted microbial diversification in the Neoproterozoic continental margins, where the Cambrian explosion of animals soon followed.

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.

Response to Comments on "Ultrastructure reveals ancestral vertebrate pharyngeal skeleton in yunnanozoans".

He et al. dispute our anatomical interpretations on the structures of cellular chambers and microfibrils in yunnanozoan branchial arches and put forward alternative interpretations on these structures. Zhang and Pratt argue that the microfibrils we identified in yunnanozoans are more likely modern organic contamination. Here we provide additional evidence to support our interpretations and dismiss the alternative interpretations.

Ultrastructure reveals ancestral vertebrate pharyngeal skeleton in yunnanozoans.

Pharyngeal arches are a key innovation that likely contributed to the evolution of the jaws and braincase of vertebrates. It has long been hypothesized that the pharyngeal (branchial) arch evolved from an unjointed cartilaginous rod in vertebrate ancestors such as that in the nonvertebrate chordate amphioxus, but whether such ancestral anatomy existed remains unknown. The pharyngeal skeleton of controversial Cambrian animals called yunnanozoans may contain the oldest fossil evidence constraining the early evolution of the arches, yet its correlation with that of vertebrates is still disputed. By examining additional specimens in previously unexplored techniques (for example, x-ray microtomography, scanning and transmission electron microscopy, and energy dispersive spectrometry element mapping), we found evidence that yunnanozoan branchial arches consist of cellular cartilage with an extracellular matrix dominated by microfibrils, a feature hitherto considered specific to vertebrates. Our phylogenetic analysis provides further support that yunnanozoans are stem vertebrates.

Diverse and complex developmental mechanisms of early Ediacaran embryo-like fossils from the Weng'an Biota, southwest China.

The origin and early evolution of animal development remain among the many deep, unresolved problems in evolutionary biology. As a compelling case for the existence of pre-Cambrian animals, the Ediacaran embryo-like fossils (EELFs) from the Weng'an Biota (approx. 609 Myr old, Doushantuo Formation, South China) have great potential to cast light on the origin and early evolution of animal development. However, their biological implications can be fully realized only when their phylogenetic positions are correctly established, and unfortunately, this is the key problem under debate. As a significant feature of developmental biology, the cell division pattern (CDP) characterized by the dynamic spatial arrangement of cells and associated developmental mechanisms is critical to reassess these hypotheses and evaluate the diversity of the EELFs; however, their phylogenetic implications have not been fully realized. Additionally, the scarcity of fossil specimens representing late developmental stages with cell differentiation accounts for much of this debate too. Here, we reconstructed a large number of EELFs using submicron resolution X-ray tomographic microscopy and focused on the CDPs and associated developmental mechanisms as well as features of cell differentiation. Four types of CDPs and specimens with cell differentiation were identified. Contrary to the prevailing view, our results together with recent studies suggest that the diversity and complexity of developmental mechanisms documented by the EELFs are much higher than is often claimed. The diverse CDPs and associated development features including palintomic cleavage, maternal nutrition, asymmetric cell divisions, symmetry breaking, establishment of polarity or axis, spatial cell migration and differentiation constrain some, if not all, EELFs as total-group metazoans. This article is part of the theme issue 'The impact of Chinese palaeontology on evolutionary research'.

The middle Cambrian Linyi Lagerstätte from the North China Craton: a new window on Cambrian evolutionary fauna.

The rapid appearance of major animal groups and complex marine communities during the Cambrian explosion is recorded in large part in Burgess Shale-type lagerstätten. However, the restricted temporal and spatial distribution of known lagerstätten continues to hinder the formation of a comprehensive perspective on Cambrian evolutionary faunas. Here we describe the Linyi Lagerstätte (ca. 504 mya), a new Cambrian Miaolingian lagerstätte from the Zhangxia Formation in Shandong Province, North China. The Linyi Lagerstätte contains a variety of well-preserved soft-bodied fossils, among which the non-trilobite arthropods, particularly the mollisoniids and radiodonts, are the most important groups. The new assemblage is remarkable for its excellent preservation of arthropod limbs, eyes and guts, as well as for its close similarity in taxonomic composition to Laurentian lagerstätten. The distinctive Linyi Lagerstätte holds great promise for providing additional insights into the morphological disparity, community structure and paleogeographic range of marine faunas during the middle Cambrian (Miaolingian).

The tempo of Ediacaran evolution.

The rise of complex macroscopic life occurred during the Ediacaran Period, an interval that witnessed large-scale disturbances to biogeochemical systems. The current Ediacaran chronostratigraphic framework is of insufficient resolution to provide robust global correlation schemes or test hypotheses for the role of biogeochemical cycling in the evolution of complex life. Here, we present new radio-isotopic dates from Ediacaran strata that directly constrain key fossil assemblages and large-magnitude carbon cycle perturbations. These new dates and integrated global correlations demonstrate that late Ediacaran strata of South China are time transgressive and that the 575- to 550-Ma interval is marked by two large negative carbon isotope excursions: the Shuram and a younger one that ended ca. 550 Ma ago. These data calibrate the tempo of Ediacaran evolution characterized by intervals of tens of millions of years of increasing ecosystem complexity, interrupted by biological turnovers that coincide with large perturbations to the carbon cycle.

Developmental biology of Helicoforamina reveals holozoan affinity, cryptic diversity, and adaptation to heterogeneous environments in the early Ediacaran Weng'an biota (Doushantuo Formation, South China).

The exceptional fossil preservation of the early Ediacaran Weng'an biota provides a unique window on the interval of Earth history in which animal lineages emerged. It preserves a diversity of similarly ornamented encysted developmental stages previously interpreted as different developmental stages of one taxon. Although Helicoforamina wenganica is distinguished from other forms by a helical groove or canal, it has been interpreted as a developmental stage of cooccurring metazoan, nonmetazoan holozoan, or green algal taxa. Using x-ray microtomography, we show that Helicoforamina developed through one-, four-, and eight-cell stages, to hundreds and thousands of cells. Putative hatchlings are artifacts of incompletely preserved cyst walls. Our results preclude inclusion of Helicoforamina into life cycles assembled from other components of the Weng'an biota but support a holozoan affinity. The similarly ornamented encysted forms shared among the diverse Weng'an biota represent parallel adaptations to the temporally and spatially heterogeneous Ediacaran shallow marine environments.

Nucleus preservation in early Ediacaran Weng'an embryo-like fossils, experimental taphonomy of nuclei and implications for reading the eukaryote fossil record.

The challenge of identifying fossilized organelles has long hampered attempts to interpret the fossil record of early eukaryote evolution. We explore this challenge through experimental taphonomy of nuclei in a living eukaryote and microscale physical and chemical characterization of putative nuclei in embryo-like fossils from the early Ediacaran Weng'an Biota. The fossil nuclei exhibit diverse preservational modes that differ in shape, presence or absence of an inner body and the chemistry of the associated mineralization. The nuclei are not directly fossilized; rather, they manifest as external moulds. Experimental taphonomy of epidermal cells from the common onion (Allium cepa) demonstrates that nuclei are more decay resistant than their host cells, generally maintaining their physical dimensions for weeks to months post-mortem, though under some experimental conditions they exhibit shrinkage and/or become shrouded in microbial biofilms. The fossil and experimental evidence may be rationalized in a single taphonomic pathway of selective mineralization of the cell cytoplasm, preserving an external mould of the nucleus that is itself resistant to both decay and mineral replication. Combined, our results provide both a secure identification of the Weng'an nuclei as well as the potential of a fossil record of organelles that might help arbitrate in long-standing debates over the relative and absolute timing of the evolutionary assembly of eukaryote-grade cells.

The Early Ediacaran Caveasphaera Foreshadows the Evolutionary Origin of Animal-like Embryology.

The Ediacaran Weng'an Biota (Doushantuo Formation, 609 Ma old) is a rich microfossil assemblage that preserves biological structure to a subcellular level of fidelity and encompasses a range of developmental stages [1]. However, the animal embryo interpretation of the main components of the biota has been the subject of controversy [2, 3]. Here, we describe the development of Caveasphaera, which varies in morphology from lensoid to a hollow spheroidal cage [4] to a solid spheroid [5] but has largely evaded description and interpretation. Caveasphaera is demonstrably cellular and develops within an envelope by cell division and migration, first defining the spheroidal perimeter via anastomosing cell masses that thicken and ingress as strands of cells that detach and subsequently aggregate in a polar region. Concomitantly, the overall diameter increases as does the volume of the cell mass, but after an initial phase of reductive palinotomy, the volume of individual cells remains the same through development. The process of cell ingression, detachment, and polar aggregation is analogous to gastrulation; together with evidence of functional cell adhesion and development within an envelope, this is suggestive of a holozoan affinity. Parental investment in the embryonic development of Caveasphaera and co-occurring Tianzhushania and Spiralicellula, as well as delayed onset of later development, may reflect an adaptation to the heterogeneous nature of the early Ediacaran nearshore marine environments in which early animals evolved.