Zongjun Yin

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

Significance Phylogenomic extrapolations indicate the last common ancestor of sponges and eumetazoans existed deep in the Cryogenian, perhaps 200 million years (Myr) before the Cambrian (541 Ma). This inference implies a long Precambrian history of animals phylogenetically allied with sponges. However, there is yet little unequivocal paleontological evidence of Precambrian sponges. Here, we present a newly discovered 600-Myr-old fossil preserved at cellular resolution, displaying multiple poriferan features. The animal was covered with a dense layer of flattened cells resembling sponge pinacocytes, displaying a hollow tubular structure with apparent water inflow and outflow orifices. Although requiring additional specimens of similar form for confirmation, this finding is consistent with phylogenomic inference, and implies the presence of eumetazoan ancestors by 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.

Diversity and species abundance patterns of the Early Cambrian (Series 2, Stage 3) Chengjiang Biota from China

Abstract Lagerstätten from the Precambrian–Cambrian transition have traditionally been a relatively untapped resource for understanding the paleoecology of the “Cambrian explosion.” This quantitative paleoecological study is based on 10,238 fossil specimens belonging to 100 animal species, 11 phyla, and 15 ecological categories from the lower Cambrian (Series 2, Stage 3) Chengjiang biota (Mafang locality near Haikou, Yunnan Province, China). Fossils were systematically collected within a 2.5-meter-thick sequence divided into ten stratigraphic intervals. Each interval represents an induced time-averaged assemblage of various event (obrution) beds of unknown duration. Overall, the different fossil assemblages are taxonomically and ecologically similar, suggesting the presence of a single community type recurring throughout the Mafang section. The Mafang community is dominated by epibenthic vagile hunters or scavengers, sessile suspension feeders, and infaunal vagile hunters or scavengers represented primarily by arthropods, brachiopods, and priapulids, respectively. Most species have low abundance and low occurrence frequencies, whereas a few species are numerically abundant and occur frequently. Overall, in structure and ecology the Mafang community is comparable to the Middle Cambrian (Series 3, Stage 5) Burgess Shale biota (Walcott Quarry, Yoho National Park, British Columbia, Canada). This suggests that, despite variations in species identity within taxonomic and ecological groups, the structure and ecology of Cambrian Burgess Shale-type communities remained relatively stable until at least the Middle Cambrian (Series 3, Stage 5) in subtidal to relatively deep-water offshore settings in siliciclastic soft-substrate environments.

Decimetre-scale multicellular eukaryotes from the 1.56-billion-year-old Gaoyuzhuang Formation in North China

Fossils of macroscopic eukaryotes are rarely older than the Ediacaran Period (635–541 million years (Myr)), and their interpretation remains controversial. Here, we report the discovery of macroscopic fossils from the 1,560-Myr-old Gaoyuzhuang Formation, Yanshan area, North China, that exhibit both large size and regular morphology. Preserved as carbonaceous compressions, the Gaoyuzhuang fossils have statistically regular linear to lanceolate shapes up to 30 cm long and nearly 8 cm wide, suggesting that the Gaoyuzhuang fossils record benthic multicellular eukaryotes of unprecedentedly large size. Syngenetic fragments showing closely packed ∼10 μm cells arranged in a thick sheet further reinforce the interpretation. Comparisons with living thalloid organisms suggest that these organisms were photosynthetic, although their phylogenetic placement within the Eukarya remains uncertain. The new fossils provide the strongest evidence yet that multicellular eukaryotes with decimetric dimensions and a regular developmental program populated the marine biosphere at least a billion years before the Cambrian Explosion.

Meroblastic cleavage identifies some Ediacaran Doushantuo (China) embryo-like fossils as metazoans

Ediacaran Doushantuo (Formation) embryo-like fossils (EDEFs, ca. 600 Ma) from South China display cellular and sub-cellular structures and provide a unique window on the early evolution of multicellular eukaryotes. But there have been widely disparate interpretations of these fossils. Here we report new fossil embryo-like forms from the Doushantuo phosphorite that exhibit a meroblastic cleavage pattern. Our results from high-resolution propagation phase contrast–synchrotron radiation X-ray microtomography (PPC-SRµCT) demonstrate that these fossils preserve features directly comparable to those of modern meroblastic animal embryos that utilize discoidal cleavage. Given that discoidal-type meroblastic cleavage occurs only in metazoans, the phylogenetic positions of these fossils probably fall into the animal branch of the holozoan tree. Meroblastic as well as holoblastic cleavage forms were thus present by ca. 600 Ma, substantiating the conclusion derived from molecular clock estimates that a variety of metazoan lineages had evolved by the mid-Ediacaran after the termination of the Marinoan glaciation, if not earlier.

Appendages of an early Cambrian metadoxidid trilobite from Yunnan, SW China support mandibulate affinities of trilobites and artiopods

Appendage anatomy contributes crucial data for understanding the evolution and ecology of Euarthropoda. The Palaeozoic trilobites show a great diversity of exoskeletons in the fossil record. However, soft parts, especially appendages, have only been discovered from a few trilobite species. Here we report extraordinarily preserved appendages in the trilobite species Hongshiyanaspis yiliangensis Zhang & Lin in Zhang et al . 1980 (Redlichiida, Metadoxididae) from a single mudstone layer of the Xiazhuang fossil assemblage within the Hongjingshao Formation (Cambrian Series 2, Stage 3) near Kunming, Yunnan, SW China. The appendages exhibit the common architecture revealed by other trilobites and artiopods by consisting of a pair of uniramous antennae followed by a series of paired homonomous biramous limbs. The antennae in holaspid individuals comprise up to 27 spinous podomeres and their ontogeny occurs by lengthening of the podomeres. The post-antennal biramous limbs are similar to those in other polymerid trilobites and artiopods by having a single-segmented protopodite and an endopodite comprising seven segments, but possess a unique wide tripartite exopodite with long setae. Sophisticated appendage anatomy, including the body–limb junction, fine setae, putative muscle bundles and duct-type tissues, are also revealed. Appendages of trilobites, artiopods and other upper stem-group euarthropods are compared and summarized. The H. yiliangensis appendages highlight the high morphological disparity of exopodites and the conservativeness of endopodites in trilobites and artiopods. This morphological pattern, together with similar body patterning seen in crustaceans but not in chelicerates, supports the mandibulate affinities of trilobites and at least some artiopods.

First report of Wiwaxia from the Cambrian Chengjiang Lagerstätte

Research was supported by the Chinese Academy of Sciences (KZZD-EW-02-2); the National Basic Research Program of China (2013CB835006); the National Natural Science Foundation of China (41472012); the Natural Science Foundation of Jiangsu Province (BK2012893); and Clare College, Cambridge.

Morphology of diverse radiodontan head sclerites from the early Cambrian Chengjiang Lagerstätte, south-west China

Recorded in exceptionally preserved Lagerstätten, the radiodontans (including anomalocaridids) are cosmopolitan, soft-bodied, stem-group euarthropods that inhabited Palaeozoic seas. They are notable for their unique morphology, peculiar ecology and basal position in euarthropod evolution. The early Cambrian Chengjiang Lagerstätte has yielded some of the oldest radiodontans, including three unquestionable taxa – Anomalocaris saron Hou et al., 1995, Amplectobelua symbrachiata Hou et al., 1995 and Lyrarapax unguispinus Cong et al., 2014 – based on articulated specimens. However, recent discoveries of the Burgess Shale Hurdia Walcott, 1912 and the Fezouata Aegirocassis benmoulae Van Roy et al., 2015 highlight the presence of another radiodontan group (Hurdiidae) characterized by a tripartite head sclerite complex consisting of one central element and a pair of lateral elements. Here, we describe six morphotypes of possible hurdiid head sclerite elements from the Chengjiang Lagerstätte, some of which are closely associated with other typical radiodontan body parts. These, recognized as central elements, include two new species of the same new genus, Tauricornicaris latizonae gen. et sp. nov. and T. oxygonae gen. et sp. nov., and a former bivalved euarthropod, Zhenghecaris shankouensis Vannier et al., 2006. Another three unnamed sclerite elements are identified as lateral elements. These sclerite elements from Chengjiang provide detailed anatomy, such as mammillary tubercles and soft-tissue reticulate structure, to help understand the morphology and biology of all hurdiid head sclerites. A common single dorsal plate in Anomalocaris saron and Amplectobelua symbrachiata is confirmed. Although the morphologically diverse central and lateral elements of the Hurdiidae and the conserved dorsal plate of the Anomalocarididae + Amplectobeluidae reflect a major distinction in radiodontan body plans, they share a fundamental structure of double layers of cuticle. The Chengjiang specimens not only clarify the morphology and biology of the radiodontan head sclerites in general, but also illuminate the diversity and disparity of radiodontans in their early evolutionary history. http://zoobank.org/urn:lsid:zoobank.org:pub:D0590390-A85A-493A-8529-B2DF64D91169

A new radiodontan oral cone with a unique combination of anatomical features from the early Cambrian Guanshan Lagerstätte, eastern Yunnan, South China

Abstract. The radiodontans, including anomalocaridids and their allies, are enigmatic stem-group euarthropods and are the most ancient apex giant predators known from the fossil record. Most studies on their feeding behaviors have emphasized their diverse and abundant raptorial frontal appendages, while the oral cone surrounding the mouth opening in these animals has attracted less attention. At present, three oral cone morphotypes are known, from Anomalocaris Whiteaves, 1892, Peytoia Walcott, 1911, and Hurdia Walcott, 1912, respectively. In this paper, we report on a novel form of radiodontan oral cone from the Guanshan Lagerstätte (Cambrian Series 2, Stage 4) in the Wulongqing Formation, eastern Yunnan, South China. This oral cone is unique in combining features seen in Peytoia/Hurdia and Anomalocaris. It possesses a Peytoia/Hurdia-type ‘tetraradial’ configuration comprising a 32-plate outer ring that consists of four perpendicularly arranged large plates and 28 small plates, in addition to furrowed folds and scale-like nodes on plate surfaces otherwise seen only in Anomalocaris. As an intermediate morphotype, the Guanshan oral cone improves our understanding of the occurrence and morphological disparity of radiodontan oral cones, illuminates future investigations on potentially variable radiodontan feeding mechanisms, and reveals possible evolutionary transformations of these peculiar feeding structures. The resolution of current radiodontan phylogeny would be potentially improved by new knowledge on other body parts apart from frontal appendages in future studies.

Orthrozanclus elongata n. sp. and the significance of sclerite-covered taxa for early trochozoan evolution

Orthrozanclus is a shell-bearing, sclerite covered Cambrian organism of uncertain taxonomic affinity, seemingly representing an intermediate between its fellow problematica Wiwaxia and Halkieria. Attempts to group these slug-like taxa into a single ‘halwaxiid’ clade nevertheless present structural and evolutionary difficulties. Here we report a new species of Orthrozanclus from the early Cambrian Chengjiang Lagerstätte. The scleritome arrangement and constitution in this material corroborates the link between Orthrozanclus and Halkieria, but not with Wiwaxia — and calls into question its purported relationship with molluscs. Instead, the tripartite construction of the halkieriid scleritome finds a more compelling parallel in the camenellan tommotiids, relatives of the brachiopods and phoronids. Such a phylogenetic position would indicate the presence of a scleritome in the common ancestor of the three major trochozoan lineages, Mollusca, Annelida and Brachiozoa. On this view, the absence of fossil Ediacaran sclerites is evidence against any ‘Precambrian prelude’ to the explosive diversification of these phyla in the Cambrian, c. 540–530 million years ago.