A venomous arthropod in the Early Cambrian Sea

A number of recently evolved animals possess poison glands for feeding and/or defense.However,examples of such animals are rare in the fossil record.We report a fossil arthropod Isoxys curvirostratus from the Early Cambrian Chengjiang biota of China.This species is regarded as the oldest known venomous arthropod based on the presence of venomous glands in its head region.The adult animal is 2-5 cm long and the body is covered entirely with a carapace.The presence of large stalk eyes and a pair of stout grasping appendages with a terminal spine suggest it was raptorial.Interestingly,the two pear-shaped,three-dimensionally preserved objects that are present in the head region and at the base of the grasping appendages closely resemble the venom glands of some living arthropods in size,shape,and position.These features indicate that the presence of venomous predators could date back 520 million years.Furthermore,our observations suggest that the feeding strategies and organs adapted for this purpose had already reached a high level of diversity and anatomical sophistication in the Early Cambrian ecosystems.     

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     

Homology of arthropod anterior appendages revealed by Hox gene expression in a sea spider

Arthropod head segments offer a paradigm for understanding the diversification of form during evolution, as a variety of morphologically diverse appendages have arisen from them. There has been long-running controversy, however, concerning which head appendages are homologous among arthropods, and from which ancestral arrangement they have been derived. This controversy has recently been rekindled by the proposition that the probable ancestral arrangement, with appendages on the first head segment, has not been lost in all extant arthropods as previously thought, but has been retained in the pycnogonids, or sea spiders. This proposal was based on the neuroanatomical analysis of larvae from the sea spider Anoplodactylus sp., and suggested that the most anterior pair of appendages, the chelifores, are innervated from the first part of the brain, the protocerebrum. Our examination of Hox gene expression in another sea spider, Endeis spinosa, refutes this hypothesis. The anterior boundaries of Hox gene expression domains place the chelifore appendages as clearly belonging to the second head segment, innervated from the second part of the brain, the deutocerebrum. The deutocerebrum must have been secondarily displaced towards the protocerebrum in pycnogonid ancestors. As anterior-most appendages are also deutocerebral in the other two arthropod groups, the Euchelicerata and the Mandibulata, we conclude that the protocerebral appendages have been lost in all extant arthropods.     

A giant Ordovician anomalocaridid

Anomalocaridids, giant lightly sclerotized invertebrate predators, occur in a number of exceptionally preserved early and middle Cambrian (542-501?million years ago) biotas and have come to symbolize the unfamiliar morphologies displayed by stem organisms in faunas of the Burgess Shale type. They are characterized by a pair of anterior, segmented appendages, a circlet of plates around the mouth, and an elongate segmented trunk lacking true tergites with a pair of flexible lateral lobes per segment. Disarticulated body parts, such as the anterior appendages and oral circlet, had been assigned to a range of taxonomic groups--but the discovery of complete specimens from the middle Cambrian Burgess Shale showed that these disparate elements all belong to a single kind of animal. Phylogenetic analyses support a position of anomalocaridids in the arthropod stem, as a sister group to the euarthropods. The anomalocaridids were the largest animals in Cambrian communities. The youngest unequivocal examples occur in the middle Cambrian Marjum Formation of Utah but an arthropod retaining some anomalocaridid characteristics is present in the Devonian of Germany. Here we report the post-Cambrian occurrence of anomalocaridids, from the Early Ordovician (488-472?million years ago) Fezouata Biota in southeastern Morocco, including specimens larger than any in Cambrian biotas. These giant animals were an important element of some marine communities for about 30?million years longer than previously realized. The Moroccan specimens confirm the presence of a dorsal array of flexible blades attached to a transverse rachis on the trunk segments; these blades probably functioned as gills.     

Neuroanatomy of sea spiders implies an appendicular origin of the protocerebral segment

Independent specialization of arthropod body segments has led to more than a century of debate on the homology of morphologically diverse segments, each defined by a lateral appendage and a ganglion of the central nervous system. The plesiomorphic composition of the arthropod head remains enigmatic because variation in segments and corresponding appendages is extreme. Within extant arthropod classes (Chelicerata, Myriapoda, Crustacea and Hexapoda--including the insects), correspondences between the appendage-bearing second (deutocerebral) and third (tritocerebral) cephalic neuromeres have been recently resolved on the basis of immunohistochemistry and Hox gene expression patterns. However, no appendage targets the first ganglion, the protocerebrum, and the corresponding segmental identity of this anterior region remains unclear. Reconstructions of stem-group arthropods indicate that the anteriormost region originally might have borne an ocular apparatus and a frontal appendage innervated by the protocerebrum. However, no study of the central nervous system in extant arthropods has been able to corroborate this idea directly, although recent analyses of cephalic gene expression patterns in insects suggest a segmental status for the protocerebral region. Here we investigate the developmental neuroanatomy of a putative basal arthropod, the pycnogonid sea spider, with immunohistochemical techniques. We show that the first pair of appendages, the chelifores, are innervated at an anterior position on the protocerebrum. This is the first true appendage shown to be innervated by the protocerebrum, and thus pycnogonid chelifores are not positionally homologous to appendages of extant arthropods but might, in fact, be homologous to the 'great appendages' of certain Cambrian stem-group arthropods.     

Acute vision in the giant Cambrian predator Anomalocaris and the origin of compound eyes

Until recently, intricate details of the optical design of non-biomineralized arthropod eyes remained elusive in Cambrian Burgess-Shale-type deposits, despite exceptional preservation of soft-part anatomy in such Konservat-Lagerst?tten. The structure and development of ommatidia in arthropod compound eyes support a single origin some time before the latest common ancestor of crown-group arthropods, but the appearance of compound eyes in the arthropod stem group has been poorly constrained in the absence of adequate fossils. Here we report 2-3-cm paired eyes from the early Cambrian (approximately 515 million years old) Emu Bay Shale of South Australia, assigned to the Cambrian apex predator Anomalocaris. Their preserved visual surfaces are composed of at least 16,000 hexagonally packed ommatidial lenses (in a single eye), rivalling the most acute compound eyes in modern arthropods. The specimens show two distinct taphonomic modes, preserved as iron oxide (after pyrite) and calcium phosphate, demonstrating that disparate styles of early diagenetic mineralization can replicate the same type of extracellular tissue (that is, cuticle) within a single Burgess-Shale-type deposit. These fossils also provide compelling evidence for the arthropod affinities of anomalocaridids, push the origin of compound eyes deeper down the arthropod stem lineage, and indicate that the compound eye evolved before such features as a hardened exoskeleton. The inferred acuity of the anomalocaridid eye is consistent with other evidence that these animals were highly mobile visual predators in the water column. The existence of large, macrophagous nektonic predators possessing sharp vision--such as Anomalocaris--within the early Cambrian ecosystem probably helped to accelerate the escalatory 'arms race' that began over half a billion years ago.     

A Cambrian micro-lobopodian and the evolution of arthropod locomotion and reproduction

The evolutionary success of arthropods, the most abundant and diverse animal group, is mainly based on their segmented body and jointed appendages, features that had evolved most likely already before the Cambrian. The first arthropod-like animals, the lobopodians from the Early Cambrian, were unsclerotized and worm-like, and they had unjointed tubular legs. Here we describe the first three-dimensionally preserved Cambrian lobopodian. The material presented of Orstenotubulus evamuellerae gen. et sp. nov. is the smallest and youngest of a lobopodian known. O. evamuellerae shows strikingly detailed similarities to Recent tardigrades and/or onychophorans in its cellular-structured cuticle and the telescopic spines. It also shows similarities to other, longer known lobopodians, but which are ten times as large as the new form. These similarities include the finely annulated body and legs, which is characteristic also for Recent onychophorans, and paired humps continuing into spines situated dorsally to the leg insertions, a feature lacking in the extant forms. The morphology of O. evamuellerae not only elucidates our knowledge about lobopodians, but also aids in a clearer picture of the early evolution of arthropods. An example is the single ventral gonopore between a limb pair of O. evamuellerae, which indicates that a single gonopore, as developed in onychophorans, tardigrades, pentastomids, myriapods and insects, might represent the plesiomorphic state for Arthropoda, while the paired state in chelicerates and crustaceans was convergently achieved. Concerning life habits, the lateral orientation of the limbs and their anchoring spines of the new lobopodian imply that early arthropods were crawlers rather than walkers.     

An armoured Cambrian lobopodian from China with arthropod-like appendages

Cambrian fossil Lagerst?tten preserving soft-bodied organisms have contributed much towards our understanding of metazoan origins. Lobopodians are a particularly interesting group that diversified and flourished in the Cambrian seas. Resembling 'worms with legs', they have long attracted much attention in that they may have given rise to both Onychophora (velvet worms) and Tardigrada (water bears), as well as to arthropods in general. Here we describe Diania cactiformis gen. et sp. nov. as an 'armoured' lobopodian from the Chengjiang fossil Lagerst?tte (Cambrian Stage 3), Yunnan, southwestern China. Although sharing features with other typical lobopodians, it is remarkable for possessing robust and probably sclerotized appendages, with what appear to be articulated elements. In terms of limb morphology it is therefore closer to the arthropod condition, to our knowledge, than any lobopodian recorded until now. Phylogenetic analysis recovers it in a derived position, close to Arthropoda; thus, it seems to belong to a grade of organization close to the point of becoming a true arthropod. Further, D. cactiformis could imply that arthropodization (sclerotization of the limbs) preceded arthrodization (sclerotization of the body). Comparing our fossils with other lobopodian appendage morphologies--see Kerygmachela, Jianshanopodia and Megadictyon--reinforces the hypothesis that the group as a whole is paraphyletic, with different taxa expressing different grades of arthropodization.     

A palaeontological solution to the arthropod head problem

The composition of the arthropod head has been one of the most controversial topics in zoology, with a large number of theories being proposed to account for it over the last century. Although fossils have been recognized as being of potential importance in resolving the issue, a lack of consensus over their systematics has obscured their contribution. Here, I show that a group of previously problematic Cambrian arthropods from the Burgess Shale and Chengjiang faunas form a clade close to crown-group euarthropods, the group containing myriapods, chelicerates, insects and crustaceans. They are characterized by modified or even absent endopods, and two pre-oral appendages. Comparison with reconstructions of the crown-group euarthropod ground plan and recent investigations into onychophorans demonstrates that these two appendages are the first antenna (of extant crustaceans) and a more anterior appendage associated with an ocular segment. The latter appendage has been reduced in all crown-group euarthropods. Its most likely relic is as a component of the labrum. These fossils thus tie together results from disparate living groups (onychophorans and euarthropods).     

Arthropod trace fossils from the Zhujiaqing Formation (Meishucunian, Yunnan) and their palaeobiological implications

1　Biostratigraphicbackgroundandgeologi calsettingIneasternYunnan ,thesupra tointertidaldolomitesoftheXiaowaitoushanMember (Upper mostDengyingFormation =LatestSinian)areun conformablyoverlainbythesubsequent (earliestCambrian) phosphoritesoftheZhujiaqingFormation(MeishucunianStage) .TheoutcropsnearMeishucuninJinningCounty ,southwestofKunmingrepresentsakeysectionforthePC/CtransitionontheYangtzeplatform[1] .TheZhujiaqingFormationbelongstotheEarlytoMiddleMeishucunian (=Nemakit DaldynSt…     

An epipodite-bearing crown-group crustacean from the Lower Cambrian

Crown-group crustaceans (Eucrustacea) are common in the fossil record of the past 500 million years back to the early Ordovician period, and very rare representatives are also known from the late Middle and Late Cambrian periods. Finds in Lower Cambrian rocks of the Phosphatocopina, the fossil sister group to eucrustaceans, imply that members of the eucrustacean stem lineage co-occurred, but it remained unclear whether crown-group members were also present at that time. 'Orsten'-type fossils are typically tiny embryos and cuticle-bearing animals, of which the cuticle is phosphatized and the material is three-dimensional and complete with soft parts. Such fossils are found predominantly in the Cambrian and Ordovician and provide detailed morphological and phylogenetic information on the early evolution of metazoans. Here we report an Orsten-type Konservat-Lagerst?tte from the Lower Cambrian of China that contains at least three new arthropod species, of which we describe the most abundant form on the basis of exceptionally well preserved material of several growth stages. The limb morphology and other details of this new species are markedly similar to those of living cephalocarids, branchiopods and copepods and it is assigned to the Eucrustacea, thus representing the first undoubted crown-group crustacean from the early Cambrian. Its stratigraphical position provides substantial support to the proposition that the main cladogenic event that gave rise to the Arthropoda was before the Cambrian. Small leaf-shaped structures on the outer limb base of the new species provide evidence on the long-debated issue of the origin of epipodites: they occur in a set of three, derive from setae and are a ground-pattern feature of Eucrustacea.     

Sophisticated particle-feeding in a large Early Cambrian crustacean

Most Cambrian arthropods employed simple feeding mechanisms requiring only low degrees of appendage differentiation. In contrast, post-Cambrian crustaceans exhibit a wide diversity of feeding specializations and possess a vast ecological repertoire. Crustaceans are evident in the Cambrian fossil record, but have hitherto been known exclusively from small individuals with limited appendage differentiation. Here we describe a sophisticated feeding apparatus from an Early Cambrian arthropod that had a body length of several centimetres. Details of the mouthparts resolve this taxon as a probable crown-group (pan)crustacean, while its feeding style, which allowed it to generate and handle fine food particles, significantly expands the known ecological capabilities of Cambrian arthropods. This Early Cambrian record predates the major expansions of large-bodied, particle-handling crustaceans by at least one hundred million years, emphasizing the importance of ecological context in driving adaptive radiations.     

Lower Cambrian yolk-pyramid embryos from Southern Shaanxi, China

TheCambrianexplosioniswidelyacceptedasthesuddenappearanceofnumerousbilateriananimalphylaatornearthebeginningofCambriantime[1,2 ] .The 5 30 million year oldMaotianshanShalefaunacontainstheoldestgoodwhole bodyfossilsofbilateri ans,documentinganincreasingnumberofpresent dayanimalphyla[3,4 ] orsubphyla[5] (evenincludingvertebrates[6～ 8] aswell)knownfromLowerCambri an .ThebeginningoftheCambrianperiodisdatedat5 43millionyearsago ,whenthefirstlargeandelabo ratefossilburrowstogetherwiththemicrosco…     

Skara hunanensis a new species of Skaracarida (Crustacea) from Upper Cambrian (Furongian) of Hunan, south China

The fossils of Orsten-type preservation are as famous as Chengjiang Fauna in the world, but it was not until 2005 that the Orsten-type fossils represented by Skaracarida and Phosphatocopida were first reported to be found in western Hunan, South China. Here, we report the systematic paleontology of all the exquisitely preserved specimens belonging to Skaracarida. They were found at a same horizon of Upper Cambrian (Furongian) in Wangcun section, western Hunan, south China, assigned to a new species Skara hunanensis herein. Skara hunanensis is characterized by small, soft-integumented, marine forms with slender, annulate body; labrum large and ventrocaudally directed; uniramous antennulae; biramous antennae and mandibulae; maxillas and maxillipeds of the same shape; all postantennular limbs join a short cephalic filter apparatus. The body has two tagmata: a cephalon with five pairs of well developed appendages and a trunk composed of 11 ring-shaped conical segments.     

Modern optics in exceptionally preserved eyes of Early Cambrian arthropods from Australia

Despite the status of the eye as an "organ of extreme perfection", theory suggests that complex eyes can evolve very rapidly. The fossil record has, until now, been inadequate in providing insight into the early evolution of eyes during the initial radiation of many animal groups known as the Cambrian explosion. This is surprising because Cambrian Burgess-Shale-type deposits are replete with exquisitely preserved animals, especially arthropods, that possess eyes. However, with the exception of biomineralized trilobite eyes, virtually nothing is known about the details of their optical design. Here we report exceptionally preserved fossil eyes from the Early Cambrian (～ 515 million years ago) Emu Bay Shale of South Australia, revealing that some of the earliest arthropods possessed highly advanced compound eyes, each with over 3,000 large ommatidial lenses and a specialized 'bright zone'. These are the oldest non-biomineralized eyes known in such detail, with preservation quality exceeding that found in the Burgess Shale and Chengjiang deposits. Non-biomineralized eyes of similar complexity are otherwise unknown until about 85 million years later. The arrangement and size of the lenses indicate that these eyes belonged to an active predator that was capable of seeing in low light. The eyes are more complex than those known from contemporaneous trilobites and are as advanced as those of many living forms. They provide further evidence that the Cambrian explosion involved rapid innovation in fine-scale anatomy as well as gross morphology, and are consistent with the concept that the development of advanced vision helped to drive this great evolutionary event.     

New anomalocardid frontal appendages from the Guanshan biota, eastern Yunnan

Anomalocaridids were large predators of the Cambrian seas at the top of the trophic pyramid. Complete anomalocaridid specimens have been rarely discovered and the rigid isolated frontal appendages and mouthparts are more commonly preserved. Here we study new material of the frontal appendages from the Wulongqing Formation, Cambrian Stage 4, Series 2 near Kunming, eastern Yunnan. Two new forms of anomalocaridid frontal appendages are described, namely Anomalocaris kunmingensis sp. nov. and Paranomalocaris multisegmentalis gen. nov., sp. nov. The frontal appendage of A. kunmingensis sp. nov. probably comprises 15 podomeres of which the first one has a weakened skeletoned, the second one is armed with small spines, and the third one is armed with remarkably robust proximal ventral spines with 6 anisomerous auxiliary spines; paired auxiliary spines are associated with podomeres 4–14; podomeres 12–14 are armed with paired dorsal spines, and the last podomere bears 2 distal spines, one spine distinctly larger than the other. The frontal appendage of P. multisegmentalis tapered backwards, consisting of 22 visible podomeres; the most ventral spine is armed with 5 pairs of auxiliary spines, and podomeres 12–21 bear dorsal spines, the last podomere with 2 small distal spines. The new material provides additional evidence for our understanding of the diversity of anomalocaridids in the Cambrian. The morphology of these new finds may indicate the importance of different feeding strategies of anomalocaridids in the Cambrian ecosystem.     

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

The taxonomy of an early ancestor of Recent Priapulidae, Xiaoheiqingella peculiaris (= Yunnanpriapulus halteroformis Huang et al., 2004) from the Early Cambrian Chengjiang fossil Lagerstaette, 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 of Xiaoheiqingella, 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.     

Cambrian origins and affinities of an enigmatic fossil group of arthropods

Euthycarcinoids are one of the most enigmatic arthropod groups, having been assigned to nearly all major clades of Arthropoda. Recent work has endorsed closest relationships with crustaceans or a myriapod-hexapod assemblage, a basal position in the Euarthropoda, or a placement in the Hexapoda or hexapod stem group. Euthycarcinoids are known from 13 species ranging in age from Late Ordovician or Early Silurian to Middle Triassic, all in freshwater or brackish water environments. Here we describe a euthycarcinoid from marine strata in Argentina dating from the latest Cambrian period, extending the group's record back as much as 50 million years. Despite its antiquity and marine occurrence, the Cambrian species demonstrates that morphological details were conserved in the transition to fresh water. Trackways in the same unit as the euthycarcinoid strengthen arguments that similar traces of subaerial origin from Cambro-Ordovician rocks were made by euthycarcinoids. Large mandibles in euthycarcinoids are confirmed by the Cambrian species. A morphology-based phylogeny resolves euthycarcinoids as stem-group Mandibulata, sister to the Myriapoda and Crustacea plus Hexapoda.     

The occurrence of the genus Marrella(Trilobitoidea) in Asia

An important discovery in the Kaili Biota has been made recently, and many interesting components from ChengjiangBiota and Burgess Shale Biota have been discovered. Among them Marrella, only known from mid-Middle Cambrian Burgess Shale Biotaof 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 Cam-brian and is significant for the reconstruction of palaeogeography and evolutionary study of early metazoa. In the present paper Marrellasp. is reported for the first time in Asia.