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

Later 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.

Abundant articulated specimens of the oryctocarine trilobite Oryctocarella duyunensis from the lower Cambrian (Stage 4, Series 2) Balang Formation at the Bulin section in western Hunan Province, South China, permit the description of all meraspid degrees. The maximum number of thoracic segments observed in this collection is 11. Meraspid growth was accompanied by progressive and gradual change in overall form, and this animal showed an homonymously segmented trunk with variation in the number of pygidial segments during ontogeny. Such variation permits a variety of plausible explanations, but a model of successive instars defined by the number of thoracic segments, and in suborder by the number of pygidial segments, is highly unlikely to explain the growth pattern because it would result in the loss of trunk segments between some instars. Degree-based ontogenetic staging is compatible with the variation observed.

In a recent communication on carbon isotope chemostratigraphy of the uppermost Cambrian strata, it was claimed that the Top of Cambrian Excursion (TOCE) is (1) an undocumented negative δ13Ccarb excursion; (2) ambiguously defined; (3) deliberately fictitious or, in the authors’ words, a ‘nihilartikel’; and (4) not synonymous with the Hellnmaria–Red Tops Boundary (HERB) Event. As the authors who have been involved in much of the discussion surrounding the TOCE since its introduction and in subsequent clarification, we wish to emphasize that the recent communication overlooks the fact that the TOCE is in fact a well-documented and clearly defined negative δ13Ccarb excursion, and that the term ‘HERB Event’ was originally used informally, without definition or reference data, for a negative δ13Ccarb peak, a peak later shown to occur within the TOCE excursion. Nearly a decade after the TOCE was named, the concept of the HERB Event was modified from a negative δ13Ccarb peak to a negative δ13Ccarb excursion, making it conceptually synonymous with the TOCE excursion. The recently published commentary is misleading and replete with misconceptions, as we discuss here.

New collections of trilobites from the type section of the Parahio Formation in the Parahio Valley, Spiti, and from the Parahio, Karsha, and Kurgiakh formations in the Zanskar Valley, permit biozonation based on material precisely located within measured stratigraphic sections. Specimens preserved in limestone with mild tectonic deformation clarify the features of several Himalayan taxa known previously only from severely deformed specimens preserved in shale. A total of 75 trilobite taxa from the Cambrian of Spiti and Zanskar can be referred, questionably at least, at the generic level or below, and 61 of these are present in our new collections. This new material is assigned with confidence to 29 existing species, and to 12 new species. Three new genera, Haydenaspis, Bhargavia, and Himalisania, are established; new species include Haydenaspis parvatya, Prozacanthoides lahiri, Probowmania bhatti, Xingrenaspis parthiva, X. shyamalae, Bhargavia prakritika, Kaotaia prachina, Gunnia smithi, Sudanamonocarina sinindica, Proasaphiscus simoni, Koldinia odelli, and Torifera jelli. Ten additional Himalayan forms are assigned at the generic level only, and another 11 are questionably assigned to genera or species. The zonation proposed includes 6 zones and 3 levels, including the Haydenaspis parvatya level, the Oryctocephalus indicus level, the Kaotaia prachina Zone, the Paramecephalus defossus Zone, the Oryctocephalus salteri Zone, the Iranoleesia butes level, the Sudanomocarina sinindica Zone, the Lejopyge acantha Zone, and the Proagnostus bulbus Zone. The sections span from the upper part of the informal Stage 4, Series 2 of the Cambrian System, about 511 Ma old, to the Proagnostus bulbus zone of the Guzhangian Stage near the top of Series 3, dated at about 501 Ma. This time interval is represented by about 2000 m of section, which is thick compared to similar intervals elsewhere and is consistent with high rates of sedimentation along the Himalayan margin at the time. The fauna resembles others from equatorial peri-Gondwanaland, with closest similarity to that of South China. It also bears strong affinity to the North China fauna. Juvenile trilobites are described for the first time from India. A new Chinese species, Monanocephalus liquani, is also described.

Many trilobite species of the order Agnostida have short stratigraphic ranges and global distribution in open-marine deposits. They are most abundant and most diverse from about the middle Middle Cambrian to the middle Upper Cambrian where they are proving to be excellent biostratigraphic indices. We describe unusually rich agnostoid faunas of that age from two thick, well-exposed sections, one near Paibi and one near Wangcun, in northwestern Hunan Province, China. All collections are from the Huaqiao Formation, the definition of which is revised and its stratigraphic content is expanded. Most of the fossils are well preserved in dark, laminated, argillaceous carbonates that were deposited in lower slope environments. These are assigned to 76 species and 33 genera. New species described are Agnostus? babcocki, Ammagnostus? cryptus, Ammagnostus histus, Ammagnostus hunanensis, Ammagnostus wangcunensis, Baltagnostus? ambonus, Linguagnostus stenus, Lisogoragnostus hybus, Lisogoragnostus mictus, and Utagnostus songae. Species reassigned in a new generic combination are Ammagnostus laiwuensis (Lorenz, 1906), Glaberagnostus? cicer (Tullberg, 1880), Kormagnostus minutus (Schrank, 1975), and Pseudophalacroma scanense (Westergård, 1946). The subfamily Ammagnostinae öpik, 1967, is elevated to family rank.

The bases of eight agnostoid biozones are defined by the lowest occurrence of a common species having a relatively short stratigraphic range and wide geographic distribution. In ascending order, these zones are named for Ptychagnostus atavus, Ptychagnostus punctuosus, Goniagnostus nathorsti, Lejopyge laevigata, Proagnostus bulbus, Linguagnostus reconditus, Glyptagnostus stolidotus, and Glyptagnostus reticulatus. Each zone is further characterized by an assemblage of agnostoid species that may vary from place to place. By extrapolating from recently published uranium-lead geochronology, we estimate that the average duration of these agnostoid zones was approximately one million years.

Formal division of the Cambrian System into global series and stages is a current project of the International Subcommission on Cambrian Stratigraphy. If the base of an upper Cambrian series of whatever name is selected to correlate closely with the traditional Middle-Upper Cambrian boundary in Europe, we propose the base of the Linguagnostus reconditus Zone in the Wangcun section as a potential Global Standard Stratotype-section and Point (GSSP). Alternatively, if the base of an upper Cambrian series is selected to coincide with the base of the Glyptagnostus reticulatus Zone, we propose the base of that zone in the Paibi section as a potential GSSP.

Restudy of the limestone slab containing the type suite of Arthricocephalus chauveaui Bergeron, 1899 (Trilobita), the type species of Arthricocephalus Bergeron, 1899, shows that specimens of three species, each representing a separate genus, are present on the slab and were likely included in the original concept of the species. Besides A. chauveaui, the slab contains specimens of Oryctocarella duyunensis (Qian, 1961) and Duyunaspis duyunensis Zhang and Qian in Zhou et al., 1977. Bergeron (1899) illustrated one exoskeleton from the type suite of A. chauveaui only and apparently based much of his written description on that specimen. This specimen was clearly intended to be the type specimen of A. chauveaui. Subsequently, Lane et al. (1988) designated another specimen, which was not originally illustrated, as the lectotype, and this specimen is referable to Oryctocarella duyunensis. As revised here, Bergeron’s illustrated specimen should be regarded as the lectotype of A. chauveaui. Such designation stabilizes the concepts of both Arthricocephalus and A. chauveaui. Arthricocephalites Qian in Lu et al., 1974 and Haliplanktos Blaker and Peel, 1997 are regarded as junior synonyms of Arthricocephalus. Oryctocarella Tomashpolskaya and Karpinski, 1961, which was previously regarded as a junior synonym of Arthricocephalus, is revived as a valid genus. Oryctocarella includes a number of species previously assigned to Arthricocephalus. The type species of both Arthricocephalus and Oryctocarella, together with related species, are described on the basis of new material.

The Wa'ergang section in South China has been proposed as a potential Global Stratotype Section and Point (GSSP) for the base of Stage 10, the uppermost stage of the Cambrian System. In this study, high-resolution C-isotopic compositions are reported and we identified three large negative δ13C excursions, namely N1, N2 and N3, at Wa'ergang. The N1 is located just above the First Appearance Datum (FAD) of Lotagnostus americanus, corresponding to the possible base of the Proconodontus posterocostatus conodont Zone. The N2 was identified within the Micragnostus chuishuensis trilobite Zone and the Proconodontus muelleri conodont Zone. The N3 is located in the lowermost part of the Leiagnostus cf. bexelli – Archaeuloma taoyuanense trilobite Zone or Eoconodontus conodont Zone. The N1 and N2 can be correlated with the negative δ13C excursions preceding the Top of Cambrian Carbon Isotope Excursion (TOCE) observed globally. The N3 can be correlated with the TOCE or the HEllnmaria–Red Tops Boundary (HERB) Event. The inter-basinal correlation of N1 and L. americanus strongly supports that the base of Stage 10 may be best defined by the FAD of L. americanus. We also used a box model to quantitatively explore the genesis of the negative δ13C excursions from South China. Our numerical simulations suggest that weathering of the organic-rich sediments on the platform, probably driven by intermittent sea level fall and/or the oxygenation of the Dissolved Organic Carbon (DOC) reservoir in seawater, may have contributed to the generation of the negative δ13C excursions observed in the Stage 10 at Wa'ergang in South China.

Onset of maturity in trilobites is generally considered to occur when the last trunk segment is released into the thorax, marking the start of the holaspid stage. Here we describe striking morphological changes that occur within the holaspid ontogeny of Lonchopygella megaspina Zhou in Zhou et al., 1977, which include the effacement of dorsal furrows, the rapid and complete degeneration of pygidial lateral spines, and the increasing prominence of a pygidial axial spine. These notable changes, which are not coincident with the onset of the holaspid phase, emphasize that the onset of maturity in trilobites should be viewed on a character-by-character basis before assessing whether the exoskeleton as a whole can be described as mature. The holaspid pygidial condition in L. megaspina may represent an intermediate step in an evolutionary transition in the number, form, and allocation of segments in the tsinaniid trunk. Pygidial transition from a dynamically changing complement of segments in the meraspid phase to a static complement in the holaspid phase was accompanied by a marked change in the extent to which segment boundaries defined pygidial structure. Attaining this static complement allowed subsequent pygidial development to emphasize its structure as an integrated unit in which internal segmental boundaries became diffuse, a continuous margin to become prominent, and an elongated terminal spine, first evident at onset of epimorphic growth, to develop allometrically. Trilobite body development suggests that while the segmented construction placed constraints on how morphology varied, the influence of these constraints diminished following completion of thoracic segment construction. Selective premium for a distinct posterior tagma might favor the early ontogenetic acquisition of such a structure, and could have been a driver of the repeated trend toward caudalization witnessed among derived trilobite clades.

Two arthropod specimens assigned to Anabarochilina australis (Hinz-Schallreuter, 1993) from the late middle Cambrian (Guzhangian Stage, Lejopyge acantha Biozone) Karsha Formation, Zanskar Valley, northern India comprise the first record of the Bradoriida from the Himalaya. These Indian specimens cannot be distinguished statistically from other A. australis material based on valve length and height ratios, and differ only slightly in other characters. These observations justify the synonymy of a number of similar forms worldwide that previously have been only questionably attributed to A. australis. The occurrence of the species in Australia, India, Laurentia, and Kazakhstan encompassed an equatorial distribution from approximately 20° north to 20° south during late middle Cambrian time and indicates that A. australis had the ability to disperse across deep ocean basins. Such a distribution is consistent with a planktonic lifestyle. In contrast, other congeneric species of Anabarochilina apparently had more localized occurrence or, in the case of A. primordialis, were distributed across several paleocontinents and climatic zones.

Parablackwelderia is the oldest known stalk-eyed trilobite and thrived during the middle-late Cambrian (Guzhangian Age) in eastern Gondwanaland. the elongated palpebral lobe extends outward and forward from the anterior corner of the cranidium and shows positive allometry, becoming markedly longer and relatively thinner in large specimens. the animal occurred in muddy environments and may have been a predator that burrowed for concealment. Stalked-eyes were independently derived in several trilobite clades, but whenever they appeared were restricted to small numbers of taxa and thus do not appear to have served as a key innovation that promoted extensive diversification of species bearing the structure. the stalk-eyed condition in trilobites has a striking modern analog in the hypercephaly of diopsinid flies, where it is commonly associated with mate recognition and mate selection. We document the first occurrence of Parablackwelderia in Shandong, North China and describe a new species, Parablackwelderia luensis sp. nov.

Faunal data provide critical constraints upon tectonic models, particularly in such areas of extreme structural complexity as the region adjacent to the eastern syntaxis of the Himalaya. Trilobites reported to have been collected from the Yunling collage at Yinchangou, northwestern Yunnan, are here assigned to Kunmingaspis yunnanensis Chang, 1964, and the concept of the genus Kunmingaspis is reconsidered. Although there is debate about to the paleogeographic affinities of the Yunling collage, the apparent presence of this species supports previous arguments for faunal links between the Yangtze platform and the Himalayan margin during Early and Middle Cambrian time. A significant tectonic event of Late Cambrian/Early Ordovician age present in the western central Himalayan margin suggests that the Lhasa block collided with India at that time, but the northward extent of that block remains unclear. The recently discovered Late Cambrian trilobite fauna of Bhutan may hold the key to establishing faunal relationships between the Tethyan Himalaya, Sibumasu, and the Yangtze platform during this interval. No Cambrian sedimentary rocks are yet known from the Lhasa or Qiangtang blocks of Tibet and so there is no direct evidence for the existence of Cimmeria during the Cambrian Period.

Precise biostratigraphic constraints on the age of the Tal Group are restricted to (1) a basal level correlative with the Anabarites trisulcatus–Protohertzina anabarica Assemblage Zone of southwest China, (2) a level near the boundary of the lower and upper parts of the Tal Group correlative with the early Tsanglangpuan Stage (Drepanuroides Zone), and (3) an interval low in the upper part of the Tal Group correlative with later in the Tsanglangpuan Stage (Palaeolenus Zone). These correlations are based on small shelly fossil and trilobite taxa. Other chronostratigraphic constraints include the marked negative δ13C isotopic excursion coincident with the transition from the Krol Group to the Tal Group. This excursion is used as a proxy for the Precambrian–Cambrian boundary in several sections worldwide and, if applied to the Lesser Himalaya, indicates that the boundary is at or just above the base of the Tal Group. The upper parts of the Tal Group may be of middle or late Cambrian age and might form proximal equivalents of sections in the Zanskar–Spiti region of the Tethyan Himalaya. Both faunal content and lithological succession are comparable to southwest China, furthering recent arguments for close geographic proximity between the Himalaya and the Yangtze block during late Neoproterozoic and early Cambrian time. Trilobites from the uppermost parts of the Sankholi Formation from the Nigali Dhar syncline are described and referred to three taxa, one of which, Drepanopyge gopeni, is a new species. They are the oldest trilobites yet described from the Himalaya.