Jehol Biota Research Articles

A review of vertebrate body fossils from the Korean Peninsula and perspectives

For the first time, a comprehensive review was presented for all Korean vertebrate body fossils reported during last 100 years. At present, Korean vertebrate faunas are characterized by no fossil report in the Paleozoic, various Cretaceous terrestrial vertebrates, and the Late Eocene to Middle Miocene mammals. Except for the old collection of land mammals of North Korea, most fossils have been found and published during the last three decades in South Korea. They are commonly incomplete and fragmentary. Articulated skeletons are rare except for fish fossils. Cretaceous vertebrate faunas include six freshwater fish orders (including Jinjuichthys cheongi), two families of turtles, an anguimorph lizard (Asprosaurus bibongriensis), a crocodyliform (“Hadongsuchus acerdentis”), an anurognathid pterosaur, various theropod remains including three kinds of birds, titanosauriform remains, a basal ornithopod (Koreanosaurus boseongensis), and a basal neoceratopsian (Koreaceratops hwaseongensis). Among them, pterosaur and bird specimens from the Sinuiju Series of North Korea have not been described in detail yet, but their fossil assemblages are very similar to those of Jehol Biota of northeastern China. A possibility of the faunal connection is discussed between two regions. Unfortunately, no additional mammal fossil has been reported from North Korea since two important land mammal localities were discovered in the late Eocene and early Miocene strata before 1943. However, new rodent and cetacean fossils were found in both terrestrial and marine Miocene strata in South Korea. Most of the valid vertebrate taxa appear to be endemic in Korea, but some clades show faunal affinities with Mongolia, China, and Japan. However, detailed faunal comparisons have not been performed among these countries. Vertebrate paleontological data of the Korean Peninsula have been rapidly accumulated and become crucial to understand evolutionary dynamics of vertebrates in East Asia. Vertebrate paleontological studies need to focus more on the Paleozoic strata for primitive fishes and early tetrapods, and Cenozoic terrestrial strata for land mammals in Korea. Further work throughout the geologic column will only improve our understanding of the evolution of life in East Asia.

Diversity and evolution of the Confuciusornithidae: Evidence from a new 131-million-year-old specimen from the Huajiying Formation in NE China

The Huajiying Formation contains the earliest deposits of the Jehol Biota, representing the world’s second oldest avifauna. This avifauna includes the early confuciusornithid Eoconfuciusornis zhengi, the oldest occurrence of this clade and one of the earliest divergences of pygostylian birds. Although E. zhengi shows unique traits, the holotype’s immature age makes comparisons with the better known Confuciusornis sanctus problematic. As a result, the taxonomic validity of E. zhengi is controversial. We describe a small, osteologically adult confuciusornithid from the same deposits as E. zhengi. The new fossil is most similar to E. zhengi but also shares traits with the stratigraphically younger Confuciusornis. The humerus of the new fossil is straighter and more slender, and bears a less dorsally-developed deltopectoral crest compared with similarly-sized and smaller specimens of Confuciusornis. The morphology of the humerus is intermediate between E. zhengi and Confuciusornis and its proximal portion is pierced by a small deltopectoral foramen, absent in the holotype of E. zhengi. However, this foramen is much smaller than in any other confuciusornithid. Shape analyses (geometric morphometrics) of the humerus of confuciusornithids of different ages and representatives of other basal avians and closely-related non-avian theropods supports our observations and indicate that the humeral differences between the holotype of E. zhengi and the new specimen are not easily explained as ontogenetic variation within a single species. However, the limited number of early confuciursornithids does not allow us to confidently interpret such differences as interspecific. Nonetheless, these analyses support the morphological distinctiveness of the early confuciusornithids from the Huajiying Formation and suggest a stepwise acquisition of the unique humeral morphology of Confuciusornithidae.

Countershading and Stripes in the Theropod Dinosaur Sinosauropteryx Reveal Heterogeneous Habitats in the Early Cretaceous Jehol Biota

Countershading is common across a variety of lineages and ecological time [1-4]. A dark dorsum and lighter ventrum helps to mask the three-dimensional shape of the body by reducing self-shadowing and decreasing conspicuousness, thus helping to avoid detection by predators and prey [1, 2, 4, 5]. The optimal countershading pattern is dictated by the lighting environment, which is in turn dependent upon habitat [1, 3, 5, 6]. With the discovery of fossil melanin [7, 8], it is possible to infer original color patterns from fossils, including countershading [3,9, 10]. Applying these principles, we describe the pattern of countershading in the diminutive theropod dinosaur Sinosauropteryx from the Early Cretaceous Jehol Biota of Liaoning, China. From reconstructions based on exceptional fossils, the color pattern is compared to predicted optimal countershading transitions based on 3D reconstructions of the animal's abdomen, imaged in different lighting environments. Reconstructed patterns match well with those predicted for animals living in open habitats. Jehol is presumed to have been a predominantly closed forested environment [3, 11, 12], but our results indicate a more heterogeneous range of habitats. Sinosauropteryx is also shown to exhibit a "bandit mask," a common pattern in many living vertebrates, particularly birds, that serves multiple functions including camouflage [13-18]. Sinosauropteryx therefore shows multiple color pattern features likely related to the habitat in which it lived. Our results show how reconstructing the color of extinct animals can inform on their ecologies beyond what may be obvious from skeletal remains alone. VIDEO ABSTRACT.

Flight aerodynamics in enantiornithines: Information from a new Chinese Early Cretaceous bird

We describe an exquisitely preserved new avian fossil (BMNHC-PH-919) from the Lower Cretaceous Yixian Formation of eastern Inner Mongolia, China. Although morphologically similar to Cathayornithidae and other small-sized enantiornithines from China’s Jehol Biota, many morphological features indicate that it represents a new species, here named Junornis houi. The new fossil displays most of its plumage including a pair of elongated, rachis-dominated tail feathers similarly present in a variety of other enantiornithines. BMNHC-PH-919 represents the first record of a Jehol enantiornithine from Inner Mongolia, thus extending the known distribution of these birds into the eastern portion of this region. Furthermore, its well-preserved skeleton and wing outline provide insight into the aerodynamic performance of enantiornithines, suggesting that these birds had evolved bounding flight—a flight mode common to passeriforms and other small living birds—as early as 125 million years ago.

A Mesozoic Pompeii: History of the Jehol Biota's Rise and Fall

AbstractThe Jehol fauna was initially represented by a bony fish, concostracan and an insect, as a Lycoptera davidi–Eosestheria–Ephemeropsis trisetalis association, but since the researches of recent decades, the Jehol Biota is now completely different from the past low‐diversity, and encompasses a native terrestrial biota that includes many well‐preserved vertebrates, invertebrates and plants. There are more than 20 important biological categories, thousands of taphonomically unusual fossils, especially noted for the wide variety of biological tissues. The Jehol Biota has caused a sensation in the world with its wide distribution, large quantity, great variety, fine preservation and detailed information, which records the rise and fall of the numerous taxa, and provides significant evidence for three origins: of birds, eutherian mammals, and angiosperms. The Jehol Biota is a highlight of basic scientific research in China, and we honor it as a world–class fossil treasury and “a Mesozoic Pompeii”.

First Discovered Diversified Fossil Locality of the Jehol Biota in the Greater Khingan Mountains, Inner Mongolia

First Discovered Diversified Fossil Locality of the Jehol Biota in the Greater Khingan Mountains, Inner Mongolia

New chronostratigraphic constraints on the Yixian Formation with implications for the Jehol Biota

The fossils of the Cretaceous Jehol Biota exhibit excellent preservation and extraordinary diversity. Terrestrial fossils, including plants, insects, dinosaurs, birds, mammals and freshwater invertebrates have been discovered from the Dabeigou, Yixian and Jiufotang Formations (and correlative strata) in Central and East Asia. Significant specimens have been recovered from the Yixian Formation of Inner Mongolia, Hebei Province, western Liaoning Province of NE China. The Yixian Formation is generally divided (from bottom to top) into the Lujiatun Unit, Lower Lava Unit, Jianshangou Unit, Upper Lava Unit, Dawangzhangzi Unit and Jingangshan Unit. However, previously reported age data obtained through a range of methods and applied to different units of the Yixian Formation do not consistently integrate with the Yixian's commonly accepted stratigraphic interpretation. Here we summarize previous age data for the Yixian Formation and recalibrate previously reported 40Ar/39Ar ages by using new age interpretations for the same standard (i.e. FCs=28.294). We also present new high-precision 40Ar/39Ar ages of 125.8±1.0Ma and 126.0±0.8Ma for two basaltic samples from the Lujiatun Unit, a unit of previously uncertain age. The new age data and re-calibrated published data indicate that the Lujiatun Unit was deposited contemporaneously with the Jianshangou Unit. The widely accepted stratigraphic column for the Yixian Formation therefore requires reinterpretation. Our study provides significant clues for reconstructing sedimentary environment for the fossil-rich Yixian deposits and allows to constrain evolutionary rates for early mammals, primitive birds and feathered dinosaurs.

The toothless pterosaur Jidapterus edentus (Pterodactyloidea: Azhdarchoidea) from the Early Cretaceous Jehol Biota and its paleoecological implications.

BackgroundIn the Early Cretaceous Jehol Biota, the toothless pterosaurs flourished with the chaoyangopterids and tapejarids playing a key role in understanding the early diversity and evolution of the Azhdarchoidea. Unlike the more diverse tapejarids, the rarer chaoyangopterids are characterized by a long and low rostrum, supporting a close relationship with the huge azhdarchids. Unfortunately, our knowledge is still limited in the osteology, paleoecology, and taxonomy of the Chaoyangopteridae. As one of the best preserved skeletons, the type and only specimen of Jidapterus edentus provides an opportunity to understand the morphology and paleoecology of the chaoyangopterids.ResultsOur study of the osteology of Jidapterus edentus reveals valuable information about the morphology of the Chaoyangopteridae such as a rostrum with a curved dorsal profile, high Rostral Index (RI), larger angle between the dorsal and postorbital processes of the jugal, sequentially shorter fourth to seventh cervical vertebrae, sternum with a plate wider than long, contact of the metacarpal I with the distal syncarpal, pneumatic foramen on first wing phalanx, hatchet-like postacetabular process with unconstricted neck and small dorsal process, distinctly concave anterior margin of pubis, subrectangular pubic plate with nearly parallel anterior and posterior margins, longer proximal phalanges of pedal digits III and IV, as well as reduced and less curved pedal unguals. These features further support the validity of Jidapterus edentus as a distinct species and the close relationship of the chaoyangopterids with the azhdarchids. Paleoecologically, the chaoyangopterids are probably like the azhdarchids, more terrestrial than the contemporaneous and putatively arboreal tapejarids, which may have been limited to the forest-dominated ecosystem of the Jehol Biota.DiscussionThe osteology of Jidapterus edentus further supports the close relationship of the Chaoyangopteridae with the Azhdarchidae in sharing a high RI value and reduced and mildly-curved pedal unguals, and it also implies a possible paleoecological similarity in their terrestrial capability. Combined with the putatively arboreal and herbivorous tapejarids, this distinct lifestyle of the chaoyangopterids provides new insights into the diversity of pterosaurs in the ecosystem of the Jehol Biota.

Cervical vertebrae of an enigmatic pterosaur from the Crato Formation (Lower Cretaceous, Araripe Basin, NE Brazil)

Abstract The Brazilian Crato Formation (Lower Cretaceous, Aptian) is well known for its rich pterosaur fauna. This paper deals with a new find represented by four articulated mid-cervical vertebrae. The vertebrae show a morphology consistent with that seen in the Chaoyangopteridae, especially the relative elongation, low neural spines, lack of pneumatic foramina on the lateral face of the centra and the presence of well-developed postexapophyses. Chaoyangopterids are, so far, represented with confidence only in Chinese deposits; the only record outside the Jehol Group is the Crato Formation form Lacusovagus magnificens , a partial skull whose assignment to the Chaoyangopteridae has been disputed. Given this controversy, we review the phylogenetic position of Lacusovagus , and discuss the nesting of our new specimen among theChaoyangopteridae, providing some comments concerning the composition of the group. We conclude that our new specimen provides further support for the presence of chaoyangopterids in the Early Cretaceous of Brazil.

Mosaic evolution in an asymmetrically feathered troodontid dinosaur with transitional features

Asymmetrical feathers have been associated with flight capability but are also found in species that do not fly, and their appearance was a major event in feather evolution. Among non-avialan theropods, they are only known in microraptorine dromaeosaurids. Here we report a new troodontid, Jianianhualong tengi gen. et sp. nov., from the Lower Cretaceous Jehol Group of China, that has anatomical features that are transitional between long-armed basal troodontids and derived short-armed ones, shedding new light on troodontid character evolution. It indicates that troodontid feathering is similar to Archaeopteryx in having large arm and leg feathers as well as frond-like tail feathering, confirming that these feathering characteristics were widely present among basal paravians. Most significantly, the taxon has the earliest known asymmetrical troodontid feathers, suggesting that feather asymmetry was ancestral to Paraves. This taxon also displays a mosaic distribution of characters like Sinusonasus, another troodontid with transitional anatomical features.

The first juvenile specimen of Manchurochelys manchoukuoensis from the Early Cretaceous Jehol Biota.

A small juvenile turtle is described from the Early Cretaceous Jehol Biota, shedding light on the juvenile morphology and ontogeny of Manchurochelys manchoukuoensis. Several juvenile features are uncovered, such as a small and circular carapace (less than half of the adult), wide vertebral scales, and lateral carapacial fontanelles. In contrast to the adult morphology, which has an oval carapace, closed lateral fontanelles, and longer vertebrals 2–4, the juvenile of M. manchoukuoensis is more comparable to that of Sinemys lens, except for earlier occurrence of the well-ossified carapace of the latter. Differs from Changmachelys bohlini, and Ordosemys liaoxiensis, in which the circular carapace is relatively independent of ontogenetic age, and the lateral fontanelles are only closed in adult stage of O. liaoxiensis. Therefore, the trajectory of ontogenetic change appears to be highly diversified in the sinemydids.

A New Crown-Group Frog (Amphibia: Anura) from the Early Cretaceous of Northeastern Inner Mongolia, China

ABSTRACT Based on 12 well-preserved skeletons of postmetamorphic individuals, a new crown-group frog taxon is named and described from the Lower Cretaceous Guanghua (upper part of Longjiang) Formation (stratigraphic equivalent of the world-famed Yixian Formation) exposed in Dayangshu Basin, Hulunbuir, in the far northeast of Inner Mongolia, China. The new taxon, Genibatrachus baoshanensis, documents another Early Cretaceous anuran having reduction of the presacral vertebrae to eight in number, similar to several frog taxa of roughly the same age from Spain and Brazil. The new frog also displays several features that are ontogenetically and phylogenetically informative, including ontogenetic fusion of the palatine to the sphenethmoid, and ontogenetic fusion of ribs to the diapophyses of the posterior trunk vertebrae. In addition, the new discovery extends the geographic range of Early Cretaceous frogs of the Jehol Biota northward to near the 50th parallel north in East Asia.

SEM morphological study of the type species of Ordosestheria Wang, 1984 (Spinicaudata) from Ordos Basin of mid-west China

SEM morphological study of the type specimens of Ordosestheria wujiamiaoensis Wang, 1984 from the non-marine lower Aptian Jingchuan Formation in Inner Mongolia of the Ordos Basin in mid-west China has revealed taxonomic features not previously seen: 1) a row of small pits along the lower margin of each growth band in the lower part of the carapace; 2) growth lines are serrated in their lower margins; 3) a row of small pores on each growth line may indicate that through which a row of setae has developed. In consideration of the first occurrence of Ordosestheria from the lower Barremian of southern Tunisia, ordosestheriids may most likely have originated in North Africa and then dispersed to eastern Asia in early Aptian, and became a member of the well-known Jehol Biota.

Vertebrate assemblages of the Jurassic Yanliao Biota and the Early Cretaceous Jehol Biota: Comparisons and implications

Although both the Yanliao and Jehol vertebrate assemblages are known for exceptional preservation of feathered dinosaurs, mammals, pterosaurs, lizards, salamanders, and fish, the Early Cretaceous Jehol Biota also contains birds, choristoderes, frogs, and turtles that are currently lacking in the Jurassic Yanliao Biota. The vertebrate assemblages of the Yanliao and Jehol biotas are very distinct from each other, with the salamander Liaoxitriton being the sole unquestionably shared taxon on generic level. Both assemblages contain mainly stem relatives of major clades of extant vertebrates, with all genera and species extinct. Crown group taxa are restricted to some fishes, salamanders, frogs, and turtles.In addition to its much greater taxonomic diversity, the Jehol vertebrate assemblage also shows a greater body size variation among dinosaurs, pterosaurs, and mammals (three major vertebrate groups shared by the two biotas); however, members of these groups are generally small in the Yanliao Biota. The Jehol aquatic vertebrates also show a much greater diversity, characterized by many large-sized forms such as acipenseriforms and choristoderes, possibly indicating growing and more expanded ecological adaptations of the Jehol vertebrates.The relatively greater biodiversity of pterosaurs in the Yanliao Biota as compared to that in the Jehol Biota was due possibly to the lack of birds as a competitor then. Birds in the Jehol Biota had occupied much of the similar ecological niches (forest, lakes etc.) with more sophisticated and refined flight capability.The Yanliao dinosaurs that were dominated by maniraptorans are either paravians or closely related species, possibly indicating that northeastern China could be an origin center of the earliest birds, consistent with the previous hypothesis that this area was probably also the origin and diversification center for many other biological groups.The flourishing time of the Jehol Biota (125 Ma) appears to be coincident with the peak of the destruction of the North China Craton, and the flourishing time of the Yanliao Biota (160 Ma) is coincident with the initiation time of the destruction of the North China Craton or the beginning of the subduction of the Paleo-Pacific plate underneath the Asian continent that resulted a series of tectonic and palaeogeographic and palaeoenvironmental changes, confirming the co-evolution between the two biotas and their geological and palaeoenvironmental background. The frequent volcanic activities during the formation of both the Yanliao and Jehol biotas not only provided much nutrient to the lakes, but also were critical for the exceptional soft tissue preservation of the two lagerstätten.The cold temperature or the fluctuation of temperature during the Middle Jurassic–Late Jurassic transition might be related to the first appearance of feathered dinosaurs and haired pterosaurs. The cold interval during the Early Cretaceous Jehol Biota could possibly partially explain the presence of many feathered dinosaurs including some large-sized theropods.

A new lizard (Reptilia: Squamata) from the Lower Cretaceous Yixian Formation of China, with a taxonomic revision of Yabeinosaurus

Yabeinosaurus was the first lizard genus described from the Early Cretaceous Jehol Biota of China. The holotype of the type species, Y. tenuis, is an immature skeleton but it has been lost for decades. A second species, Y. youngi, was erected based on another immature skeleton and is distinguished by its longer, more gracile limbs. In 2001, a juvenile skeleton from the Jingangshan locality of Liaoning was designated as the neotype for Y. tenuis. Subsequently, several further specimens from other localities, juvenile and adult, have been attributed to this species. Here we describe a second lizard specimen from the neotype locality. In anterior tooth shape, finger-like mandibular angular process, cranial sculpture, maxilla shape, and short, robust humerus, the new specimen resembles adult and subadult material currently attributed to Y. tenuis, but it differs in having bicuspid posterior teeth and a straight rather than a hooked angular process of the mandible. We propose a new species (Y. bicuspidens sp. nov.) for this specimen which represents the first occurrence of bicuspid teeth in an Early Cretaceous lizard from China. However, the recognition of a second species at the neotype locality raises a taxonomic problem. Due to the immaturity of the designated holotype and neotype of Y. tenuis, they cannot be coded for the jaw and dental characters that distinguish the two robust-limbed species. This renders Yabeinosaurus tenuis a nomen dubium. Here we propose that Yabeinosaurus tenuis should be treated as a historic taxon, permitting retention of the generic name under ICZN rules, and erect a second new species (Y. robustus sp. nov.) for the principal robust-limbed morphotype in the Jehol Biota with monocuspid posterior teeth and a hooked angular process.

Complexities and novelties in the early evolution of avian flight, as seen in the Mesozoic Yanliao and Jehol Biotas of Northeast China

Recently reported specimens from the Mid-Late Jurassic Yanliao (or Daohugou) Biota and Early Cretaceous Jehol Biota of Northeast China suggest that the early evolution of avian flight involved a surprising amount of homoplasy and evolutionary experimentation. Pennaceous feathers of variable size, structure, and extent occur on the hindlimbs of numerous Jehol and Yanliao paravian theropods, including some basal birds, and clearly had an aerodynamic function at least in the dromaeosaurid Microraptor. However, their function in many cases may have been primarily ornamental, and it is unclear whether aerodynamically useful hindwings represent a widespread paravian feature or an evolutionary novelty limited to Microraptor and possibly a few other taxa. Clearer examples of novelties related to aerial locomotion are the tail plumage of the basal bird Jeholornis, in which a proximal fan of feathers is present and the ancestral distal frond is somewhat reduced, and the membranous wings of the Yanliao scansoriopterygid Yi. Early paravian evolution evidently involved a rapid diversification of aerodynamic structures, and ancestral paravians may have been volant. It is also possible that the avian lineage passed through a four-winged “tetrapterygian” stage, but current phylogenies suggest that aerodynamic hindwings were more likely acquired independently by different paravian groups.

Laser Fluorescence Illuminates the Soft Tissue and Life Habits of the Early Cretaceous Bird Confuciusornis.

In this paper we report the discovery of non-plumage soft tissues in Confuciusornis, a basal beaked bird from the Early Cretaceous Jehol Biota in northeastern China. Various soft tissues are visualized and interpreted through the use of laser-stimulated fluorescence, providing much novel anatomical information about this early bird, specifically reticulate scales covering the feet, and the well-developed and robust pro- and postpatagium. We also include a direct comparison between the forelimb soft tissues of Confuciusornis and modern avian patagia. Furthermore, apparently large, fleshy phalangeal pads are preserved on the feet. The reticulate scales, robust phalangeal pads as well as the highly recurved pedal claws strongly support Confuciusornis as an arboreal bird. Reticulate scales are more rounded than scutate scales and do not overlap, thus allowing for more flexibility in the toe. The extent of the pro- and postpatagium and the robust primary feather rachises are evidence that Confuciusornis was capable of powered flight, contrary to previous reports suggesting otherwise. A unique avian wing shape is also reconstructed based on plumage preserved. These soft tissues combined indicate an arboreal bird with the capacity for short-term (non-migratory) flight, and suggest that, although primitive, Confuciusornis already possessed many relatively advanced avian anatomical characteristics.

Molecular evidence of keratin and melanosomes in feathers of the Early Cretaceous bird Eoconfuciusornis

Microbodies associated with feathers of both nonavian dinosaurs and early birds were first identified as bacteria but have been reinterpreted as melanosomes. Whereas melanosomes in modern feathers are always surrounded by and embedded in keratin, melanosomes embedded in keratin in fossils has not been demonstrated. Here we provide multiple independent molecular analyses of both microbodies and the associated matrix recovered from feathers of a new specimen of the basal bird Eoconfuciusornis from the Early Cretaceous Jehol Biota of China. Our work represents the oldest ultrastructural and immunological recognition of avian beta-keratin from an Early Cretaceous (∼130-Ma) bird. We apply immunogold to identify protein epitopes at high resolution, by localizing antibody-antigen complexes to specific fossil ultrastructures. Retention of original keratinous proteins in the matrix surrounding electron-opaque microbodies supports their assignment as melanosomes and adds to the criteria employable to distinguish melanosomes from microbial bodies. Our work sheds new light on molecular preservation within normally labile tissues preserved in fossils.

First species of Enantiornithes from Sihedang elucidates skeletal development in Early Cretaceous enantiornithines

The Sihedang locality of the Lower Cretaceous Yixian Formation is the only recognized ornithuromorph-dominated locality in the Jehol Group of north-eastern China. Here we report on the first enantiornithine from this locality and erect a new taxon Monoenantiornis sihedangia gen. et sp. nov. The holotype and only specimen preserves a rare ontogenetic stage in which the intermedium is ossified but free from the other proximal tarsals and the tibia, consistent with the pattern of ossification that occurs in neornithines. In order to explore the pattern of skeletal development in the enantiornithines, we select several published specimens inferred to represent different ontogenetic stages and document their degree of fusion in five key compound bones and the sterna. This provides a preliminary hypothesis for the sequence in which compound bones form in Early Cretaceous enantiornithines. From this hypothesis, most known specimens can be categorized into four major ontogenetic stages: all the compound bones unfused; synsacrum and pygostyle fused; tarsals fused; tibiotarsus and carpometacarpus formed.http://zoobank.org/urn:lsid:zoobank.org:pub:347485CA-87E6-4834-BEB5-687B6798644E

Fauna and flora of Early Cretaceous Tetori Group in Central Japan: The clues to revealing the evolution of Cretaceous terrestrial ecosystem in East Asia

The Early Cretaceous Tetori Group in northern Central Japan was deposited in the eastern margin of the Asian Continent at mid-latitudes. It consists of two depositional stages: DS2 (Berriasian–late Hauterivian; mainly brackish environment with intercalations of marine horizons) and DS3 (Barremian–Aptian; freshwater environments only). Review of their faunal and floral compositions reveals that (1) two vertebrate fossil localities in DS3: Kaseki-kabe (upper part of the Kuwajima Formation) and Kitadani Dinosaur Quarry (Kitadani Formation) are assigned to the Barremian and the Aptian, respectively, and probably coeval to the Jehol Group in the Liaoning, northern China; (2) abundant freshwater bivalves occur in DS3, and the Trigonioides–Plicatounio–Nippononaia (TPN) assemblage is present only in the Kitadani Formation; and (3) stratigraphic change of plant assemblages in DS3 indicates that climatic change (warmer and dryer) occurred around the Barremian–Aptian boundary, which is concordant with the faunal change inferred from the choristodere-bearing assemblage in the Okurodani and Kuwajima formations to the crocodyliform-bearing assemblage in the Kitadani Formation. Vertebrate and invertebrate faunal as well as floral compositions of the Tetori Group are distinct from those of the Jehol Group. Paleoclimatic and/or paleogeographical conditions were probably different between two regions, and thus paleobiogeographical differentiation in East Asia is suggested in the Early Cretaceous.