Chengjiang Biota Research Articles

Fossilization modes in the Chengjiang Lagerstätte (Cambrian of China): testing the roles of organic preservation and diagenetic alteration in exceptional preservation

One important, and poorly understood, issue concerning the taphonomy of nonmineralizing organisms in Cambrian Burgess Shale-type deposits is the diagenetic pathways by which organisms have become exceptionally preserved. Scanning electron microscopy (SEM) analyses of exceptionally preserved fossils from the lower Cambrian Chengjiang deposit of China demonstrate that nonmineralized tissue is preserved in a variety of ways, and further suggest that there was some taxonomic control over the precipitation of authigenic minerals during early diagenesis. Organic preservation is limited to certain decay-resistant structures such as heavily sclerotized spines on the claws of anomalocaridids. Labile organic tissues of nearly all nonmineralizing animals, however, are preserved by thin films of diagenetic minerals. Microstructural studies, energy-dispersive X-ray (EDX) analyses, and elemental mapping of these minerals indicate that mineral films include apatite, pyrite, and Fe-rich aluminosilicates. The results support the assumption that early diagenetic mineralization such as phosphatization and pyritization played a key role in the preservation of nonmineralized organisms. Pyritization seems to be the most important process by which nonmineralizing Chengjiang organisms are preserved in exceptional condition. Precipitation of Fe-rich aluminosilicates, which occurred following pyritization, also played a role in the preservation of some Chengjiang fossils. Phosphatization in the Chengjiang Lagerstätte was evidently rare, and limited taxonomically or to animals having large masses of organic material.

The lobopodianPaucipodia inermisfrom the Lower Cambrian Chengjiang fauna, Yunnan, China

New specimens of Paucipodia inermis Chen, Zhou & Ramskold, 1995, are described from the Lower Cambrian Chengjiang Lagerstatte in Haikou, Kunming. Details not previously seen in the Chengjiang material appear to be caused by early diagenetic processes. Some features not previously observed in Palaeozoic lobopodians include details of the dermomuscular sac, body cavities, contents of the gut, possible paired ventral nerve ganglia, and a rasping or biting apparatus with teeth. The latter implies a fundamental difference from onychophorans and rules out an ancestral position for Palaeozoic lobopodians. The supposed tail is shown to be the head, and it is shown that this animal possessed nine pairs of lobopods rather than six, as originally stated. The family Paucipodiidae n. fam. is introduced.

Evidence for a single median fin-fold and tail in the Lower Cambrian vertebrate, Haikouichthys ercaicunensis.

In this study, we illustrate an exceptionally well-preserved Haikouichthys ercaicunensis from the Lower Cambrian Chengjiang fauna that displays complete single dorsal, ventral and caudal fins. This 530-million-year old vertebrate is fish-shaped and characterized by a single median fin-fold, which is an essential trait of the initial vertebrate chordates. The radially orientated ray-like structures in its dorsal fin somewhat resemble but are probably not real radials seen in basal vertebrates, such as hagfishes and lampreys. The unique design of primitive fins and fin structures provides additional insights into the early evolution of vertebrates.

The earliest-known ancestors of Recent Priapulomorpha from the Early Cambrian Chengjiang Lagerstätte

The taxonomy of an early ancestor of Recent Priapulidae,Xiaoheiqingella peculiaris (=Yunnanpriapulus halteroformis Huang et al., 2004) from the Early Cambrian Chengjiang fossil Lagerstatte, is revised. Morphological characters comprise a pair of caudal appendages rather than a single appendage flanking the trunk end and a possible urogenital duct found inside the preanal region. An additional extremely rare fossil priapulid worm,Paratubiluchus bicaudatus gen. nov., sp. nov. is also described herein. Its diagnostic characters are: an introvert bearing 25 longitudinal rows of scalids, a distinct neck region, no annulus on the oval trunk, and a pair of caudal appendages. The proportion of body parts is similar in size to that of loricate larvae of Recent priapulids and larva-formed Palaeopriapulitidae. Taking account of the features ofXiaoheiqingella, bicaudal appendages are considered to be a synapomorphy of Priapulidae and Tubiluchidae.Paratubiluchus gen. nov. is most likely a candidate for the ancestor of the Tubiluchidae; it probably originated from a larva-formed priapulid with 25 rows of scalids, thus representing an intermediate link between the priapulids in mature-form and the priapulids with lorica.

Recent Priapulidae and their Early Cambrian ancestors: comparisons and evolutionary significance

Although priapulid worms form a relatively small phylum in present-day marine environments, they were important animals in Cambrian endobenthic communities. Two Early Cambrian priapulids, namely Xiaoheiqingella peculiaris and Yunnanpriapulus halteroformis nov. gen., nov. sp. from the Maotianshan Shale Lagerstätte of SW China are revised and described. Several key-features of the body plan of Recent Priapulidae are recognized in these two forms: 1) the four-fold body division (introvert, neck, trunk, and caudal appendage); 2) the well-developed introvert armed with ca. 25 longitudinal rows of scalids; 3) the caudal appendage; 4) the pharyngeal teeth arranged in a pentagonal disposition ( Xiaoheiqingella); 5) the ventral nerve cord present in Yunnanpriapulus. This morphology indicates close evolutionary relationships with modern priapulids. Xiaoheiqingella and Yunnanpriapulus nov. gen. are tentatively placed within the recent family Priapulidae. The Priapulidae lineage may therefore have a remote origin (Early Cambrian) much older than was previously assumed ( Priapulites; Late Carboniferous). The functional morphology of Xiaoheiqingella and Yunnanpriapulus nov. gen. suggests that these two worms were chiefly carnivorous with possible occasional mud-eating habits.

A new ‘great‐appendage’ arthropod from the Lower Cambrian of China and homology of chelicerate chelicerae and raptorial antero‐ventral appendages

The uniramous ‘great appendages’ of several arthropods from the Early to Middle Cambrian are a characteristic pair of pre-oral limbs, which served for prey capture. It has been assumed that the morphological differences between the ‘great-appendage’ arthropods indicate that raptorial antero-ventral and anteriorly pointing appendages evolved more than once in arthropod phylogeny. One set of Cambrian ‘great-appendage’ arthropods has, however, very similar short antero-ventral appendages with a peduncle of two segments angled against each other (elbowed) and with stout distally or medio-distally directed spines or long flexible flagellate spines on each of the four distal segments. Moreover, the head appendages of all these forms comprise the ‘great appendages’ and three pairs of biramous limbs. To this set of taxa we can add a new form from the Lower Cambrian Maotianshan Shale of southern China, Haikoucaris ercaiensis n. gen. and n. sp. It is known from three specimens, possibly being little abundant in the faunal community. It can be distinguished from all other taxa by the prominence of the proximal claw segment of its ‘great appendages’ and by only three distal spines (one on each of the distal segments). The similarity of the short, spiky ‘great appendages’ of Haikoucaris with the chelicera of the Chelicerata leads us to hypothesize that this particular type of ‘great appendages’ was the actual precursor of the chelicera. Homeobox gene and developmental data recently demonstrated the homology between the antenna of ateloceratans and the antennula of crustaceans on one side and the chelicera of chelicerates on the other. To this we add palaeontological evidence for the homology between the chelicerae of chelicerates and the ‘short great appendages’ of certain Cambrian arthropods, which leads us to hypothesize that the evolutionary path went from the ‘short great appendages’, by progressive compaction, toward the chelicera with only a two-spined chela. The new form from China is regarded as the possible latest offshoot, whereas the other ‘great appendages’ arthropods with similar short grasping limbs were derivatives of the stem lineage of the crown-group Chelicerata. Consequently, the chelicera with a chela with one fixed and one mobile finger is an autapomorphy of the crown group of Chelicerata, whereas a raptorial, but more limb-like antenna, with more distal spine-bearing segments, characterized the ground pattern of Chelicerata. Further taxa having ‘great appendages’, including the large Anomalocarididae, are also discussed in the light of their possible affinities to the Chelicerata and possible monophyly of all of these arthropods with raptorial anterior appendages.

Anatomy and lifestyles of Early Cambrian priapulid worms exemplified by Corynetis and Anningvermis from the Maotianshan Shale (SW China)

Accurate information on the anatomy and ecology of worms from the Cambrian Lagerstatten of SW China is sparse. The present study of two priapulid worms Anningvermis n. gen. and Corynetis Lou & Hu, 1999 from the Lower Cambrian Maotianshan Shale biota brings new information concerning the anatomical complexity, functional morphology and lifestyles of the Early Cambrian priapulids. Comparisons are made with Recent priapulids from Sweden (live observations, SEM). The cuspidate pharyngeal teeth of Anningvermis (circumoral pentagons) and the most peculiar radiating oral crown of Corynetis added to the very elongate pharynx of these two forms are interpreted as two different types of grasping apparatus possibly involved in the capture of small prey. Corynetis and Anningvermis are two representative examples of the Early Cambrian endobenthic communities largely dominated by priapulid worms (more than ten species in the Maotianshan Shale biota) and to a much lesser extent by brachiopods. Corynetis and Anningvermis were probably active mud-burrowers and predators of small meiobenthic animals. Likewise predator priapulid worms exploited the interface layer between the seawater and bottom sediment, where meiobenthic organisms were abundant and functioned as prey. This implies that complex prey-predator relationship between communities already existed in the Early Cambrian. This study also shows that the circumoral pentagonal teeth and caudal appendage were present in the early stages of the evolutionary history of the group and were important features of the priapulid body plan already in the Early Cambrian. Two new families, one new genus and new species are introduced and described in the appendix.

New data on the lophophore anatomy of Early Cambrian linguloids from the Chengjiang Lagerstätte, Southwest from the Chengjiang Lagerstätte, Southwest

Une succession de types de lophophore est decrite chez des brachiopodes linguloides dans les depots du Chengjiang (Cambrien inferieur) au Sud de la Chine. Ces types vont depuis un lophophore trocholophe, au schizolophe et au spirolophe a enroulement spiral simple. Cette succession d'âge Atdabanien existe encore dans le developpement du lophophore chez les linguloides actuels, ce qui demontre une similarite entre les lophophores au Cambrien et dans l'Actuel. Des dispositions aberrantes des bras lophophoraux qui tendent a s'etendre de facon inhabituelle dans et hors de la coquille sont illustrees dans une dizaine d'exemplaires.

Preservation of Early Cambrian animals of the Chengjiang biota

The Chengjiang biota of Yunnan, China, documents the earliest extensive radiation of the Metazoa recorded in the fossil record. Gauging preservational bias is crucial in providing an assessment of the completeness of this biota and thereby elucidating whether it represents a comprehensive depiction of Early Cambrian life. We here present a model to explain the nature of the exceptional preservation of the Chengjiang biota and details of the decay process. This study indicates that Chengjiang fossils were preserved through two taphonomic pathways that may have captured tissues of distinct compositions, and this finding should provide a foundation for the interpretation of Chengjiang fossils. Many Chengjiang fossils are preserved by pyrite (later pseudomorphed by iron oxides); the clay-rich host sediment was deficient in organic carbon but replete in available Fe, and this composition ensured that a decaying carcass acted as a local substrate for Fe- and S-reducing bacteria. Pyrite morphology probably reflects contrasts in the decay rate, and hence the H 2 S production rate, of different tissues in a carcass. Reactive, rapidly decaying tissues would have quickly supplied H 2 S, producing many pyrite nuclei, resulting in framboidal habits. More recalcitrant tissues would have produced H 2 S more slowly, so that crystal growth operated on fewer nuclei, resulting in larger euhedral pyrite crystals. Reflective films, especially common on Chengjiang arthropods, represent the remains of degraded carbon.

Possible developmental mechanisms underlying the origin of the crown lineages of arthropods

The extraordinarily preserved, diverse arthropod fauna from the Lower Cambrian Maotianshan shale, central Yunnan (southwest China), represents different evolutionary stages stepping from stem lineages towards crown arthropods (also called euarthropods), which makes this fauna extremely significant for discussion of the origin and early diversification of the arthropods. Anatomical analyses of the Maotianshan shale arthropods strongly indicate that the origin of crown arthropods involved three major evolutionary events, arthrodisation, arthropodisation and cephalization. We try to explore possible evolutionary changes of the developmental mechanism that may have underlain origins of euarthropod appendage and head. Fossil evidence suggests that the formation of a jointed limb known as arthropodisation and formation of multi-segmented head (called cephalization), which characterize euarthropods, is an event after arthrodisation characterized with the formation of segmented-exoskeleton and the joint membrane between tergites. We propose that the Hox complex was already operating at least as early as in the Early Cambrian and is responsible for the formation of the joint membrane between two semgents through Hox gene regulation along the D-V and P-D axis. Fossil evidence indicates that the head in ground state of arthropods consists only of two segments, an ocular and an antennal one. The formation of multiple segmented, euarthropod head (called syncephalon) from the two-segmented head was a separate event, which is called cephalization. Presence of the Hox gene head expression domain and change of developmental mechanism in head segments might be responsible for the formation of the syncephalon and this event has been broadly finished in the Early Cambrian arthropods. The post-oral limbs in the early syncephalons as evidenced from the Lower Cambrian Maotianshan shale arthropods however were almost identical to those in trunk. Therefore we proposed that the Hox genes specifiedexpression in individual segment was a late evolutionary step postdating the formation of syncephalon.

Early Cambrian lingulate brachiopods from the Shaanxi Province, China

A diverse fauna of lingulate (Subphylum Linguliformea, Class Lingulata) brachiopods is described from the Early Cambrian (Qiongzhusian Stage) carbonates in southern Shaanxi Province (Fucheng and Xiaoyang sections), China. Eight species assigned to 6 genera are systematically described. Among them, the taxa assigned to the Superfamily Linguloidea comprise Palaeobolus liantuoensis Zeng, Lingulellotreta malongensis (Rong), Eoobolus aff. viridis (Cobbold), Eoobolus? shaanxiensis sp. nov., and Kyrshabaktella? sp. Only Palaeobolus liantuoensis and Lingulellotreta malongensis were known previously from South China, where the latter species occurs in the soft-bodied Chengjiang fauna with preserved pedicle. The Superfamily Acrotheloidea is represented only by the new species Botsfordia minuta. The fauna also includes two primitive acrotretoid (Superfamily Acrotretoidea) species belonging to the new genus and species Eohadrotreta zhenbaensis and E. zhujiahensis; the ontogeny of Eohadrotreta supports the view that the acrotretid muscle system and ontogeny are derived in relation to the lingulide musculature and ontogeny. The fauna from Shaanxi is the oldest known diverse lingulate brachiopod assemblage from China.

The occurrence of the genus Marrella (Trilobitoidea) in Asia *

Abstract An important discovery in the Kaili Biota has been made recently, and many interesting components from Chengjiang Biota and Burgess Shale Biota have been discovered. Among them Marrella, only known from mid-Middle Cambrian Burgess Shale Biota of British Columbia, Canada, is one of the most important arthropods fossils. Because the Kaili Biota is older than the Burgess Shale Biota, the strange head shield of Marrella occurring in the Kaili Biota outside Laurentia ranges from mid-Middle Cambrian to early Middle Cambrian and is significant for the reconstruction of palaeogeography and evolutionary study of early metazoa. In the present paper Marrella sp. is reported for the first time in Asia.

A New Vetulicolian from the Early Cambrian Chengjiang Fauna in Yunnan of China

Abstract The genus and species Yuyuanozoon magnificissimi gen. et sp. nov., a new fossil vetulicolian, is reported from the Early Cambrian Chengjiang Fauna in Yunnan of China. It has a bipartite body plan and five pairs of chain‐formed gill sacs, showing the general characteristics of Ventulicolia. However, the exclusive “atrial cavity” and external gill observed indicate that the new form is different from those previously described as vetulicolians, probably representing a lineage developed within deuterostomes and more primitive than urochordates.

Evidence of lophophore diversity in Early Cambrian Brachiopoda

The lophophore, an essential organ of the Brachiopoda, has been used widely in evolutionary and advanced phylogenetic studies, but is hitherto unknown in the fossil record. Here, the extraordinarily well-preserved lophophores of two inarticulated brachiopods Lingulella chengjiangensis and Heliomedusa orienta, from the Lower Cambrian Chengjiang fauna (Yunnan, China) are described. These primitive lophophores, respectively, trocholophous and schizolophous, have some key characters that may be plesiomorphies inherited by their recent descendants. This discovery provides direct evidence regarding the taxonomy, ecosystems and early evolution of inarticulated brachiopods.

Response to Comment on "A New Species of Yunnanozoan with Implications for Deuterostome Evolution"

The combination of complex taphonomies and bizarre anatomies in Chengjiang fossils can lead to radical divergences of opinion concerning phylogenetic placements. Yunnanozoans exemplify this difficulty, but the proposal by Mallatt et al . ( [1][1] ) that they represent some sort of protovertebrate is

The Chengjiang fauna — the oldest preserved animal community

The Chengjiang fauna, an exceptionally well-preserved fossil lagerstatte, from the lower part of the Lower Cambrian Eoredlichia-Wutingaspis Biozone in the Kunming area, Yunnan Province, China is generally introduced, including the research history of the area, stratigraphy in the interval with soft-bodied fossils, geological setting, depositional environment, discovery, distribution, significance and faunal association. The Chengjiang lagerstatte yields various mineralized and nonmineralized skeletons and internal soft parts of organisms, as well as complete soft-bodied animals. The fauna includes virtually all animal phyla that were previously known from the Middle Cambrian and vividly reproduces the appearance of the oldest Phanerozoic animals.

A New Platy‐armored Worm from the Early Cambrian Chengjiang Lagerstätte, South China

Abstract The Lower Cambrian Chengjiang Lagerstätte provides a good window to explore the origin and radiation of early bilaterians. Here we describe a netted sclerite‐bearing worm Tabelliscolex hexagonus gen. et sp. nov., and tentatively assign it to palaeoscolecidans of priapulids. The cuticle of the animal is covered with two kinds of platy sclerites which are constructed by hexagonally arranged tubercles. Similar structures of the sclerites can be seen on some Cambrian palaeoscolecidans and lobopods, so, this new species is critical for understanding the relationships between lobopods and palaeoscolecidans.

Exceptional Fossil Preservation and the Cambrian Explosion

Exceptionally preserved, non-biomineralizing fossils contribute importantly to resolving details of the Cambrian explosion, but little to its overall patterns. Six distinct "types" of exceptional preservation are identified for the terminal Proterozoic-Cambrian interval, each of which is dependent on particular taphonomic circumstances, typically restricted both in space and time. Taphonomic pathways yielding exceptional preservation were particularly variable through the Proterozoic-Cambrian transition, at least in part a consequence of contemporaneous evolutionary innovations. Combined with the reasonably continuous record of "Doushantuo-type preservation," and the fundamentally more robust records of shelly fossils, phytoplankton cysts and trace fossils, these taphonomic perturbations contribute to the documentation of major evolutionary and biogeochemical shifts through the terminal Proterozoic and early Cambrian.Appreciation of the relationship between taphonomic pathway and fossil expression serves as a useful tool for interpreting exceptionally preserved, often problematic, early Cambrian fossils. In shale facies, for example, flattened non-biomineralizing structures typically represent the remains of degradation-resistant acellular and extracellular "tissues" such as chaetae and cuticles, whereas three-dimensional preservation represents labile cellular tissues with a propensity for attracting and precipitating early diagenetic minerals. Such distinction helps to identify the acuticular integument of hyolithids, the chaetae-like nature of Wiwaxia sclerites, the chaetognath-like integument of Amiskwia, the midgut glands of various Burgess Shale arthropods, and the misidentification of deposit-feeding arthropods in the Chengjiang biota. By the same reasoning, putative lobopods in the Sirius Passet biota and putative deuterostomes in the Chengiang biota are better interpreted as arthropods.

A possible Lower Cambrian chaetognath (arrow worm).

A possible Lower Cambrian chaetognath (arrow worm).

Possible ctenophoran affinities of the Precambrian "sea-pen" Rangea.

The Namibian Kuibis Quartzite fossils of Rangea are preserved three-dimensionally owing to incomplete collapse of the soft tissues under the load of instantaneously deposited sand. The process of fossilization did not reproduce the original external morphology of the organism but rather the inner surface of collapsed organs, presumably a system of sacs connected by a medial canal. The body of Rangea had tetraradial symmetry, a body plan shared also by the White Sea Russian fossil Bomakellia and possibly some other Precambrian frond-like fossils. They all had a complex internal anatomy, smooth surface of the body, and radial membranes, making their alleged colonial nature unlikely. Despite a different style of preservation, the Middle Cambrian Burgess Shale frond-like Thaumaptilon shows several anatomical similarities to Rangea. The body plan of the Burgess Shale ctenophore Fasciculus, with its numerous, pinnately arranged comb organs, is in many respects transitional between Thaumaptilon and the Early Cambrian ctenophore Maotianoascus from the Chengjiang fauna of South China. It is proposed that the irregularly distributed dark spots on the fusiform units of the petaloid of Thaumaptilon represent a kind of macrocilia and that the units are homologous with the ctenophoran comb organs. These superficial structures were underlain by the complex serial organs, well represented in the fossils of Rangea. The Precambrian "sea-pens" were thus probably sedentary ancestors of the ctenophores.