We describe Cavernocypris xiangi sp. nov., the eighth nominated species of the genus, from two localities in Yunnan Province of southwestern China. As a member of Cavernocypris Hartmann, 1964, C. xiangi sp. nov. has short swimming setae on the second antenna, and its left valve overlaps the right valve on the ventral side. It can be distinguished from its congeners by the elongated, conspicuously pitted carapace and large lateral shield of the hemipenis. Along with two other yet unnamed species, we present the first reports of Cavernocypris from China and also the most southerly records of the genus worldwide, significantly expanding its known geographical range. Up to now, five of the eight named Cavernocypris species and the two unnamed members recovered in this study are restricted to East Asia, which could be a hotspot of diversity for the genus. The large morphological variation and the wide, patchy distribution of Cavernocypris imply that diversification in the genus has a long geological history.

Ostracods have frequently been reported as part of the active faunas in the wet phase of rice fields, but knowledge on the dormant ostracods during the dry period of the rice cycle has been limited, hindering a comprehensive understanding of their adaptation to the rice field environment. In this study, we record 11 dormant ostracod species by incubating soil samples from six desiccated rice fields in Yunnan Province of southwestern China. The dormant ostracod community was dominated by species of the family Cyprididae, accompanied by members of Candonidae, Ilyocyprididae, and Notodromadidae. Our data provide unequivocal evidence for the presence of dormant ostracods from all the four families of the superfamily Cypridoidea in desiccated rice fields, verifying that these ostracods adapt to the rice fields by desiccation-resistant stage. Considering the usually shallow penetration depth of ostracods, the frequent discoveries of dormant ostracods in 2‒4 cm depth in the soil profile were probably the result of ploughing. Despite overlap in species composition, the dormant ostracod community differs from the active community sampled at the same sites more than four years ago. This suggests temporal changes of faunal composition, although the ecological memory of the dormant community containing multiple generations and the different seasonal windows represented by the two types of communities should also be considered. The emergence of adults within the first two weeks of the incubation experiment suggests the presence of dormant instars in the soil rather than resting eggs alone.

Pectocaris species are intermediate- to large-sized Cambrian bivalved arthropods. Previous studies have documented Pectocaris exclusively from the Cambrian Series 2 Stage 3 Chengjiang biota in Yu’anshan Formation, Chiungchussu Stage in SW China. In this study, we report Pectocaris paraspatiosa sp. nov., and three other previously known Pectocaris from the Xiazhuang section in Kunming, which belongs to the Hongjingshao Formation and is a later phase within Cambrian Stage 3 than the Yu’anshan Formation. The new species can be distinguished from its congeners by the sparsely arranged endopodal endites and the morphologies of the abdomen, telson, and telson processes. We interpret P. paraspatiosa sp. nov. as a filter-feeder and a powerful swimmer adapted to shallow, agitated environments. Comparison among the Pectocaris species reinforces previous views that niche differentiation had been established among the congeneric species based on morphological differentiation. Our study shows the comprehensive occurrences of Pectocaris species outside the Chengjiang biota for the first time. With a review of the shared fossil taxa of Chengjiang and Xiaoshiba biotas, we identify a strong biological connection between the Yu’anshan and Hongjingshao Formations.

Previous studies of the Recent non-marine ostracods of Yunnan Province in southwestern China yielded 42 species, among which only 18 species were reported based on living material. Such a low number is likely to underestimate the species diversity of ostracods in Yunnan, considering the geographical disparity among its different parts. In this study, we report 11 nominal species and one species left in open nomenclature from 22 samples collected from the Kunming area in eastern-central part of Yunnan. Among these species, seven are new to the province, including Notodromas semiovata n. sp., Chrissia acuminata n. sp., and the first records of the male of Cypridopsis vidua (O.F. Müller, 1776) outside the USA. A review of previous literature indicates that, with the exception of the two new species, all the other 23 species have Palaearctic (PA) distributions, while only 14 have Oriental (OL) distributions. Such a composition contradicts previous vertebrate-based zoogeographical subdivisions of China in which Yunnan was included in the OL region, and adds to the argument that the geographical distributions of various invertebrate groups need to be investigated to map the PA‒OL boundary in China more appropriately.

Early euarthropod evolution involved a major transition from lobopodian-like taxa to organisms featuring a segmented, well-sclerotized trunk (arthrodization) and limbs (arthropodization). However, the precise origin of a completely arthrodized trunk and arthropodized ventral biramous appendages remain controversial, as well as the early onset of anterior-posterior limb differentiation in stem-group euarthropods. New fossil material and micro-computed tomography inform the detailed morphology of the arthropodized biramous appendages in the carapace-bearing euarthropod Isoxys curvirostratus from the early Cambrian Chengjiang biota. In addition to well-developed grasping frontal appendages, I. curvirostratus possesses two batches of morphologically and functionally distinct biramous limbs. The first batch consists of four pairs of short cephalic appendages with robust endites with a feeding function, whereas the second batch has more elongate trunk appendages for locomotion. Critically, our new material shows that the trunk of I. curvirostratus was not arthrodized. The results of our phylogenetic analyses recover isoxyids as some of the earliest branching sclerotized euarthropods, and strengthens the hypothesis that arthropodized biramous appendages evolved before full body arthrodization.

Lake sediments that widely distributed in the active and complicated fault zones have been recently showing great potential for paleoseismic reconstruction. However, flood events and human activities may make the seismic signal unrecognizable. In this study, high-resolution analyses of sedimentary structure, physical and chemical proxies, as well as absolutely radioactive dating were conducted on seven representative sediment cores from the depocenter, nearshore and inlet areas of Yangzong Lake, a typical fault lake in the Xiaojiang Fault zone, southeastern Tibetan Plateau (TP). These new data were calibrated by historical documents, suggesting that seismically induced mass-transport deposits (MTDs, i.e., turbidites) were massive and/or amalgamated (earthquake doublet), became fining and thickening towards the lake center (without changing lake morphology), and occasionally exhibited soft sediment deformation structures (SSDs, i.e., microfaults). These sediments were relatively poorly sorted and instantaneously deposited from slope failures within the lake. An extremely strong earthquake could cause coseismic subsidence of the lake basin and destruct the local hydrological system, resulting in exceptionally high Mn and total inorganic carbon (TIC) contents in the lake center. In contrast, flood deposits were thinner with horizontal beddings, had higher terrestrial organic matter (higher C/N ratios), and distributed locally in the lake inlet area. Human activities-induced sediments were inversely graded, poorly sorted and gradually deposited, had horizontal beddings and no erosive base, and exhibited high carbon, Pb and Zn contents and low C/N ratios. In addition, macroseismic investigations and statistical results from intensity prediction equations (IPEs) provided a conservative threshold of ∼8 Modified Mercalli Intensities (MMI) for triggering turbidites, and a ∼ 10 MMI for inducing coseismic subsidence and hydrological destruction. This study was among the first attempts to establish a quantitative lacustrine paleoseismograph in the southeastern TP, and the new results would greatly improve the valid assessment of geohazard risks.

Dynamic mechanical analysis offers the opportunity to explore the motility and feeding strategies of extinct organisms, but the prerequisite is to have an accurate recovery engineering model. As shown with micro-computed tomography (CT) scanning, fossils of the bivalved arthropod Ercaicunia multinodosa from the Cambrian (Series 2, Stage 3) Chengjiang biota of China have well-preserved three-dimensional (3D) morphological details with a certain degree of compression. Here, we propose a palaeontological restoration method using computational fluid dynamics (CFD) to analyse multiple hypothetical models based on the fossil information to obtain a reasonable restoration model. Furthermore, we carry out hydrodynamic experiments to verify the palaeontological restoration results. Our simulation and experimental results suggest that, a dorsally convex and ventrally straight body shape with the valves opening at an angle of approximately 120° works best for E. multinodosa to overcome resistance, and in the meantime obtain most lift while sliding in the water column. The combination of three-dimensional reconstruction, CFD simulation, and hydrodynamic experiments provides a useful method for restoring the morphologies of extinct animals and exploring their palaeoecology.

Despite previous scientific investigations on the limnic ostracods in eastern Inner Mongolia, the ostracod assemblages in aquatic habitats other than the large brackish lakes in this region have been poorly studied, hampering comprehensive knowledge of the regional ostracod fauna. Here we analyze the ostracod assemblages in various surface waters in central-eastern Inner Mongolia, including the abundant ponds formed due to road construction that are otherwise rare on the grassland, as well as natural swamps, lakes, and running waters. A total of 19 species of living ostracods are recovered, with the ponds dominated by Heterocypris incongruens and Ilyocypris mongolica, swamps by Physocypria kraepelini, lakes by Limnocythere inopinata and I. mongolica, and running waters hosting fewer ostracods. Comparative study of the ostracod assemblages from different areas in China and Mongolia reveals intermediate to strong degree of ecological disturbance of the aquatic habitats in central-eastern Inner Mongolia, as denoted by the prevalence of the ecologically tolerant widespread species H. incongruens, L. inopinata, and P. kraepelini. We propose that the ecological disturbance of the aquatic habitats in this area originates from both artificial and natural factors: the flourishment of H. incongruens and P. kraepelini reflect unstable and polluted environments due to human activities including road constructing and livestock raising, while the ubiquity of L. inopinata is due to enriched and fluctuating water chemistry under semi-arid climate. The endemic ostracods in central-eastern Inner Mongolia show sporadic occurrence, and future conservation of these species should be focused on the sites that possess favourable ecological niches.

Micro-CT scanning reveals unprecedented three-dimensional soft anatomy of the early Cambrian (Epoch 2, Age 3) euarthropod Chuandianella ovata.We interpret the presence of an elongate, antenniform first appendage, and a short uniramous second appendage, followed by 10 homonomous biramous appendages comprising a short paddle-shaped exopod and a unique feather-like limb-branch with at least 27 podomeres each of which bears a long blade-like endite with a short terminal seta: we interpret this as the endopod.Alternative interpretations, that these limbs might represent an epipod+basipod or epipod+exopod arrangement, are unlikely, in that they would require either the complete reduction of the exopod or the endopod.We also find no evidence for head appendage morphologies that would support a more crownward position, for example among pancrustaceans, that has previously been suggested for C. ovata.

SUMMARYThe Cambrian Stage 3 Chengjiang biota in South China is one of the most influential Konservat-Lagerstätten worldwide thanks to the fossilization of diverse non-biomineralizing organisms through pyritization. Despite their contributions to understanding the evolution of early animals, several Chengjiang species remain poorly known due to their scarcity and/or incomplete preservation. Here, we use micro-computed tomography to reveal in detail the ventral appendage organization of the enigmatic non-trilobite artiopodPygmaclypeatus daziensis– one of the rarest euarthropods in Chengjiang – and explore its functional ecology and broader evolutionary significance.Pygmaclypeatus daziensispossesses a set of uniramous antennae and 14 pairs of post-antennal biramous appendages, the latter of which show an unexpectedly high degree of heteronomy based on the localized differentiation of the protopodite, endopodite and exopodite along the antero-posterior body axis. The small body size (less than 2 cm), presence of delicate spinose endites, and well-developed exopodites with multiple paddle-shaped lamellae on the appendages ofP. daziensisindicate a nekto-benthic mode of life, and a scavenging/detritus feeding strategy.Pygmaclypeatus daziensisshows that appendage heteronomy is phylogenetically widespread within Artiopoda – the megadiverse clade that includes trilobites and their relatives with non-biomineralizing exoskeletons – and suggests that a single exopodite lobe with paddle-like lamellae is ancestral for this clade.Abstract FigureCover image:Morphological reconstruction of the non-trilobite artiopodPygmaclypeatus daziensisfrom the early Cambrian (Stage 3) Chengjiang biota in south China. Artwork by Holly Sullivan (https://www.sulscientific.com/).

Three new species, Pseudocandona cheni sp. nov., Cyclocypris pangi sp. nov., and Tonnacypris rectangularis sp. nov., collected from northern China, are described in this study. Pseudocandona cheni, of the compressa group, is difficult to be distinguished from other members of the same group by carapace morphology alone, but can be readily recognised by the structure of the hemipenis comprised of a long lobe a, distally inflated lobe h, and exteriorly pointed lobe b, as well as thick trunks of the male fifth limb endopodites. Cyclocypris pangi, despite its similarity in carapace morphology to its congeners, can be identified based on the morphology of the hemipenis, which bears a slender, slightly curved lobe h, and an S-shaped process accompanying lobe b, in addition to the rectangular trunk of the male fifth limb endopodite. On the other hand, Tonnacypris rectangularis, described on the basis of females only, can be distinguished from other Tonnacypris Diebel & Pietrzeniuk, 1975 representatives by its distinct sub-rectangular carapace alone. Other differences include the length of the swimming setae, the length of the distal claws on the second an-tennae, and the morphology of the pincer organ on the seventh limb. This study contributes to the poorly known extant non-marine ostracod fauna of Inner Mongolia and Beijing, and generally to the central-eastern Palaearctic region. In addition, the known distribution range of Tonnacypris is extended eastwardly by T. rectangularis. The valve-morphology data are useful for identifying fossil/sub-fossil representatives.

Limnocythere inopinata (Baird, 1843) is a widely distributed ostracod in modern non-marine waters and Quaternary sediments. Based on its morphological variation (the number and position of its nodes), different phenotypes have been identified. However, the factors controlling its morphological variation are currently open to debate, which hinders palaeoecological reconstructions based on this species. In this study, ostracod distribution and hydrochemical analyses of the ambient environment of 21 lakes in the Badain Jaran Desert were carried out. Three ostracod species belonging to two genera are identified as Limnocyhtere inopinata, Cypris cf. granulate and Cypris sp. with the dominant species L. inopinata represented by six phenotypes. The distribution features of these ostracods in the lakes and related ecological information are reported. In addition, the factors controlling the morphological variations of L. inopinata were analysed. Our data indicate that the noded individuals of L. inopinata prefer water with appropriate Ca2+ content (30–40 mg L−1) and low salinities (below 4.60 g L−1). The percentage of noded individuals of L. inopinata increases with increasing salinity only within a certain salinity range. Hence, caution should be exercised in reconstructions of palaeosalinity based on the morphological variability of L. inopinata.

Ilyocypris leptolinea Wang & Zhai, sp. nov. is described from late Quaternary sediments in central-eastern Inner Mongolia, northern China. The new species, which has a carapace shape and pitted surface typi-cal of the genus, is characterised by double rows of fine, densely arranged marginal ripplets, separated by an inner list, along both anterior and posterior calcified inner lamellae in the left valve. Outline analysis and Principal Component Analysis indicate that its morpho-space overlaps with I. bradyi Sars, 1890, I. japonica Okubo, 1990, and I. mongolica Martens, 1991, which have living or fossil representatives in Inner Mongolia, but it is clearly discriminated from I. innermongolica Zhai & Xiao, 2013. Judging from the relatively coarse lithology dominated by silt and sand, and the lack of accompanying brackish-water ostracods, I. leptolinea Wang & Zhai, sp. nov. may have lived in a relatively shallow freshwater lake. It perhaps can be added to the list of species that went extinct during the Quaternary, but the timing and process of extinction await further investigation.

We analyze 31 surface-sediment samples from the depths of 2–33 m in the large fresh-water Lake Ngoring on the northeastern Tibet–Qinghai Plateau to provide depth-preference information of ostracods valuable for palaeo-bathymetric reconstruction. Among the nine species discovered, Tonnacypris estonica and Ilyocypris echinata show clear preferences to shallow waters while Leucocythere sp. 1 and Cytherissa lacustris are confined to depths exceeding 22 m. Ilyocypris sp., Candoninae sp., and Leucocythere sp. 2 are slightly more abundant in deeper parts of the lake, while Candona candida and Fabaeformiscandona sp. tend to be more abundant in the shallow area. Such information can be used to reconstruct qualitatively the past lake level. Meanwhile, based on 23 forward-selected samples with over 200 valve counts, three water-depth transfer functions are established, which have generally good and comparable performances judged from their determination coefficients and predictive errors. We propose that future studies should endeavor to investigate the distribution of more ostracod species across wider depth ranges from various lakes to encompass the large changes in ostracod assemblage and depth in the geologic past, and that datasets from different lakes can be synthesized into 'mega-transfer functions' to improve palaeolimnological reconstruction.

Although first described in 1999, the early Cambrian Pectocaris remains a poorly known euarthropod genus. Two species, Pectocaris eurypetala and P. spatiosa , have been described from the Chengjiang biota. Here, we report a third species, Pectocaris inopinata sp. nov., which bears a pair of stalked eyes attached to an anterior sclerite, a pair of short but stout antennae, 29–35 cephalothoracic segments each corresponding to a pair of biramous appendages, 11–12 limbless segments carrying two rows of ventral spines and one row of dorsal spines, and a pair of broad telson flukes decorated with short marginal spines. Most strikingly, the endopods of anterior trunk appendages are each axially differentiated with two rows of setulose endites proximally and claw‐like paired spines distally, in contrast to the endopods of posterior trunk appendages that carry two rows of setulose endites but lack claw‐like paired spines. Phylogenetic analysis shows that P. inopinata , the other two Pectocaris species, together with their close relative Jugatacaris agilis belong to the same monophyletic clade. Our study reveals considerable differences in appendicular details and therefore presumably niche differentiation among Pectocaris and Jugatacaris species, as well as some other bivalved euarthropods in the Cambrian with similar overall appearances.