Abstract We present a detailed exploration of the growth and segmentation of the proasaphiscid trilobite Maotunia iddingsi from the middle Cambrian (Miaolingian, Drumian), North China, and investigate morphological variation and modification of the developmental patterning within the Ptychopariida. The full ontogenetic sequence, which exhibits a complex situation regarding segment expression and liberation, provides evidence of a marked intraspecific variation in somitogenesis and tagmosis during the whole life cycle. The progressive release of trunk segments may have varied among individuals, indicating a potential developmental plasticity and life strategy by which early diversified trilobites could control the proportion of head to trunk in size during the life cycle.

An investigation of growth and segmentation of a ptychopariid trilobite Maotunia iddingsi from the middle Cambrian (Miaolingian, Drumian) Zhangxia Formation, North China is presented. This is the first time the essentially complete post-embryonic ontogenetic series from protaspid to holaspid period based on numerous articulated specimens is clearly demonstrated and reported as a ptychopariid representative. The full post-embryonic developmental sequence, which exhibited a heteronomous trunk segment condition and an unbalanced rate in segment expression and liberation during ontogeny, witnessed a marked intraspecific variation in somitogenesis and tagmosis during the life cycle. The progressive release of the trunk segments may vary at rates among different individuals, revealing a potential developmental strategy how early diversified arthropods controlled the form of the body patterning as well as the proportion of head to trunk in size during the enrollment process of its life cycle. (c) 2025 Elsevier B.V. and Nanjing Institute of Geology and Palaeontology, CAS. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

A new species of damesellid trilobite, Bergeronites leishuae n. sp., is described from the Fulu Biota in the Longha Formation (Cambrian, Guzhangian), southeastern Yunnan Province, South China. Bergeronites leishuae is common in the Fulu Lagerstatte and represented by both disarticulated sclerites and the first complete exoskeletons recorded for the genus. Together, these remains allow for a more thorough understanding of the morphology of this distinctive trilobite genus, both dorsally and ventrally. The new material also allows for further differential comparisons with other species previously assigned to Bergeronites. Specimens showing the ventral cephalic morphology reveal the presence of a short connective suture immediately flanking the sagittal line of the doublure, and a thin, ridge-like rostral plate. They also show the hypostome to be in conterminant condition. Ontogenetic material of B. leishuae is known from meraspid degree 6 through the holaspid stage; it includes the first meraspid-stage specimens known for Bergeronites. As presently known, the geographic distribution of Bergeronites is restricted to the East Asian sector of Gondwana (North China, South China, and Vietnam). (c) 2025 Elsevier B.V. and Nanjing Institute of Geology and Palaeontology, CAS. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

Vetulicolians are an enigmatic phylum of extinct Cambrian marine invertebrates. They are particularly diverse in the Chengjiang Biota of China, but representatives have been recovered from other Fossil-Lagerstätten (Cambrian Stage 3-Drumian). These organisms are characterized by a bipartite body, which is split into an anterior section and a posterior segmented section connected by a narrow constriction. Here we report new material of the genus Pomatrum from the Cambrian Balang Biota (Series 2, Stage 4) of Hunan, southern China. This is the first discovery of this vetulicolian outside of the Chengjiang Biota (Series 2, Stage 3) and the first report of vetulicolians from the Balang Biota. This finding not only suggests that this group had a wider spatial and temporal distribution than previously known, but also adds information to the overall biodiversity of the Balang Biota—one of the most important Stage 4 fossil deposits known from Gondwana.

A new dameselloid trilobite, Leishuia leishuae n. gen. n. sp., from the Fulu Biota in the Longha Formation (Cambrian: Guzhangian) in southeastern Yunnan, South China, is described. At least six dameselloid trilobite genera are represented in the Fulu Biota. Leishuia n. gen., Karslanus, and Teinistion show a natant hypostomal condition, whereas Bergeronites, Damesops, and Palaeadotes show a conterminant hypostomal attachment condition. The discovery of two forms of hypostomal attachment in dameselloid trilobites warrants reinterpretation of the classification of the group. A revised classification of the superfamily Dameselloidea is proposed. It includes two families, Damesellidae and Dorypygellidae, and three subfamilies belonging to Damesellidae, Damesellinae, Drepanurinae, and Bergeronitinae n. subfam. The Dameselloidea embraces dameselloids characterized by having a hypostome in conterminant attachment and lacking a preglabellar field; and the Dorypygellidae, which have a hypostome in natant attachment and have a preglabellar field. The new subfamily, Bergeronitinae, is characterized by having macropleural segments in the thorax and pygidium, and a conterminant hypostomal condition.

The trilobite Karslanus Özdikmen, 2009 (replacement name for Ariaspis Wolfart, 1974, preoccupied) is a presumed dameselloid genus reported from Afghanistan and South China. Until now, it has been known only from fragmentary material. A new species, Karslanus leishuae, from the Fulu Biota in the Longha Formation (Cambrian: Guzhangian) of Yunnan, South China, is represented by complete exoskeletons, the first such material recovered for the genus. Karslanus is unusual among dameselloids in having an holaspid thorax of 10 segments; it is also characterized by a pygidium with the pleurae extended into marginal spines that decrease in length rearward and a natant hypostome. This discovery adds to growing evidence that both conterminant and natant hypostomal conditions are represented among taxa in the superfamily Dameselloidea.

Enteropneusts (acorn worms) are hemichordates, the sister group to echinoderms. Together they form the clade Ambulacraria, which is closely related to chordates. All three groups appear in the lower Cambrian, but their interrelationships remain problematic, which impedes the understanding of early deuterostome evolution. Enteropneusts are also extremely rare in the fossil record, only a few species are known from Lagerstatten-type deposits. Here, we describe the earliest known enteromens, including tornaria larvae and juveniles, from the lower Cambrian (Epoch 2, Stage 3) Haiyan Lagerstatte, Chengjiang biota, of China. The enteropneust larvae and post-metamorphic juveniles are the first reported in the fossil record and provide direct evidence for a pelago-benthic lifestyle in a Cambrian deuterostome animal, bolstering the hypothesis that an indirect development is primitive to the enteropneusts and maybe the hemichordates or whole of Ambulacraria.

More than one thousand cranidia, librigenae, and pygidia of the trilobite Pagodia were collected from the Cambrian (upper Jiangshanian through Stage 10) at Fenghuangshan in northern Anhui, China. They were identified as Pagodia lotos Walcott, 1905, Pagodia depressa (Walcott, 1905), and Pagodia bia Walcott, 1905. Based on one rare nearly complete exoskeleton of P. depressa and comparisons among the three species of Pagodia, the redefinition for those species is attempted as follows. Pagodia lotos: Glabella rectangular, slightly convergent anteriorly; anterior border ridge-like, anterior border furrow deep; pygidium semicircular, axis tapered rearward, with 4 axial rings and a terminal piece. P. depressa: Cranidium subquadrate, highly convex; glabella cylindrical, convergent anteriorly; pygidium semicircular. P. bia: Glabella rectangular, constricted in the midlength; fixigena wide (tr.); anterior border very narrow (sag.) and ridge-like; pygidium semicircular with wide borders; pygidial axis ended closer to the pygidial border furrow. We also discuss their intraspecific variations, commonly seen on the exfoliated specimens: palpebral ridge evident or obliterated, the length (sag.) of anterior area variable, the decoration of exoskeleton surface (with granules variable in size, convex or pitted).

The Cambrian Radiation represents one of the largest diversification events in Earth history. While the resulting taxonomic diversity is exceptional, relatively few of these novel species can be traced outside the boundaries of a single palaeocontinent. Many of those species with cosmopolitan distributions were likely active swimmers, presenting opportunity and means to conquer new areas, but this would not have been the case for sessile organisms. Herpetogaster is a lower to middle Cambrian (Series 2–Miaolingian, Stage 3–Wuliuan) genus of sessile, stalked, filter-feeding deuterostomes with two species, H. collinsi and H. haiyanensis, known respectively from Laurentia and Gondwana. Here, we expand the distribution of H. collinsi to Gondwana with newly discovered specimens from the Balang Formation of Hunan, China. This discovery raises questions on the origin of the genus and how sessile organisms were able to disperse over such a broad distance in the lower Cambrian. As Herpetogaster has been recovered at the base of the Ambulacrarian tree in recent phylogenies, a planktonic larval stage is suggested, which implies, that the last common ancestor of the Ambulacraria might have already had planktonic larvae or that such larvae developed multiple times within the Ambulacraria.

The Ediacaran Period marks a pivotal time in geodynamo evolution when the geomagnetic field is thought to approach the weak state where kinetic energy exceeds magnetic energy, as manifested by an extremely high frequency of polarity reversals, high secular variation, and an ultralow dipole field strength. However, how the geodynamo transitioned from this state into one with more stable field behavior is unknown. Here, we address this issue through a high-resolution magnetostratigraphic investigation of the ~494.5 million-year-old Jiangshanian Global Standard Stratotype and Point (GSSP) section in South China. Our paleomagnetic results document zones with rapid reversals, stable polarity and a ~80 thousand-year-long interval without a geocentric axial dipole field. From these changes, we suggest that for most of the Cambrian, the solid inner core had not yet grown to a size sufficiently large to stabilize the geodynamo. This unusual field behavior can explain paleomagnetic data used to define paradoxical true polar wander, supporting instead the rotational stability of the solid Earth during the great radiation of life in the Cambrian.

The North China type Cambrian System is well developed in northern Anhui Province. A large number of specimens of the trilobite Pseudoblackwelderia lubrica were collected from the Guzhangian (later Cambrian) Changhia Formation at Fenghuangshan in northern Anhui, China, prompting a redefinition of the species. Our emended diagnosis includes: a cone-shaped glabella that is broadly to acutely rounded anteriorly; three pairs of glabellar furrows; the preglabellar field being absent or very short; the librigena with a narrow lateral border, a broad general field and long genal spine; the pygidium with four rings and a terminal piece on the axis; six or seven pairs of pygidial spines with the anterior five pairs being short, the posterolateral pair being long and stout, the seventh pair being small or absent. The new specimens suggest that Neimengguasps is a junior synonym of Pseudoblackwelderia. Moreover, the presence or absence of paired spines on the posterior margin of pygidium is attributed to potential sexual dimorphism.

The taxonomy of trilobites Abadiella Hupé, 1953 and Parabadiella Zhang, 1966 from the lower Cambrian of Gondwana has long been a controversy. Based on newly-collected and formerly-reported materials, 94 trilobite cranidia within 21 species are selected for morphometric analyses: principal components analysis (PCA) and canonical variates analysis (CVA). The integrated morphological characters are successfully accounted for by two principal components in PCA. The further validations for the presupposed qualitative groupings are indispensable to detect and calibrate the ultimate taxonomic results in CVA. By this way, all specimens distributed in a consistent morphospace in PCA and the short distances between them demonstrate their close morphological affinity, supporting their congeneric status within Abadiella. Additionally, three morphotypes were recognized from all selected specimens and they were eventually revised and incorporated into A. bourgini Hupé, 1953, A. huoi Zhang, 1966, and A. yunnanensis Luo, 1981, through stepwise test-calibration to get a high correct rate as far as possible in CVA. From this, it is certain that A. huoi is conspecific in South Australia and South China. Its occurrence allows to correlate the Australian A. huoi Range Zone to the identical zone in South China (in platform), having an approximately consistent stratigraphic range in the two regions. In comparison with A. huoi, A. bourgini was reported from fewer localities in South China. Nevertheless, its presence in the Daguinaspis Zone of Issendalenian Stage in Morocco permits a correlation with Chinese and Australian A. huoi Zone. As an auxiliary marker for A. huoi, the occurrence of A. bourgini in Morocco, South Australia and South China reinforce the correlation potential and resolution in species-level for the Cambrian Stage 3 in Gondwana region.

The ontogenetic sequence of an early Cambrian redlichiid trilobite Bathynotus kueichouensis is presented on the basis of numerous articulated specimens from Guizhou, China. The body regionalization of B. kueichouensis witnessed a wide variation in the morphology of trunk segments between different thoracic regions, referred to as the 'thoracic region 1-4'. A greater size variation of these long pleural spines is recognized from the earlier meraspid degrees in a gradual appearance or disappearance until the holaspid period. The thoroughly inverse variation of these pleural spines in size and form is seen for the first time during the process of trilobite segment formation, which offers an opportunity to trace the evolutionary path of trilobite body structures, associated with their functional morphology and behavior. The ontogenetic strategy of B. kueichouensis is broadly similar to those of other redlichioid representatives where the full ontogenetic sequence exhibited a balanced rate in segment expression and liberation. Such a developmental mode may be the reason why most redlichiids possess a micropygous body patterning during ontogeny and provides insights into the controls of early arthropod developmental segmentation during evolutionary process.

AbstractLater Cambrian and earliest Ordovician trilobites and brachiopods spanning eight horizons from five localities within the Sông Mã, Hàm Rồng and Đông Sơn formations of the Thanh Hóa province of Việt Nam, constrain the age and faunal affinities of rocks within the Sông Đà terrane, one of several suture/fault-bounded units situated between South China to the north and Indochina to the south. ‘Ghost-like’ preservation in dolomite coupled with tectonic deformation leaves many of the fossils poorly preserved, and poor exposure precludes collecting within continuously exposed stratigraphic successions. Cambrian carbonate facies pass conformably into Lower Ordovician carbonate-rich strata that also include minor siliciclastic facies, and the recovered fauna spans several uppermost Cambrian and Lower Ordovician biozones. The fauna is of equatorial Gondwanan affinity, and comparable to that from South China, North China, Sibumasu and Australia. A new species of Miaolingian ‘ptychopariid’ trilobite,Kaotaia xuanensis, is described. Detrital zircon samples from Cambrian–Ordovician rocks of the North Việt Nam and Sông Đà terranes, and from Palaeozoic samples from the Trường Sơn sector of Indochina immediately to the south, contain a predominance of ages spanning the Neoproterozoic period and have a typical equatorial Gondwanan signature. We associate the Cambrian and Tremadocian of the Sông Đà terrane with areas immediately to the north of it, including the North Việt Nam terrane and the southern parts of Yunnan and Guangxi provinces of China.

The developmental mode of four redlichiid trilobites is summarized, based upon exceptionally well-preserved, articulated specimens from Cambrian Series 2 (stages 3 and 4) strata in southwestern China and South Australia. These relatively complete developmental sequences indicate a balanced rate in segment increase and addition to the thorax during the meraspid phase, which might explain why most redlichiids possess micropygous body patterning during ontogeny. In addition, an analysis of the size distribution, developmental strategy, and distribution of specimen numbers at different growth stages reveals a distinct developmental strategy during the redlichiid life cycle. A relatively short pre-holaspid and a prolonged holaspid phase in these redlichiid taxa offers insight into the developmental control and life strategy in these primitive arthropods.

The trilobite Liostracina has been recognized as important in taxonomic and stratigraphic studies for more than a century. Until now, the genus Liostracina and family Liostracinidae have been known from only incomplete holaspid material, a degree 2 meraspis, and protaspides. A new locality in the Longha Formation (Cambrian: Guzhangian) of southeastern Yunnan, China, yields a rich collection of articulated holaspid exoskeletons and disarticulated sclerites of a new species, Liostracina fuluensis n. sp. These specimens reveal thoracic and ventral morphology that was previously unknown for Liostracina ; they demonstrate that it has a rostral plate plus rostral and connective sutures, rather than a ventral median suture on the cephalic doublure. This confirms a natant hypostomal condition for the genus. Holaspid exoskeletal features, combined with evidence of a non-asaphoid-type protaspis, indicate that Liostracina is neither a primitive trinucleoid nor a primitive asaphoid. The family Liostracinidae is excluded from the superfamily Trinucleoidea and the order Trinucleida and reassigned to the order Ptychopariida. UUID: http://zoobank.org/48dcbe31-e25d-4657-8441-732d5ea2b49d