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The age of the Silurian “Lower Red Beds” (LRBs), which occur widely in South China, has long been controversial because of the scarcity of index fossils. Here, we report a fauna with abundant trilobites from the LRBs in Wuhan, Middle Yangtze region, consisting of Aulacopleura (Paraaulacopleura) pijiazhaiensis, ‘Encrinuroides’ yichangensis, Gaotania hubeiensis, Hyrokybe gaotanensis, Japonoscutellum yichangense, Latiproetus latilimbatus, and Ptilillaenus lojopingensis. These trilobites are common in the Leijiatun, upper Xiangshuyuan, Shihniulan, and Lojoping formations in the Upper Yangtze region, and belong to the middle to upper Aeronian Ptilillaenus or ‘Encrinuroides’–Ptilillaenus–Latiproetus assemblages. The discovery of this trilobite assemblage suggests that the LRBs are probably partly of middle–late Aeronian age in the Middle Yangtze region. Thus, the lower boundary of the LRBs is likely diachronous in the Yangtze region, ranging from the middle–late Aeronian to the early Telychian. The discovery of the Ptilillaenus assemblage in the Wuhan LRBs expands the paleogeographic distribution of this assemblage and provides evidence of deeper depositional environment of the LRBs in the study area versus shallow waters in other areas of the Yangtze region.

Malformations are common in trilobites, but the majority of described specimens are from Europe and North America. Only a few abnormal trilobites have been reported from China. Ten abnormal trilobites from Cambrian, Ordovician and Silurian strata in central and eastern China are documented. The abnormal Ordovician trilobites are found for the first time in China. All malformations occur in the thoraxes and pygidia, and were caused by a sub-lethal predatory attack, genetic or embryological malfunction, or injury sustained during molting. It is difficult to identify the predators of the six injured trilobites, but potential predators include Cambrian non-trilobite arthropods, Ordovician cephalopods, and Silurian eurypterids, chondrichthyes or cephalopods, even cannibalistic trilobites. Abnormal specimens caused by sub-lethal predatory attacks mainly occur in Cambrian strata in China and other areas in the world, and are very rare in post-Cambrian strata. This pattern may reflect the rise of predators and increased predation in the post-Cambrian, which led to an increased trilobite fatality rate, thus reducing the probability that injured specimens would become fossilized.

Trace fossils are special objects in the study of predator–prey interactions in the fossil record. Here we report on diverse morphological types of the gnathostome fish hunting trace Osculichnus from the Upper Devonian of South China. The studied Osculichnus specimens occur as groups of bilobate mounds on the sole of fine- to medium-grained quartz sandstones from the estuarine-embayment depositional system of the Upper Devonian Wutong Formation in Wuhan city. The fish feeding trace Osculichnus is closely associated with the highly regular, branched sinuous trace Sinusichnus sinuosus on the bedding plane. Previously, Sinusichnus sinuosus has been typically reported from Late Cretaceous to Miocene marginal-marine sediments, with two records in the Lower and Middle Triassic of South China, and is generally regarded as the burrows of decapod crustaceans. The discovery of Sinusichnus sinuosus in the Upper Devonian, though of relatively small diameter (0.4–4.3 mm) than its Mesozoic and Cenozoic counterparts, extends its stratigraphical distribution and is suggestive of some primitive, small-sized decapod crustacean producers. The Osculichnus makers possibly preyed upon the Sinusichnus makers or other small invertebrates in the sediments. The overall shape and morphological details of the Late Devonian Osculichnus suggest lungfish as candidate trace makers. The fish hunting traces and associated trace fossils from South China thus provide unique insights into the palaeoecology of Late Devonian fishes.

Tentaculitoids have long been recognised as an enigmatic group of marine invertebrates that are widely distributed and highly diversified in the Silurian and Devonian strata. A tentaculitid assemblage is described herein from the Nagaoling Formation spanning the Lochkovian–Pragian boundary in Nanning, South China. Six new species are recognised: Tentaculitesbrevitenui n. sp., Lonchidium cylicus n. sp., Bicingulites nanningensis n. sp., Odessites aurisites n. sp., O. nahongensis n. sp. and Volynites nagaolingensis n. sp. are diagnosed. Two species Podolites sp. and Seretites sp. and one population Uniconus spp. are described in open nomenclature. All above tentaculitid genera can be detected in the Silurian strata from Sweden. The tentaculitids from South China allow transitional skeletal characters between benthic and planktonic tentaculitoids to be described, including conch size, conch wall thickness, septum number and the relationship between external and internal wall sculptures. The fossil assemblage, sedimentary rocks and taphonomic characters indicate that tentaculitids of Nagaoling Formation in South China were deposited in an outer shelf region with weak hydrodynamic condition.

One kind of mysterious underwater circle observed on the seafloor near southern Amami-Oshima Island in subtropical Japan has attracted widespread attention, but its origin has long been unknown. In recent years, based on successive underwater photography, they were shown to represent the patterned structures constructed by male pufferfishes. Here we present a large radial trace fossil from the Upper Devonian Hongguleleng Formation in western Junggar, Xinjiang, northwestern China. They are circular or near-circular patterned structures consisting of numerous radial grooves and ridges. Based on morphological analysis of these specimens and comparison with the modern patterned structures made by pufferfish for courtship, we suggest that this trace fossil may be patterned structure made by male fish in the Devonian to attract females. If true, these structures would be the first reported example of courtship behaviour in the trace fossils of fish, and suggest that animal courtship behaviour has existed for at least 360 million years. These trace fossils provide new material for research on the breeding strategies and sexual selection of Devonian animals, and new insight on the origin and evolution of courtship behaviour.

An exceptionally preserved biota is described from the middle Telychian (Llandovery, Silurian) Fentou Formation of Wuhan, Central China, which preserves nontrilobite arthropods, cnidarians, echinoderms, sponges, fish, and algae as well as abundant shelly fossils and trace fossils in the Skolithos-Cruziana ichnofacies. This biota can be divided into two assemblages on the basis of the biological characteristics, fossil-bearing strata, and their sedimentary environments. Assemblage 1 comprises nonbiomineralized phyllocarids, Sphenothallus, conulariids, complete crinoids and stelleroids, and Burgess Shale–type sponges as well as some uncertain fossils in taxonomy and abundant marine shelly fossils. Assemblage 2 consists of numerous eurypterids, agnathans, chondrichthyes, and a few conulariids, algae, as well as shelly euryhaline fossils. Discoveries of the Fentou biota expand the temporospatial distribution and sedimentary environment of the exceptionally preserved Silurian biota and advances a deepe...

The cephalon of the trilobite Phacopidae was usually separated from the thorax during moulting, and abandoned near the trunk. We statistically evaluated the distribution pattern of the cephala of Omegops cornelius, and found that near 70% of the total cephala were displaced on the right side, from the Upper Devonian deposits of the western Junggar in Northwest China. Omegops cornelius might have actively pushed the cephalon to the right of its body during moulting, indicating their preference to move counterclockwise. This preferred movement direction manifested the behavioural asymmetry in trilobites. A different type of asymmetry has been observed in Phacopidae Plagiolaria nandanensis from the Lower Devonian of Guangxi in South China, where about 67% of the cephala were found on the left side of the trilobite trunks. So the behavioural asymmetry may be diverse (or opposite) in different species of trilobites, and the reasons for the asymmetric moulting and movement patterns of the above two trilobites are likely related to their body structures, or their living environments. These new materials provide evidence for studying the origin and evolution of behavioural asymmetry.

Accurately identifying contourites and analysing the interaction between turbidity flows and bottom currents from the mixed turbidite-contourite systems (MTCSs) in the deep-sea environments are still challenging. Reports on ancient MTCSs are scarce and most of them remain contentious. This study describes at various scales the sedimentological and sedimentary geological characteristics of the Middle Ordovician Yingtaogou Formation, which is identified as a MTCS, from the western margin of the North China Craton (NCC). Twelve typical lithofacies are recognised in the Yingtaogou Formation, which can be grouped into four facies associations interpreted to reflect various deposition from turbidity flow, contour current, debris flow, and hemipelagic settling in the slope–abyssal plain environment. The evidence for contourites is four-fold. Firstly, the palaeocurrent direction based on flute casts on turbidite soles is almost perpendicular to that indicated by traction current structures. Secondly, it is possible to observe a variety of traction current structures (large-scale cross-bedding, cross-lamination, wavy bedding, lenticular bedding, parallel bedding, and horizontal lamination), which are commonly found in reverse and bi-gradational sedimentary sequences at various scales. Thirdly, internal erosive surfaces are widely developed, which reflect the fluid winnowing and velocity fluctuations. Fourthly, these contourites are characterised by an abundance of reverse grading and bi-gradational sequences at various scales. In addition, the contourites identified in this study generally lack bioturbational structures, which is probably related to the late migration and radiation of the Ordovician deep-sea benthos. The sedimentary processes, products, and controlling factors of the interacting down- and along-slope currents were further identified, and a bioturbation-free facies model of contourites and a depositional model of the MTCS were established. This study may contribute to establishing the sedimentological criteria for recognition of ancient contourites and a better understanding of the interaction and spatiotemporal evolution of down- and along-slope sedimentary processes, as well as to a deeper comprehension of the Middle Ordovician palaeoceanographical environment in the western margin of the NCC.

Motor control is an important component of animal movement that relies on the nervous system to conduct coordinated locomotion. Marine trace fossils, recording a myriad of movement patterns of principally invertebrate bilaterians, provide unique geological evidences for the evolution of animal locomotor behaviour. Here we report highly geometrical circular trace fossils from the Upper Ordovician deep-water slope deposits of North China. They consist of a small-sized ring-like main burrow with around 8 or 12 regularly-spaced tangential branches, contributing to semi-octagonal or semi-dodecagonal patterns with an average turning angle between successive branches of about 45° and 30°, respectively. The individual specimens also display regular and locally highly symmetric combination patterns like a Venn diagram. The ordered geometric expression of tiny circular trace fossils here suggests a relatively high level of motor control from minute invertebrate animals. Bilaterian motor control evolution in the early Palaeozoic as evidenced by the marine trace fossil record could be a key ingredient of biological evolutions during the Cambrian and Ordovician radiations. The Ordovician Radiation as an ecological expansion in the marine realm was accompanied by distinct offshore migration of the shallow-shelf ichnofauna and compositional change in the deep-sea ichnofauna. The greatly ameliorated deep-sea food content and relatively homogenous deep-sea food distribution may have promoted more geometrical and patterned trace fossils with a high level of motor control in the deep-sea regime during the Late Ordovician. It is speculated that after the latest Ediacaran–early Cambrian that set up the bilaterian behavioural toolkit, the Ordovician and Cretaceous represent two periods with distinct behavioural and motor control evolution of the deep-sea ichnofauna, which were in pace with revolutions in pelagic organic matter circulation during the corresponding periods.

Abundant Late Devonian radiolarians occur in the siliceous rocks of the Karamay ophiolitic melange in western Junggar. The siliceous rocks are interpreted as deposit in a remnant oceanic basin in view of their petrological and geochemical characteristics. New data suggest that the age of the Karamay ophiolitic melange can be extended from the Ordovician to Late Devonian, thus representing the youngest known oceanic crust in western Junggar, which indicates that the closure of the Paleo-Asian Ocean was at least after the Late Devonian in southern western Junggar. The Carboniferous formation capping the siliceous rocks units comprises, in ascending order, a broad regressive sequence from the abyssal–bathyal turbidites, littoral-neritic carbonates, and calcareous clastic rocks to molasse, indicating that the ocean–continent transformation probably occurred in the Devonian–Carboniferous transition or the early Early Carboniferous. The oceanic basin was filled with volcaniclastic turbidites in the Visean–Serpukhovian, and evolved into a residual sea basin in the Late Carboniferous. The final closure of the Paleo-Asian Ocean in western Junggar was marked by the emergence of molasse in the late Late Carboniferous.

The loboliths, which previously have been called “plurilocular cystoids” in China, are actually the bulbous roots of scyphocrinoids, which occur only, and are widely distributed, in the uppermost Silurian through the lowermost Devonian. Two quite different types of loboliths can be distinguished, the plate- and cirrus-types loboliths, both of which are significant fossils for the correlation of the strata at the Silurian–Devonian boundary. Two lobolith-bearing layers were found in pyroclastic turbidites at the Silurian–Devonian transition in western Junggar, Xinjiang, NW China; all identified loboliths are of the plate type. This discovery provides not only important information for determination of the Silurian–Devonian boundary in western Junggar, but also for the stratigraphic correlation outside of peri-Gongwana and Laurussia. Moreover, the finds are expanding the knowledge of the paleogeographic distribution of scyphocrinoids across facies boundaries between the paleocontinents.