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Mesopsyche Tillyard, 1917 is an extinct genus of Mecoptera belonging to the long-proboscid-bearing Mesopsychidae, an adaptation probably associated with pollination of Mesozoic gymnosperms. Here, we describe two new species, Mesopsyche jinsuoguanensis sp. nov., from the Middle Triassic Tongchuan Formation in Shaanxi Province, and Mesopsyche liaoi sp. nov., from the Upper Triassic Huangshanjie Formation in the Xinjiang Uygur Autonomous Region of China. The new discoveries highlight the diversity of the Mesopsyche in the region during the Mesozoic.

Checklists of all described organisms from the Daohugou biota, and insects from the Haifanggou Formation at Haifeng Village (Beipiao City, Liaoning Province) and the ‘Jiulongshan Formation’ at Zhouyingzi Village (Luanping County, Chengde City, Hebei Province), are provided. Fossil insects from the Daohugou biota are summarized, including a total of 760 valid species reported in 396 research papers from 2001 to April, 2021. The heyday of exploration of Daohugou insects has been lasted for a decade from 2006 to 2016 according to the number of published papers.

Nosodendridae, the wounded-tree beetles, are a small polyphagan family with less than 100 described species placed into two extant and one fossil genera. Here we describe a new nosodendrid genus and species, Mesonosa scandens gen. et sp. nov., from mid-Cretaceous Burmese amber from northern Myanmar (ca. 99 Ma). The new genus differs from extant nosodendrids in its bilobed tarsomeres 2–4, as well as putatively plesiomorphic characters such as strongly protuberant compound eyes and relatively elongate prosternum. The distinctly lobed tarsi are a unique feature within Nosodendridae, and likely represent an adaptation for climbing plants. The discovery of a third wounded-tree beetle genus from the Mesozoic indicates that while their body plan remained relatively conserved since the Cretaceous, nosodendrids have been more ecomorphologically diverse in the geological past than the present day, and thus are an example of a true “living fossil” lineage.

Fleas (Siphonaptera) are medically important blood-feeding insects responsible for spreading pathogens such as plague, murine typhus, and myxomatosis. The peculiar morphology of fleas resulting from their specialised ectoparasitic lifestyle has meant that the phylogenetic position of this diverse and medically important group has remained one of the most persistent problems in insect evolution. Here we test competing hypotheses on the contentious evolutionary relationships of fleas and antliophoran insects using the largest molecular dataset available to date consisting of over 1,400 protein-coding genes, and a smaller mitogenome and Sanger sequence alignment of 16 genes. By removing ambiguously aligned sequence regions and using site-heterogeneous models, we consistently recover fleas nested within scorpionflies (Mecoptera) as sister to the relictual southern hemisphere family Nannochoristidae. Topology tests accounting for compositional heterogeneity strongly favour the proposed topology over previous hypotheses of antliophoran relationships. This clade is diagnosed by shared morphological characters of the head and sperm pump. Fleas may no longer be regarded as a separate insect order and we propose that Siphonaptera should be treated as an infraorder within Mecoptera, reducing the number of extant holometabolan insect orders to ten.

Stegocoleus Jarzembowski & Wang is an enigmatic genus in the family Ommatidae, known to date only from Burmese amber. This genus possesses a unique combination of characters, including antennal grooves on the ventral side of head, well-developed epipleural rims, and presence of separated procoxae, which makes its systematic position unclear. Here we report two new species of Lepidomma from mid-Cretaceous Burmese amber, L. longisquama sp. nov. and L. jarzembowskii sp. nov. Based on these well-preserved specimens and new morphological details revealed by widefield fluorescence and confocal microscopy, we discuss the morphological similarities between Lepidomma and the enigmatic Stegocoleus. We suggest that Stegocoleus is not a basal ommatid, but a highly derived form of ommatid beetles.

Clam shrimp (Spinicaudata) are worldwide distributed branchiopod crustaceans specialised in ephemeral freshwater habitats. The Carboniferous is an important period for the early evolution and diversification of clam shrimp. Compared with the rare and geographically confined fossil record of the Devonian, clam shrimp in the Carboniferous have a much wider geographical distribution and higher biodiversity. Over 20 genera of clam shrimp have been recorded in the Carboniferous all over the world, but they are sparse in China. To date, five records of Carboniferous clam shrimp have been reported from China (Pruvost, 1927; Zhang et al., 1976; Wang, 1987; Zheng et al., 1988; Liu & Fan, 1995; Liao et al., 2019). Among them, four species Lioestheria? mathieui Pruvost, 1927, Protomonocarina huixianensis Wang, 1987, Retrofractus lingyuanensis Liu & Fan, 1995, and Pemphilimnadiopsis cheni Liao, Shen & Huang, 2019, are found in the Pennsylvanian Benxi Formation in North China (Pruvost, 1927; Zhang et al., 1976; Wang, 1987; Liu & Fan, 1995; Liao et al., 2019).

Mesopanorpodidae Tillyard, 1918 is a small extinct family of Mecoptera described from France, Russia, China, Australia, and South Africa ranging from the Late Permian to the Late Triassic. The systematic placement of Mesopanorpodidae is debated; some suggested it as a separate family (Riek, 1953, 1976; Carpenter, 1992; Ren et al., 1995; Van Dijk & Geertsema, 1999; Hong et al., 2002; Hong & Guo, 2003; Sun et al., 2007), whereas others considered it a member of Permochoristidae Tillyard, 1918 (Martynova, 1962; Novokshonov, 2001; Novokshonov et al., 2004; Bashkuev, 2011). As all mesopanorpodids distinctly differ from Permochoristidae by their constant four-branched Rs and M in both forewing and hind wing, here we regard it as a valid family. Herein, we describe the first species of Prochoristella Riek, 1953 (Mesopanorpodidae) from the Xiaofengmidingzi Formation of Jilin Province, northeastern China.

Thanerocleridae is a small family of predaceous cleroid beetles with a cosmopolitan distribution. Here we describe a new genus and species, Mesozenodosus insularis gen. et sp. nov., from early Cenomanian Charentese amber from the Fouras deposit, Charente-Maritime department in south-western France. The new genus belongs to the relictual subfamily Zenodosinae represented in the Recent fauna by a single Nearctic species, Zenodosus sanguineus (Say). Mesozenodosus gen. nov. can be differentiated from Zenodosus and the two fossil zenodosine genera from the approximately contemporaneous Burmese amber by its smaller body size, more elongate body, non-carinate pronotal margins, and apical antennomere with an oval depression. The new fossil confirms a wider diversity and distribution range of Zenodosinae in the mid-Cretaceous than in the present day and provides further evidence of the relictual status of the subfamily.

Eucnemidae is a relatively large beetle family belonging to the polyphagan superfamily Elateroidea. Numerous fossil eucnemids have been reported from Cenozoic deposits, but the Mesozoic record of Eucnemidae is much sparser. Here we describe and figure a new eucnemid beetle, Muonabuntor grandinotalis gen. et sp. nov., discovered from mid-Cretaceous Burmese amber (ca. 99 Ma). The new genus resembles extant Jenibuntor and Euryptychus in having simple hypomera and tubular antennomeres 9–11, but differs from the latter genera by its comparatively longer pronotum, weakly striate elytra, and large metacoxal plates. The fossil record and classification system of Eucnemidae are also reviewed.

Elucidating the phylogenetic affinities of enigmatic fossils is crucial for resolving the early diversification of the superfamily Cucujoidea, a diverse group of polyphagan beetles whose relationships remain contentious. The systematic position of the Cretaceous genus Pleuroceratos known from Burmese amber has been uncertain; the genus was previously placed into Silvanidae, Sphindidae, and Cucujoidea incertae sedis. Here we describe a new species, Pleuroceratos jiewenae sp. nov., from mid-Cretaceous Burmese amber and conduct a formal phylogenetic analysis to elucidate the position of the genus. We recover Pleuroceratos as nested within the family Phloeostichidae, represented in the modern fauna by four genera of fungivorous subcortical beetles with a highly disjunct distribution range. Pleuroceratos beetles are the sole fossil members of Phloeostichidae known to date and indicate that the family begun to diversify by the mid-Cretaceous.

Professor Qi-Bin Lin (Figs 1, 2) was born on February 15th, 1935 (same birthday as the first author, Di-Ying Huang) in Putian, Fujian Province, southeastern China. He graduated from the Department of Biology of Nanjing University in 1959 and has been working at the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences (NIGPAS) since then. In his early career, he did research on Permian brachiopods with Prof. Yu Wang. Although there were sporadic studies on insect fossils in China before China’s Liberation, palaeoentomology was still a blank in China at that time and there was a lack of professional researchers. That was the reason why the institute’s leader assigned him to research on insect fossils. Lin went to the Beijing Institute of Entomology, Chinese Academy of Sciences (later merged into the Institute of Zoology, Chinese Academy of Sciences) in 1961 to study entomology for one year. He studied under the supervision of the famous entomologist, Prof. Juan-Jie Tan, who was not only an excellent coleopterist, but also one of the pioneers in palaeoentomology of China.

Ambers in China have been described from the various localities of both Cretaceous (e.g., Xixia amber from Henan Province and Jalainur [Zhalainuoer] amber from northeastern Inner Mongolia) and Palaeogene (e.g., Eocene Fushun amber of Liaoning Province and Miocene Zhangpu amber of Fujian Province) ages to date (e.g., Hong, 1981, 2002; Shi et al., 2014; Wang et al., 2014; Azar et al., 2019; Wang et al., 2021). Here we report a new amber locality from the Late Oligocene of Nanning Basin, Guangxi, southern China. The first amber piece was collected by one of the authors (GCZ) on 5 June 2008. In a recent field work in early 2021, we further discovered more than 50 smaller amber pieces, which are reported here.

The archostematan family Ommatidae Sharp & Muir, 1912 represent one of the oldest beetle lineages, originating probably in the Permian or early Triassic (Tan et al., 2012; Cai & Huang, 2017; Zhang et al., 2018). Fossil ommatids have been known since the Triassic and, along with other members of the suborder Archostemata, are reminiscent of the earliest and most basal Permian beetles, with which they share a dorsoventrally compressed body, distinctly raised elytral veins, and characteristic rows of window punctures on the elytra (Crowson, 1962). As such, archaic ommatid beetles have sometimes been referred to as ‘living fossils’ (Jarzembowski et al., 2018). Only six extant ommatid species with a highly disjunct distribution are known (Hörnschemeyer & Beutel, 2016), but the family was much more diverse in the Mesozoic.

Mesozoic insect fossils are abundant in Xinjiang, northwestern China, mainly from the Triassic and Jurassic strata. The first Xinjiang insect fossils found were from the Meiyaogou section, north of Turpan City (Ping, 1935). Ping (1935) did not provide a detailed introduction to the specific stratum due to a limited stratigraphic survey of this area at that time, but it was considered to belong to the Upper Jurassic. The Upper Jurassic strata in the Meiyaogou section were represented mainly by the Sanjianfang Formation, which is characterized by gray-yellow-green sandstone-siltstones with purple-red sandstone strips. However, whether these fossils reported by Ping (1935) were from the Sanjianfang Formation is still uncertain. These insect fossils are known from just two orders: Dermaptera and Plecoptera. The mayfly species Ephemeropsis tingi (Demoulin, 1954; Edmunds, 1972; Kluge, 2004) was thought to be significantly different from Ephemeropsis trisetalis from the Jehol biota. Another species, Sinoephemera kingi, is more similar to a stonefly nymph. Mesonetopsis zeni, a taxon thought to be relate to the common component of the Late Jurassic in Central Asia (Mesoneta), is in fact an odonatan nymph (Demoulin, 1954).

Brachypsectridae is a species-poor elateroid family containing two extant genera with a disjunct distribution range spanning the Nearctic, Palaearctic, Oriental, and Australian regions. Here we describe a second Texas beetle from mid-Cretaceous Burmese amber, Hongipsectra electrella gen. et sp. nov. The new genus can be distinguished from all hitherto known brachypsectrids by the 11-segmented sexually dimorphic antennae with antennomeres 6–10 bilamellate in males and serrate in females, pronotum with a pair of posterolateral carinae and an M-shaped notch in the posterior margin for the reception of a cordiform scutellum. The present discovery adds a fourth genus and eleventh species to Brachypsectridae. Given that two of the known Texas beetle genera are from the Cretaceous Burmese amber, the family probably have been much more widespread and diverse in the Mesozoic than it is today. A key to the extant and fossil genera of Brachypsectridae is provided, along with a list of fossil species.

Professor You-Chong Hong, a famous Chinese palaeoentomologist, was born in Nan’ao County, Shantou City, Guangdong Province on 5 November 1929 and passed away in Beijing on 4 July 2019. In 1953, Prof. Hong graduated from the Beijing College of Geology (China University of Geosciences, Beijing) and was assigned to the Laboratory of Ferrous Metal of the Department of Geology and Minerals of the Ministry of Geology. From 1957 to 1958, he worked in the Department of Stratigraphy and Palaeontology, Institute of Geology and Mineral Resources, Chinese Academy of Geological Sciences. He studied fossil mollusks and later fossil insects in the Soviet Academy of Sciences from 1958 to 1960 (Fig. 1). He returned to the Chinese Academy of Geological Sciences from 1960 to 1963; worked at the Tianjin Institute of Geology and Mineral Resources, Ministry of Geology and Minerals from 1963 to 1984; and worked at the Beijing Museum of Natural History after 1984.

The amber is a fossilized vegetal resin ranging from a few millions to more than 300 million years (mid-Carboniferous) in age (Sargent Bray & Anderson, 2009). It constitutes a superb material for the conservation of biological inclusions in their minute three-dimensional details (Poinar, 2003).

With over 4,600 species distributed worldwide, the net-winged beetles belong among the most speciose elateroid lineages. Despite this, beetles of the family Lycidae are rare in the fossil record. A new genus and species of Lycidae, Cretolycus praecursor gen. et sp. nov., is herein described based on a single specimen preserved in mid-Cretaceous Burmese amber. Cretolycus praecursor represents the second known lycid from the Mesozoic. A new tribe, Cretolycini trib. nov., is erected for the species, characterised by 11-segmented filiform antennae, 3-segmented labial palpi with an enlarged apical palpomere, and elytra without costae. A catalogue of fossil net-winged beetles is appended.

Silvanidae is a small group of cucujoid beetles, and their fossil record is poorly documented. The two recently described genera from Burmese amber, Cretoliota Liu et al. and Protoliota Liu et al. , are distinctive among all known Silvanidae, displaying markedly long antennae and mandibular horns in males, as found in the extant Uleiota Latreille. Due to the limited sampling of fossil specimens, the morphological variations of male mandibular horns remain a mystery. Here we report six well-preserved specimens of Protoliota with both male and female genitalia exposed from mid-Cretaceous Burmese amber. Our discovery confirms the presence of remarkable sexual dimorphism in Protoliota . Males of Protoliota antennatus Liu et al. display short to very long mandibular horns and much longer antennae. Interesting morphological convergence of the beetles (Silvanidae and Staphylinidae) living under the bark of dead trees is briefly discussed. Our discovery represents the first definitive sexual dimorphism in beetles from Burmese amber.

Triassic insect fossils from China are very limited. Here we report on numerous insect fossils discovered in the Upper Triassic Laohugou Formation at Heishanyao, Qinhuangdao, Hebei Province. These fossils are represented mainly by forewings of cockroaches and coleopteran elytra. The insect assemblage is most similar to that from the Upper Triassic Momonoki Formation of Japan. Fossils of the Laohugou Formation have been poorly known, so our discovery of new fossil insects bear significance for understanding the biota and sedimentary environment of this formation. The Mesozoic stratigraphic division in the Liujiang Basin has been controversial, and the usage of stratigraphic units has been inconsistent. Here we refine the stratigraphic sequence, from the bottom to the top, of the Upper Triassic Laohugou Formation, the Lower-Middle Jurassic Yaopo Formation, the Upper-Middle Jurassic Longmen Formation, the Upper Jurassic Tiaojishan Formation, and the Lower Cretaceous Zhangjiakou Formation. The Laohugou Formation is scattered in various basins in western Liaoning and northern Hebei, with the lower part mostly characterized by thick layers of complex conglomerates, suggesting a regional tectonic uplift. There is a sedimentary discontinuity between the Laohugou Formation and the Yaopo/Beipiao Formation, reflecting the uplifting activities during the late Late Triassic-early Early Jurassic in eastern China. The Laohugou Formation is overlaying on various ancient strata, representing the first regional unconformity of the northeastern margin of the North China Craton.

Confocal laser scanning microscopy is an essential analytical tool in biological, biomedical, and material sciences, integrating microscope manufacturing technology, optical-electronic technology, and computer technology. In the last decade, confocal laser scanning microscopy has been successfully applied to the study of amber bioinclusions. Enhanced signal to noise ratios, resolution power, capability of optical sectioning, three-dimensional reconstruction, and better performance when imaging thicker samples provide a great deal of valuable and detailed morphological information about amber fossils. We briefly discuss the practical applications of CLSM in amber studies and compare it with other imaging methods commonly used in the field, including bright-field microscopy, wide-field fluorescence microscopy, and micro-computed tomography. A general procedure for imaging amber inclusions with CLSM is provided, with a focus on pretreatments and image processing.

Siphonophora hui Jiang et al., 2019, known from the mid-Cretaceous Burmese amber, is the first formally described fossil species of the extant myriapod family Siphonophoridae. Here we re-study this species using confocal laser scanning microscopy (CLSM) on the basis of three new specimens from the same deposit. A comparison between the fossil and extant species of Siphonophora is given and several new morphological details are discussed.

Cormopsocus neli Hakim, Azar & Huang sp. nov., a new cormopsocid species from the mid-Cretaceous Burmese amber is characterized, described, and illustrated. Its taxonomic position is discussed. This is the second species of the Cormopsocidae, the most recently discovered trogiomorphan family in the Burmese amber.

A new species of the extinct scydmaenine genus Euroleptochromus Jałoszyński (Mastigitae: Leptochromini), E. tuberculatus Yin & Cai, sp. nov., is described from Eocene Baltic amber. It can be separated from the two previously known congeners by the different proportions of the body parts and spination of the profemur, and more importantly, lack of an elongate postgenal process of the head. Our finding demonstrates for the first time a notable variability of the postgenal structures within Euroleptochromus.

The Shanwang Fauna has been one of the well-known Miocene Konservat-Lagerstätten for a long time, but the high-fidelity preservation of the fossils has been often ignored. This paper illustrates the exceptional preservation displayed by some fossil insects from the Shanwang Formation. The microstructures of the preserved exoskeletons were analyzed using a scanning electron microscope and a transmission electron microscope. The epicuticle, procuticle, and some fine details such as cuticular scales could be recognized from the structural remains. These details could enable the identification of valued taxonomic and phylogenetic features and contribute to understanding the diagenetic environment.

The Yanliao entomofauna, first established by Hong in 1983, refers to a Middle Jurassic insect assemblage widely distributed in northern China. The fossil insects are primarily preserved in the Haifanggou Formation and its correlated strata. In the beginning of this century, the Yanliao entomofauna was revived thanks to the discovery of abundant exceptionally preserved fossils, especially a huge number of insects, in the Daohugou area. Then, the Yanliao biota became well-known, and subsequently enlarged with more fossils collected from the interbeds of the overlying Tiaojishan Formation. Recently, the Yanliao biota has been divided into an early assemblage, represented by the Daohugou beds (Middle Jurassic to earliest Late Jurassic), and a late assemblage, represented by the Linglongta beds (early to middle Late Jurassic). The early insect assemblage, i.e. fossil insects from Daohugou, contains at least 24 insect orders, representing one of the most diverse entomofaunas in geological history. The age difference between core fossil layers of the Daohugou assemblage and the Linglongta assemblage is less than 5 Ma, but no same animal species from both have been discovered to date, because of violent tectonic movements and fierce volcanic eruptions. The representative insect from the early assemblage is Yanliaocorixa chinensis, which is distinctly different from the dominated corixids from the late assemblage. Insects of Yanliao entomofauna generally resemble those from the Shar Teg biota from Mongolia and the Karatau biota from Kazakhstan. The Yanliao biota rapidly declined in middle of the Late Jurassic (ca. 155 Ma) with the advent of arid climate, whereas some of the relict groups migrated southwards. Until the mid-Cretaceous, represented by the Burmese amber, a number of endemic insect groups of Daohugou are still recorded, but they have never been found in the Jehol biota, representing relicts of the Yanliao entomofauna.

Burmese amber represents the world’s most diverse biota in the Mesozoic. Previous studies have focused on the biodiversity of its inclusions, as well as pholadid borings. Here we report a variety of marine animals symbiotic with or adhere to Burmese amber or the amber deposits, including crinoid columns, corals and oysters. We propose that there is no distinct evidence indicating the secondary transportation of Burmese amber over long distances. The ancient sedimentary environment was likely located in the coastal area. The hardening time of the resin was not long after secretion. The resin has been mixed with fragments of marine organisms in the ancient sediments, and has been deposited for a long time. The zircon age in the sediments surrounding amber approximately represents the age of Burmese amber, but due to limits of the method, the current zircon U-Pb SIMS age may be younger. Therefore, as far as the situation is concerned, the age of Burmese amber may be close to the boundary between the Albian and Cenomanian, or even late Albian. We suggest that it is plausible to generally refer to the age of Burmese amber as mid-Cretaceous, and a precise age requires further biostratigraphic and chronological studies.