Xingliang Zhang

Head and backbone of the early Cambrian vertebrate Haikouichthys

Agnathan fish hold a key position in vertebrate evolution, especially regarding the origin of the head and neural-crest-derived tissue. In contrast to amphioxus, lampreys and other vertebrates possess a complex brain and placodes that contribute to well-developed eyes, as well as auditory and olfactory systems. These sensory sytems were arguably a trigger to subsequent vertebrate diversifications. However, although they are known from skeletal impressions in younger Palaeozoic agnathans, information about the earliest records of these systems has been largely wanting. Here we report numerous specimens of the Lower Cambrian vertebrate Haikouichthys ercaicunensis, until now only known from the holotype. Haikouichthys shows significant differences from other fossil agnathans: key features include a small lobate extension to the head, with eyes and possible nasal sacs, as well as what may be otic capsules. A notochord with separate vertebral elements is also identifiable. Phylogenetic analysis indicates that this fish lies within the stem-group craniates. Although Haikouichthys somewhat resembles the ammocoete larva of modern lampreys, this is because of shared general craniate characters; adult lampreys and hagfishes (the cyclostomes if monophyletic) are probably derived in many respects.

Primitive deuterostomes from the Chengjiang Lagerstätte (Lower Cambrian, China)

Cambrian fossil-Lagerstätten (sites of exceptional fossil preservation), such as those from Chengjiang (Lower Cambrian) and the Burgess Shale (Middle Cambrian), provide our best window into the Cambrian ‘explosion’. Such faunas are known from about 40 localities, and have yielded a widely disparate series of taxa ranging from ctenophores to agnathan fish. Recent excavations of the Chengjiang fossil-Lagerstätte, known from a series of sites near Kunming in Yunnan, south China, have resulted in the discovery of several new forms. In conjunction with material described earlier, these provide evidence for a new group of metazoans, the vetulicolians. Several features, notably a series of gill slits, suggest that this group can throw light on an early stage of deuterostome diversification.

New sites of Chengjiang fossils: crucial windows on the Cambrian explosion

Soft-bodied and lightly sclerotized Chengjiang fossils have been found at more than ten new localities in the Lower Cambrian Qiongzhusi and Canglangpu formations of east central Yunnan. At the same time, three different fossil assemblages have been recognized, i.e. Kunmingella–Isoxys–Naraoia assemblage at Chengjiang, Kunmingella–Cricocosmia assemblage at Haikou, and Kunmingella–Wutingaspis–Obolus assemblage at Anning and Wuding. These sites yield new and striking specimens, such as a new tentacular animal, brachiopods with pedicles preserved, and the enigmatic Xidazoon (having mixed phyla characters), which are significant in our understanding of animal phylogeny. Above all, the appearance of diverse chordates and agnathans (vertebrates) greatly expands our knowledge of the Cambrian explosion. The discovery of soft-bodied fossils at many new localities and the very wide distribution of the Qiongzhusi Formation suggest that many more localities remain to be discovered. Here, a new early form of tentaculate, Cambrotentacus sanwuia gen. et sp. nov. (perhaps related to lophophorates and entoprocts), is described.

Reconsideration of the supposed naraoiid larva from the Early Cambrian Chengjiang Lagerstätte, South China

The Chengjiang Lagerstatte in the Lower Cambrian of South China yields a small, larva-like arthropod, which was considered to be a protaspis of naraoiids by many authors. The discovery of a large number of well-preserved specimens from many new localities has allowed the original study to be revised. The relatively large size, stable morphology and unusual structure of the appendages indicate that these specimens represent adults of a new arthropod, Primicaris larvaformis. The larva-like outline is considered to have arisen by the heterochronic process of progenesis. In addition, this animal displays primitive aspects of bodyplan and limb morphology that suggest a basal position within arachnomorphs, or perhaps even arthropods, and the similarities to the Vendian arthropod-like animal Parvancorina probably provide an evolutionary link between Vendian forms and Cambrian arthropods.

Anatomy and systematic affinities of the Lower Cambrian bivalved arthropod Isoxys auritus

Soft parts of Isoxys auritus, such as antennae, biramous limbs, eyes, mouth, stomach and adductor muscle scars, have been discovered in material from the Early Cambrian Chengjiang fossil Lagerstatte in Yunnan, South China. Isoxys auritus bears two pairs of antennae and eleven pairs of primitive biramous appendages which suggest it to be a stem-lineage crustacean.

A sclerite-bearing stem group entoproct from the early Cambrian and its implications

The Lophotrochozoa includes disparate tentacle-bearing sessile protostome animals, which apparently appeared in the Cambrian explosion, but lack an uncontested fossil record. Here we describe abundant well preserved material of Cotyledion tylodes Luo et Hu, 1999, from the Cambrian (Series 2) Chengjiang deposits, reinterpreted here as a stem-group entoproct. The entoproct affinity is supported by the sessile body plan and interior soft anatomy. The body consists of an upper calyx and a lower elongate stalk with a distal holdfast. The soft anatomy includes a U-shaped gut with a mouth and aboral anus ringed by retractable marginal tentacles. Cotyledion differs from extant entoprocts in being larger, and having the calyx and the stalk covered by numerous loosely-spaced external sclerites. The description of entoprocts from the Chengjiang biota traces the ancestry of yet another lophotrochozoan phylum back to the Cambrian radiation, and has important implications for the earliest evolution of lophotrochozoans.

An early Cambrian agglutinated tubular lophophorate with brachiopod characters

The morphological disparity of lophotrochozoan phyla makes it difficult to predict the morphology of the last common ancestor. Only fossils of stem groups can help discover the morphological transitions that occurred along the roots of these phyla. Here, we describe a tubular fossil Yuganotheca elegans gen. et sp. nov. from the Cambrian (Stage 3) Chengjiang Lagerstätte (Yunnan, China) that exhibits an unusual combination of phoronid, brachiopod and tommotiid (Cambrian problematica) characters, notably a pair of agglutinated valves, enclosing a horseshoe-shaped lophophore, supported by a lower bipartite tubular attachment structure with a long pedicle with coelomic space. The terminal bulb of the pedicle provided anchorage in soft sediment. The discovery has important implications for the early evolution of lophotrochozoans, suggesting rooting of brachiopods into the sessile lophotrochozoans and the origination of their bivalved bauplan preceding the biomineralization of shell valves in crown brachiopods.

A new arthropod from the Chengjiang Lagerstätte, Early Cambrian, southern China

A new genus and species of lightly sclerotized arthropod with an Aglaspis-like tagmosis, Kwanyinaspis maotianshanensis, is described from the well-known Chengjiang Lagerstätte, Early Cambrian, Yunnan, South China, on the basis of a single exquisitely preserved specimen. The dorsal exoskeleton, showing a poorly defined axial region but lacking axial furrows, is composed of a cephalic shield, 12 trunk tergites with well-developed pleural spines and a tail spine. A pair of ventral eyes is present beneath the first quarter of the cephalic shield. Appendages are preserved in remarkable detail; the basis is a large, flat plate, and bears gnathobases ventrally; the endopod is articulated with the abaxial edge of the basis and comprises seven articles; the exopod is flap-like and articulated along the entire length of the dorsal margin of the basis. Kwanyinaspis is provisionally assigned to Aglaspidida due to its overall resemblance to Aglaspis.

New occurrence of the Burgess Shale arthropod Sidneyia in the Early Cambrian Chengjiang Lagerstätte (South China), and revision of the arthropod Urokodia

A single specimen of Sidneyia Walcott, 1911, from the Early Cambrian Chengjiang Lagerstätte in the Maotianshan section, Yunnan Province, is the first occurrence of the genus outside Laurentia. The specimen shows the basic characteristics of Sidneyia: the body is composed of a cephalon with long (sag.) doublure, a thorax of nine articulating somites, an abdomen of two or three somites and a telson with lateral flaps. The cephalon, however, is semi-elliptical in dorsal view and the telson elongate, differing from the rectangular cephalon and the triangular telson of the type species Sidneyia inexpectans. Accordingly, a new species, Sidneyia sinica, is erected. In addition, a near-complete specimen of Urokodia aequalis from the Chengjiang fauna, in the Haoyicun section, Yunnan Province, provides new information on the trunk and tail shield morphology, necessitating a revision of its diagnosis.

A NEW ARTHROPOD PYGMACLYPEATUS DAZIENSIS FROM THE EARLY CAMBRIAN CHENGJIANG LAGERSTÄTTE, SOUTH CHINA

The early Cambrian Chengjiang Lagerstatte, generally regarded as late Atdabanian (Qian and Bengtson, 1989; Bengtson et al., 1990), has become celebrated for perhaps the earliest biota of soft-bodied organisms known from the fossil record and has proven to be critical to our understanding of early metazoan evolution. The Sirius Passet fauna from Peary Land, North Greenland, another important repository of soft-bodied and poorly sclerotized fossils, was also claimed as Early Cambrian (Conway Morris et al., 1987; Budd, 1995). The exact stratigraphic position of the Sirius Passet fauna (Buen Formation) is still uncertain, although the possibility of late Atdabanian age was proposed (Vidal and Peel, 1993). Recent work dates it in the “ Nevadella ” Biozone (Budd and Peel, 1998). It therefore appears to be simultaneous with or perhaps slightly younger than Chengjiang Lagerstatte, Eoredlichia Biozone (Zhuravlev, 1995). The Emu Bay Shale of Kangaroo Island, South Australia, has long been famous as a source of magnificent specimens of the trilobites Redlichia takooensis and Hsunaspis bilobata. It is additionally important as the only site in Australia so far to yield a Burgess-Shale-type biota (Glaessner, 1979; Nedin, 1992). The Emu Bay Shale was considered late Early Cambrian in age (Daily, 1956; Opik, 1975). But Zhang et al.(1980) reassessed its age based on data from the Chinese Early Cambrian. The occurrence of Redlichia takooensis and closely related species of Hsunaspis indicates an equivalence to the Tsanglangpuian in the Chinese sequence, and the contemporary South Australia fauna correlate with the Botomian of Siberia (Bengtson et al., 1990). Thus the Emu Bay Shale is younger than the upper Atdabanian Chengjiang Lagerstatte, Chiungchussuian. The initial material of Chengjiang Lagerstatte came primarily from the classic Maotianshan section and its vicinity (Zhang and Hou, 1985; Hou et al., 1991; Chen and Erdtmann, …