Lower Cretaceous Yixian Formation Research Articles

Lacustrine varves in the Lower Cretaceous Yixian Formation of western Liaoning, Northeast China: Implications for seasonal to sub-decadal palaeoclimate variability associated with the Jehol Biota and “Dinosaur Pompeii”

The Lower Cretaceous Yixian Formation in western Liaoning, China contains the exceptionally well-preserved Jehol Biota, and includes the famous assemblages known as “Dinosaur Pompeii”. In this study, we focus on the fossil-rich Zhuanchengzi Bed near Yingwoshan, and describe laminated lacustrine successions that show prominent rhythmites to understand subdecadal palaeoclimate variability. We highlight the cyclicity preserved at a millimetre-scale based on analysis of the rhythmic alterations between the light- and dark-coloured carbonate-siliciclastic layers. Coupling petrographic with phase-specific geochemical analyses, we infer these laminated successions represent varves. The light-coloured layers of the couplets, containing dolomite-dominated carbonates, developed during warm seasons as a result of chemical precipitation enhanced by photosynthetic activities and rhythmic changes in the ambient water properties. The dark-coloured layers are mostly composed of siliciclastic and clay minerals representing terrestrial input during cold seasons. Varve thickness variations likely record seasonal climate changes regulated by ancient Asian Monsoons and decade-level cyclicities, such as ENSO-like and solar cycles. Overall, the varve records in the Yixian Formation offer a novel perspective on the palaeoseasonality of the Jehol Biota and provide insights into the dominant climate mode over interannual time scales of the Early Cretaceous greenhouse world.

Early‐diverging Titanosauriform (Dinosauria, Sauropoda) Teeth from the Lower Cretaceous Yixian Formation of Southeastern Inner Mongolia, Northeast China

AbstractThree eusauropod teeth (SDUST‐V1064, PMOL‐AD00176, PMOL‐ADt0005) are reported from the Lower Cretaceous Yixian Formation of Ningcheng, southeastern Inner Mongolia, China. Two of them (SDUST‐V1064, PMOL‐AD00176) are assigned to early‐diverging titanosauriforms in having slightly mesiodistal expansion at the base of the tooth crown, a slenderness index value >2.0 and <4.0, and D‐shaped cross section. Furthermore, SDUST‐V1064 and PMOL‐AD00176 are referred as an Euhelopus‐like titanosauriform on the basis of having a sub‐circular boss on the lingual surface and an asymmetrical crown‐root margin which slants apically, respectively. CT scan data of SDUST‐V1064 reveals new dental information of early‐diverging titanosauriforms, for example, the enamel on the labial side thicker than that on the lingual side, an enamel/dentine ratio of 0.26 and a boss present on the lingual side of the dentine of the crown.

New fossil caddisflies (Trichoptera, Dysoneuridae) from the Lower Cretaceous of Inner Mongolia, China

A new caddisfly species, Khasurtia apertalocularis sp. nov., and a Dysoneuridae gen. indet. sp., are described and illustrated, and Utania defecta Sukatsheva, 1982 is redescribed, based on 13 fossil specimens from the Lower Cretaceous Yixian Formation of Inner Mongolia, China. This is the first report of the family Dysoneuridae in China, enhancing the geographical distribution of this family and providing reference to the paleogeography. New specimens show that the species previously classified as Dysoneuridae from the compression fossils and Myanmar amber belong to different families based on the characters of wing, ocelli and antennae; and support that the caddisflies in Myanmar amber be elevated to two families, Burmapsychidae and Cretapsychidae.

Two new species of Ghilarellinae (Hymenoptera, Cephoidea, Sepulcidae) from the Lower Cretaceous

One new species, Ghilarella elegantula sp. nov., in the family Sepulcidae is described and illustrated based on a well-preserved compression fossil specimen from the Lower Cretaceous Yixian Formation of northeastern China. The new species is characterized by having a large body size; forewing with costal area obviously narrowed basally, Sc and 2r-m absent, 1-Rs short, cell 1mcu large; and ovipositor elongated. In addition, Ghilarella cf. mercurialis is given its own name Ghilarella kopylovi as the new species in Ghilarella. An updated key for the known species of Ghilarella is provided. Moreover, a well-preserved ovipositor is reported for the first time in the subfamily Ghilarellinae. The two new species not only improve our understanding of Ghilarella by adding more morphological features, but also expand the distribution ranges of Ghilarellinae fossil records.

An extraordinary fossil captures the struggle for existence during the Mesozoic

Dinosaurs and mammals have coexisted for the last ~ 230 million years. Both groups arose during the Late Triassic and diversified throughout the Mesozoic and into the Cenozoic (the latter in the form of birds). Although they undoubtedly interacted in many ways, direct fossil evidence for their interaction is rare. Here we report a new fossil find from the Lujiatun Member of the Lower Cretaceous Yixian Formation of China, showing a gobiconodontid mammal and psittacosaurid dinosaur locked in mortal combat. We entertain various hypothesized explanations for this association, but the balance of the evidence suggests that it represents a predation attempt on the part of the smaller mammal, suddenly interrupted by, and preserved within, a lahar-type volcanic debris flow. Mesozoic mammals are usually depicted as having lived in the shadows of their larger dinosaurian contemporaries, but this new fossil convincingly demonstrates that mammals could pose a threat even to near fully-grown dinosaurs. The Yixian Formation—and the Chinese fossil Jehol Biota more broadly—have played a particularly important role in revealing the diversity of small-bodied dinosaurs and other fauna. We anticipate that the volcanically derived obrution deposits specific to the Lujiatun Member will likewise continue to yield evidence for biotic interactions otherwise unknown from the rest of the fossil record.

Arlenea delicata gen. et sp. nov., a new ephedroid plant from the Early Cretaceous Crato Formation, Araripe Basin, Northeast Brazil

Ephedroid macrofossils have been widely documented in Cretaceous deposits, including numerous from the Lower Cretaceous Yixian Formation of NE China. However, few ephedroid macrofossils have been reported from South America. Herein, we describe a new plant of the family Ephedraceae, Arlenea delicata gen. et sp. nov., from the Lower Cretaceous Crato Formation of the Araripe Basin, Northeast Brazil, based on the vegetative and reproductive structures. It has the typical morphological characteristics of ephedroid plants, including fertile reproductive branches, opposite phyllotaxy, terminal female cones, a sympodial branching system, longitudinally striated internodes, and swollen nodes. Our new finding is unusual in having inner chlamydosperms subtended by two pairs of bracts, reproductive units connected to branches through swollen receptacles and a smooth seed surface. This new ephedroid taxon from the Crato Formation increases our understanding of plant diversity of this group during the Early Cretaceous. Furthermore, the general morphology (fleshy bracts and enlarged receptacles) of this new fossil discovery indicates that seeds of this plant may have been dispersed by animals such as pterosaurs (mainly the Tapejaridae) and birds (Enantiornithes and Ornituromorpha). If true, this would explain the cosmopolitan distribution of Ephedraceae in the Lower Cretaceous.

A new pterosaur specimen from the Lower Cretaceous Yixian Formation of Liaoning Province, China: The oldest fossil record of Nurhachius

ABSTRACT The Istiodactylidae is one of three ornithocheiroid pterosaur lineages, characterised by a large nasoantorbital fenestrae and labiolingually compressed teeth. Their remains have been reported from Early Cretaceous rocks of northeastern China and Western Europe. A new istiodactylid pterosaur from the upper part of the Yixian Formation (Jingangshan Member) of the Jehol Group, distributed in western Liaoning Province and neighbouring areas, is described on the basis of an incomplete specimen including the partial skull, forelimb and hindlimb bones, and pelvis. This individual, here designated as a referred specimen of Nurhachius (Nurhachius sp.) is a skeletally almost mature pterosaur with an estimated wingspan of 1.6 m. This specimen is not only the geologically oldest known occurrence of Nurhachius, but also a new component of the pterosaur assemblage of the Jingangshan Member, and provides new information on the pelvis and hindlimb of istiodactylids and the palaeobiology of this clade. Considering previous reports of the istiodactylid remains and the geological ages of the strata that yielded them, it is suggested that different istiodactylids existed in Europe and China during the late Barremian.

Discovery of Sinaeschnidia heishankowense (Odonata: Aeschnidiidae) from the Lower Cretaceous of Baiwan Basin, southwestern Henan, China: Biogeographic implications

The Jehol Biota is the best-preserved Cretaceous terrestrial biota and one of the most important treasures housing exceptionally-preserved fossils in the world. The Jehol Biota sensus stricto is found distributed in northern Hebei, western Liaoning and southeastern Inner Mongolia, northeast China, while the Jehol Biota sensu lato is distributed in most of East Asia. The three-stage evolution of the Jehol Biota suggests that the biota extended south to the Qinling-Dabie mountains at its second stage, including western and southern Henan. Here the adult dragonfly Sinaeschnidia heishankowense Hong, 1965 is reported for the first time from the Baiwan Formation of the Baiwan Basin, Zhenping County, southwestern Henan, China. S. heishankowense is one of the representatives of the second stage of the Jehol Biota, previously only recorded in the Lower Cretaceous Yixian Formation in western Liaoning and southeastern Inner Mongolia, and the equivalent strata in China. This finding confirms that the Jehol Biota reached southwestern Henan at its second stage, and that the Baiwan Formation in the Baiwan Basin could be generally correlated with the Yixian Formation in western Liaoning, assigned to a middle Barremian age (Lower Cretaceous) rather than to the Upper Jurassic as previously considered.

The first discovery of Mesoraphidia amoena (Raphidioptera: Raphidiomorpha: Mesoraphidiidae) from the Lower Cretaceous Laiyang Formation of China

A new snakefly specimen, identified as Mesoraphidia amoena (Raphidioptera: Raphidiomorpha: Mesoraphidiidae), is discovered from the Lower Cretaceous Laiyang Formation of Shandong Province, China. M. amoena was previously only known from the Lower Cretaceous Yixian Formation in western Liaoning Province, China. The discovery of M. amoena from Laiyang Formation further confirms the close relationship between these two formations. The fossil record of Mesoraphidia and its palaeogeographic distribution are also summarized.

A Cretaceous Chafer Beetle (Coleoptera: Scarabaeidae) with Exaggerated Hind Legs-Insight from Comparative Functional Morphology into a Possible Spring Movement.

The phenomenon of exaggerated morphological structures has fascinated people for centuries. Beetles of the family Scarabaeidae show many very diverse exaggerated characters, for example, a variety of horns, enlarged mandibles or elongated antennal lamellae. Here, we report a new Mesozoic scarab, Antiqusolidus maculatus gen. et sp. n. from the Lower Cretaceous Yixian Formation (~125 Ma), which has unusually robust and structured hind legs with greatly enlarged spurs and a unique elongated apical process. Based on simulations and finite element analyses, the function of these structures is hypothesized to support springing to aid movement and fighting. Based on available morphological characters, we performed phylogenetic analyses (maximum parsimony) of the main subfamilies and families of Scarabaeoidea. The results support the placement of Antiqusolidus gen. n. as a sister group of Rutelinae within the phytophagous lineage of pleurostict Scarabaeidae. Furthermore, the unusual delicate color marking patterns in the fossil specimens suggest that the new species might have been diurnal and potentially visited the leaves or flowers of Early Cretaceous plants. This morphological and functional study on this extinct scarab species provides new sights into exaggerated structures in Mesozoic insects.

A new titanosauriform sauropod with an unusual tail from the Lower Cretaceous of northeastern China

A new titanosauriform sauropod, Ruixinia zhangi gen. et sp. nov., is described. It was recovered from the Lower Cretaceous Yixian Formation of Liaoning Province, northeastern China. Ruixinia is characterized by a unique combination of characters, including the following autapomorphies: distinct foramina present at the anterodorsal corner of the pleurocoels of the mid-posterior dorsals; anterior caudal neural spines bifid; anterior caudal neural spines with projecting subtriangular processes on the anterior margins of the neural spines; distinct grooves present on the lateral surface of neural arches in Caudals 2-12, just dorsal to the base of the caudal ribs; a transition point present between Caudal 22 and Caudal 23 with Caudals 1-22 much larger than more posterior caudals in size; distalmost six caudals fused; Chevron 18 with a bifurcated posterior process; Chevron 20 approximately pentagonal in lateral view; Chevrons 23-36 plank-shaped and unfused distally; lateral bulge developed on the lateral surface of the posterior lobe of the ilium; posterior margin of the tibial shaft strongly convex. Phylogenetic analysis places Ruixinia within the Titanosauriformes. The new find increases the diversity of early-branching Titanosauriformes in China and highlights the tail morphological diversity within this clade.

A new tarsophlebiid dragonfly from the Lower Cretaceous of western Liaoning, NE China (Insecta: Odonatoptera, Panodonata)

A well-preserved dragonfly Turanophlebia liaoningensis sp. nov., belonging to the family Tarsophlebiidae, is described from the Lower Cretaceous Yixian Formation in the Huangbanjigou Village, western Liaoning, China. This is the second species of Turanophlebia recovered in China, although it was widely distributed in Eurasia during the Late Jurassic and Early Cretaceous. Turanophlebia liaoningensis sp. nov. differs from all other species of Turanophlebia in the hindwing pterostigma covering 6–8 cells and cubito-anal area with five rows of cells between CuA and the posterior wing margin. The discovery provides new insight into the biodiversity and evolution of Tarsophlebiidae.

New Pamphiliids with Varying Venations from Lower Cretaceous Yixian Formation of Northeast China (Hymenoptera, Pamphiliidae)

Simple SummaryThe presence of various morphologies of the ap-Cu, an extra vein with different lengths in the forewing, is a special character in Pamphiliidae. In Juralydinae, this vein is usually absent or extremely short. Here, we describe one new genus and three new species of Juralydinae with varying lengths of the ap-Cu from the Lower Cretaceous Yixian Formation in Duolun County, Inner Mongolia, China, and revise the diagnostic characteristics of Juralydinae. The new specimens expand the diversity of Pamphiliidae in the Mesozoic and strengthen our knowledge of venation variation.One new genus and three new species of Pamphiliidae, Dolicholyda obtusata gen. et sp. nov., Dolicholyda confluens sp. nov., and Dolicholyda angusta sp. nov. are described and illustrated. All of them were collected from the Lower Cretaceous Yixian Formation in Duolun County, Inner Mongolia, China. The new genus is established based on the following characters: body surface without punctations; forewing with pterostigma lanceolate and sclerotized around the margins; angle between 1-M and 1-Cu nearly 90°; cell 1mcu long and obviously longer than length of pterostigma. In most cases, the ap-Cu is present, and its length varied. Additionally, we revise the diagnostic characteristics of Juralydinae based on the new specimens. New findings enhance our understanding of the wing venation characteristics of fossil pamphiliids and expand the diversity of Pamphiliidae in the Mesozoic.

New species of Probaisselcana (Orthopera, Elcanidae) from the Lower Cretaceous Yixian Formation of China (Jehol Biota) and the mid-Cretaceous amber of northern Myanmar amber

Two new extinct species of Probaisselcana (Orthoptera, Elcanidae) are described: P. minuta sp. nov. based on three compression fossils from the Lower Cretaceous Yixian Formation of China and P. zhengi sp. nov. based on a male and a female in mid-Cretaceous amber of northern Myanmar. The distally dichotomous R, equal length of CuPa and free CuPaα, ovipositor more than twice the length of pronotum, hind tibiae with three pairs of small and leaf-like spurs of P. minuta sp. nov. can differ it from all other Probaisselcana species. P. zhengi has a CuPa longer than free CuPaα, narrow anal area with mostly simple crossveins, relatively short ovipositor and extremely strong scapus, which can differ from other species of the genus. The Myanmar specimens extend the genus to the mid-Cretaceous.

The second species of Rudiaeschna (Odonata, Rudiaeschnidae) discovered in the Lower Cretaceous of Inner Mongolia, Northeast China

Rudiaeschna jarzembowskii sp. nov., the second species of the small aeshnopteran family Rudiaeschnidae, is described from the Lower Cretaceous Yixian Formation at the Liutiaogou locality, Ningcheng County, Inner Mongolia, NE China. The new species differs from the type species of the family, namely Rudiaeschna limnobia, in possessing less cells and crossveins in nearly all parts of forewing. It also shows a distally forked vein RP2, a character that was previously only known in taxa of the much more recent and derived aeshnopteran family Aeshnidae.

New fossil Xyelidae (Insecta, Hymenoptera) from the Lower Cretaceous Yixian Formation of northeast China

Three new species, Brachyoxyela conjunctiva sp. nov., Brachyoxyela leei sp. nov. and Brachyoxyela elliptica sp. nov., in the tribe Macroxyelini, subfamily Macroxyelinae of the family Xyelidae, are described and illustrated. All type specimens were collected from the Lower Cretaceous (Barremian–Aptian) Yixian Formation. Brachyoxyela conjunctiva sp. nov. and Brachyoxyela leei sp. nov. were from Huangbanjigou, Beipiao City, Liaoning Province, China, and Brachyoxyela elliptica sp. nov. from Sandaogou, Duolun County, Inner Mongolia, China. These specimens are assigned to a previously erected genus Brachyoxyela Gao, Zhao and Ren, 2011 based on the characters: vein Sc joining R distad origin of Rs and antenna with thread (terminal part of flagellum distal to the enlarged first flagellomere) longer than the first flagellomere. A key to species of Brachyoxyela is provided.

Litholamprima qizhihaoi sp. nov., a new stag beetle (Coleoptera: Lucanidae) from the Lower Cretaceous Yixian Formation, China

A new fossil stag beetle (Lucanidae), Litholamprima qizhihaoi sp. nov., is described and figured from two well-preserved specimens from the Lower Cretaceous Yixian Formation in western Liaoning, China (125 Ma). Aditionally, new material of female specimens of the genus Litholamprima Nikolajev & Ren, 2015 provide further evidence for the taxonomic position of other fossil stag beetles that share a similar habitus with species of Litholamprima. The new discovery enriches our knowledge of the biodiversity and early evolutionary history of stag beetles during the Cretaceous.

Two New Fossil Sawflies of Pamphiliidae (Hymenoptera: Symphyta) from the Mesozoic of Northeastern China

Simple SummaryTwo new species and one new specimen of Scabolyda (Pamphiliidae) are described from the Mesozoic of northeastern China. Structures of antennae, genitalia, and legs, especially the hind tarsal claw, are preserved. The documentation of these new structures helps to link extant and fossil taxa of Pamphiliidae.Two new species of Pamphiliidae, Scabolyda latusa sp. nov. and Scabolyda tenuis sp. nov. are described and illustrated from the late Middle Jurassic Jiulongshan Formation and the Lower Cretaceous Yixian Formation of northeastern China, respectively. A new specimen of Scabolyda orientalis Wang, Rasnitsyn, Shih and Ren, 2014 with distinct male genitalia is documented for the first time. Based on the specimens with new and distinct structures of legs, antennae, and genitalia, the morphological characters of Scabolyda are supplemented: antenna with ca. 13–14 flagellomeres; fore leg with tibia without pre-apical spur; hind leg nearly 0.6 times as long as the body, hind tarsal claw without setae and its inner tooth not developed. In addition, the tarsal claw characteristics found in the new species may suggest Scabolyda has a closer relationship with Cephalciinae, rather than with Pamphiliinae.

Two new species of Elcaninae (Orthoptera, Elcanidae) recorded from the Early Cretaceous China.

Two new species attributed to the genus Panorpidium Westwood, 1854 are described from the Lower Cretaceous Yixian Formation of Beipiao county, Liaoning province, China: Panorpidium acusicaudum sp. nov., P. validum sp. nov. The new species differs from all other known Panorpidium species by its combination of wing venation and body characters.

New Fossil Xyelidae (Hymenoptera: Symphyta) from the Mesozoic of Northeastern China

Simple SummaryOne new genus and two new species, described from new fossil specimens of northeastern China, enhance our knowledge of the Xyelidae in the mid-Mesozoic. A key to the genera of Angaridyelini and a table of known fossil species of Macroxyelinae are provided. After investigating various angles between Rs+M and 1-Rs for known fossil species of Macroxyelinae, we report that the angle and the length of 1-Rs are correlated. In addition, we believe that the tribe Ceroxyelini may have only one genus of Ceroxyela, and suggest that Isoxyela and Sinoxyela should be transferred to Gigantoxyelini.One new genus and species, Leptoxyela eximia gen. et sp. nov., and one new species, Scleroxyela cephalota sp. nov., are described and illustrated based on two well-preserved compression fossils from the Lower Cretaceous Yixian Formation and the Middle Jurassic Jiulongshan Formation of China, respectively. Leptoxyela eximia gen. et sp. nov. is placed in the tribe Angaridyelini, 1966 and Scleroxyela cephalota sp. nov. in the tribe Xyeleciini Benson, 1945; while both tribes are in the subfamily Macroxyelinae Ashmead, 1898 of Xyelidae. A key to the genera of Angaridyelini is provided. In addition, we investigated various angles between Rs+M and 1-Rs for known fossil species of Macroxyelinae, and we found the angle and the length of 1-Rs are correlated; however, we could not see any correlation between the angles and the fossil ages even within a tribe. Furthermore, based on Sc2 connected to R before Rs, the angle between Rs+M and 1-Rs, and the length of the first flagellomere, we believe that the tribe Ceroxyelini may have only one genus of Ceroxyela, and suggest that Isoxyela and Sinoxyela should be transferred to Gigantoxyelini.