A review of bipolarity concepts: History and examples from Radiolaria and Medusozoa (Cnidaria)

Bipolarity, its history and general interpretation are investigated and discussed herein. Apart from the classical view, namely that a bipolar distribution is a peculiar biogeographical phenomenon, we propose that it is ecologically controlled too. This approach was used for bipolarity assessment within the following groups: Phaeodaria, Nassellaria, Spumellaria (Radiolaria) and Medusozoa (Cnidaria). We recognize 46 bipolar radiolarian species and three radiolarian genera. However, although species concepts in radiolarians are relatively stable and well known, the high-rank taxonomy of radiolarians is still not well defined. Caution should therefore be taken in the interpretation of distribution data at a taxonomic level higher than the species. In the Medusozoa, bipolarity is observed for 23 species and 32 genera. The different ways in which bipolarity can develop are discussed under the different groups, but preference has been given to the recent and most probable routes of migration. In our investigation of the bipolarity phenomenon, we reviewed more than 400 articles dealing with taxonomy, ecology and biogeography of the modern fauna in both groups.     

Taxonomic study of the tetrahedral, pentagonal and hexagonal spongy spumellarian Radiolaria from the middle Carnian (Late Triassic) of the Köseyahya nappe (Elbistan, SE Turkey) and other Triassic localities

This article is a taxonomic study of all spongy radiolarian taxa with five to six coplanar and four tetrahedrally disposed spines or spongy arms occurring in the middle Carnian from the Köseyahya section, near the town of Elbistan, SE Turkey. This fauna is characteristic of the Tetraporobrachia haeckeli radiolarian Zone, and comes from an 8 m thick succession of clayey–cherty limestones occurring at the lower part of the section. In addition, a few species from the Middle and Upper Triassic from other areas have been also included in this study to improve some generic diagnoses and to better understand the diversity and evolutionary trends of some genera, subfamilies and families. The taxonomy at the generic and suprageneric levels is based primarily on the types of microsphere. This new approach allowed new taxonomic arrangements of genera and suprageneric units, and suggested new and unexpected phylogenetic relationships among these radiolarians and between them and younger radiolarians. The authors discuss and describe 42 species, of which 36 are new, and 12 genera of which three are new (Charlottalum, Pentaspongodisculus, and Trimiducaella). The genera Pseudohagiastrum Pessagno, Natraglia Pessagno, Cantalum Pessagno and others are reinterpreted. All the genera studied, except Charlottalum, are assigned to three subfamilies, of which two (Pseudohagiastrinae and Trimiducinae) are new, and to two families (Angulobracchiidae and Relindellidae). The genus Charlottalum is described to replace the genus Cantalum, which has been erroneously used until present for Late Triassic pantanelliids with four tetrahedrally disposed three-bladed spines.     

Discovery of Middle Jurassic (Bajocian) Radiolaria from the sedimentary cover of the Vedi ophiolite (Lesser Caucasus,Armenia)

The Vedi ophiolite, situated southeast of Yerevan (Armenia), represents part of the Neotethyan oceanic lithosphere preserved in the Lesser Caucasus. This ophiolite unit constitutes a large tectonic klippe, a result of obduction during the Upper Cretaceous (Coniacian–Santonian). Relatively well-preserved Radiolaria extracted from radiolarites overlying ophiolitic lavas along the Vedi River consist of Middle Jurassic (Bajocian, U.A.Z. 3–4) species, typical of the Tethyan tropical bioprovince. Assemblages are dominated by Nassellaria and characterised by the presence of species Cyrtocapsa mastoidea, Hexasaturnalis hexagonus, Laxtorum (?) hichioense, Stichocapsa japonica and Striatojaponocapsa plicarum s.l. This microfauna provides evidence for the oldest age available so far for the sedimentary cover of the Vedi ophiolite.     

Mesozoic Radiolaria of Bosnia and Serbia: New data

Jurassic and Cretaceous radiolarian faunas were discovered in bedded chert of the Dinaric and Vardar tectonic zones of Bosnia and Herzegovina. Only Triassic radiolarians have previously been described in Bosnia and Herzegovina, while the finds of Bajocian, Bathonian-Callovian, Oxfordian-Kimmeridgian, Tithonian-Berriasian, and Campanian are new. Additional localities of Triassic and Jurassic radiolarians were investigated in Serbia. By correlation with radiolarians from the previous studies within Serbia, the Late Aalenian-Bajocian and Bathonian-Callovian Serbian radiolarian beds are newly dated. The first find of Cretaceous radiolarians in Serbia is reported. The oldest Mesozoic Radiolaria-bearing formations outcropping in the Western Belt of the Vardar Zone are dated Mid-Upper Triassic. The youngest radiolarians come from the Upper Cretaceous (Campanian) of the northern part of this belt of the Vardar Zone, where they co-occur with planktonic foraminifers. The distribution of 70 radiolarian samples within sections is shown. The taxonomic composition of 39 samples is analyzed. Radiolarian species extracted from 13 samples are described and figured. The list of 72 taxa and 3 plates of Jurassic radiolarians of Bosnia and Herzegovina, 3 plates of Triassic, 1 plate of Middle Jurassic, and 1 plate of Upper Cretaceous radiolarians of Serbia are presented.     

Taxonomic study of spongy spumellarian Radiolaria with three and four coplanar spines or arms from the middle Carnian (Late Triassic) of the Köseyahya nappe (Elbistan, SE Turkey) and other Triassic localities

The present article is a taxonomic study of all spongy spumellarian radiolarian taxa with three and four coplanar spines or spongy arms occurring in the middle Carnian from the Köseyahya section, near the town of Elbistan, SE Turkey. This fauna is characteristic of the Tetraporobrachia haeckeli radiolarian Zone, and comes from an 8 m thick succession of clayey-cherty limestones occurring at the lower part of the section. In addition, a few species from the Middle and Upper Triassic from other areas have been also included in this study to improve some generic diagnoses, and to better comprehend the diversity and evolutionary trends of some genera, subfamilies and families. The taxonomy at the generic and suprageneric levels is based primarily on the types of microsphere. This new approach allowed new taxonomic arrangements of genera and suprageneric units, and suggested new phylogenetic relationships among these radiolarians and between them and younger radiolarians. The authors discuss and describe 69 species, of which 37 are new, and 14 genera, of which three are new (Paraparonaella, Pseudangulobracchia, and Ropanaella). The genus Triassoastrum and others are reinterpreted. All genera studied are assigned to five subfamilies, of which two are new (Tetrapaurinellinae and Triassocrucellinae), and two families (Tritrabidae and Veghicycliidae). Nine species in open nomenclature are also illustrated.     

Lower Jurassic corals from the Pamir Mountains,Central Asia

The paper describes new Lower Jurassic corals from the South-Eastern Pamir Mountains (Tajikistan) and interprets their relationships with contemporaneous West Tethyan corals. Taxonomic similarities with Pliensbachian European and North African faunas indicate a Pliensbachian age for this fauna, which was previously considered to be of Hettangian/Sinemurian age. Together with the taxa earlier described from the Pamirs, this fauna consists of 30 species of 25 genera, including Triassic holdover genera such as Stylophyllopsis, Phacelostylophyllum and Eocomoseris. The bulk of the fauna represents new Jurassic genera: Alichurastrea, Eomicrophyllia, Guembelastreomorpha, Gurumdynia, Pinacomorpha, Protostephanastrea, Psenophyllia, Sedekastrea and Stylimorpha. Earlier coral studies of the region concerned the genera: Archaeosmilia Melnikova, 1975, Archaeosmiliopsis Melnikova, 1975, Cylismilia Roniewicz, 1988, Pachysmilia Melnikova, 1989, and Prodonacosmilia Melnikova in Melnikova and Roniewicz, 1976. Two species that were considered to belong to the genus Cylismilia, are redescribed and reclassified in the genera Psenophyllia, and Archaeosmilia Melnikova, respectively.     

New and little-known grylloblattids of the family Geinitziidae (Insecta: Grylloblattida) from the Triassic and Jurassic of Europe,Asia, and South Africa

The fossil history of the family Geinitziidae is reviewed. New taxa are described in the family: Shurabia hissarica, sp. nov. (Lower Jurassic of Tajikistan), Sh. shartegica, sp. nov. (Upper Jurassic of Mongolia), Sh. serrata, sp. nov. and Ginitzia sagulensis, sp. nov. (both Lower Jurassic of Kyrgyzstan). The subfamily Stegopterinae Sharov, 1961 is synonymized under Geinitziinae Handlirsch, 1906. The genera Minesedes Fujiyama, 1973 and Ominea Fujiyama, 1973 (Upper Triassic of Japan) are synonymized under Shurabia Martynov, 1937 and Geinitzia Handlirsch, 1906, respectively. Geinitzia varia Bode, 1953 (Lower Jurassic of Germany) and Fletchizia picturata Riek, 1976 (Upper Triassic of South Africa) are redescribed from their holotypes. F. kapokraalensis Wappler, 2001 and F. aleda Wappler, 2001 (both Upper Triassic of South Africa) are transferred to the genus Shurabia.     

Early Tithonian Saturnalidae (Radiolaria) from the Solnhofen area (Southern Franconian Alb, southern Germany)

In order to complete the study of the very rich early Tithonian (Hybonoticeras hybonotum Zone) radiolarian fauna from the Mühlheim Member of the Mörnsheim Formation outcropping in the Solnhofen area, the taxa of the family Saturnalidae are described. Although rather rare, the Saturnalidae of this member contain 14 species, ten of which are new. These species belong to four genera, one of which is new (Moebicircus n. gen.), and two subfamilies (Hexasaturnalinae and Saturnalinae). The taxonomy at generic level of these late Jurassic radiolarians is founded on the basis of the position of the blades along the ring and number and morphology of the spines. Type of spines (simple or forked) has either species level value or none, depending on species. Special attention was given to anomalies, which sometimes are rather frequent, since they can give Information of paleobiological and paleoecological Orders. Among them frequent cases of open ring and additional spines withDicerosaturnalis and Siamese twins skeletons withSpongosaturninus andDicerosaturnalis are to be noted. The authors hope that this new taxonomy will give a better image of the evolution and radiation of the Saturnalidae during the Tithonian.     

Floral Assemblages and Patterns of Insect Herbivory during the Permian to Triassic of Northeastern Italy

To discern the effect of the end-Permian (P-Tr) ecological crisis on land, interactions between plants and their insect herbivores were examined for four time intervals containing ten major floras from the Dolomites of northeastern Italy during a Permian–Triassic interval. These floras are: (i) the Kungurian Tregiovo Flora; (ii) the Wuchiapingian Bletterbach Flora; (iii) three Anisian floras; and (iv) five Ladinian floras. Derived plant–insect interactional data is based on 4242 plant specimens (1995 Permian, 2247 Triassic) allocated to 86 fossil taxa (32 Permian, 56 Triassic), representing lycophytes, sphenophytes, pteridophytes, pteridosperms, ginkgophytes, cycadophytes and coniferophytes from 37 million-year interval (23 m.yr. Permian, 14 m.yr. Triassic). Major Kungurian herbivorized plants were unaffiliated taxa and pteridosperms; later during the Wuchiapingian cycadophytes were predominantly consumed. For the Anisian, pteridosperms and cycadophytes were preferentially consumed, and subordinately pteridophytes, lycophytes and conifers. Ladinian herbivores overwhelming targeted pteridosperms and subordinately cycadophytes and conifers. Throughout the interval the percentage of insect-damaged leaves in bulk floras, as a proportion of total leaves examined, varied from 3.6% for the Kungurian (N = 464 leaves), 1.95% for the Wuchiapingian (N = 1531), 11.65% for the pooled Anisian (N = 1324), to 10.72% for the pooled Ladinian (N = 923), documenting an overall herbivory rise. The percentage of generalized consumption, equivalent to external foliage feeding, consistently exceeded the level of specialized consumption from internal feeding. Generalized damage ranged from 73.6% (Kungurian) of all feeding damage, to 79% (Wuchiapingian), 65.5% (pooled Anisian) and 73.2% (pooled Ladinian). Generalized-to-specialized ratios show minimal change through the interval, although herbivore component community structure (herbivore species feeding on a single plant-host species) increasingly was partitioned from Wuchiapingian to Ladinian. The Paleozoic plant with the richest herbivore component community, the coniferophyte Pseudovoltzia liebeana, harbored four damage types (DTs), whereas its Triassic parallel, the pteridosperm Scytophyllum bergeri housed 11 DTs, almost four times that of P. liebeana. Although generalized DTs of P. liebeana were similar to S. bergeri, there was expansion of Triassic specialized feeding types, including leaf mining. Permian–Triassic generalized herbivory remained relatively constant, but specialized herbivores more finely partitioned plant-host tissues via new feeding modes, especially in the Anisian. Insect-damaged leaf percentages for Dolomites Kungurian and Wuchiapingian floras were similar to those of lower Permian, north-central Texas, but only one-third that of southeastern Brazil. Global herbivore patterns for Early Triassic plant–insect interactions remain unknown.     

On the status of the Permian radiolarian genus Multisphaera Nazarov and Afanasieva, 2000

Based on the detailed morphological study of the type species of the genus Multisphaera Nazarov and Afanasieva, the author emends the status and diagnosis of this genus and of the subfamily Multisphaerinae Nazarov and Afanasieva. He found that the initial spicule of the type species is not multi-rayed, as initially thought, but a tetrahedral spicule. Accordingly, the genus is assigned to the former tribe Tetrentactiniini Kozur and Mostler that is herein raised to the family rank and comprises all Upper Devonian to lower Permian genera with a tetrahedral initial spicule. Consequently, the subfamily Multisphaerinae is considered a junior synonym of the family Tetrentactiniidae. To better solve the taxonomic problems of this family the author compares the morphological diversity of its members with the morphological diversity of the lower Tithonian (uppermost Jurassic) tetrahedral spicule-bearing entactinarian Radiolaria occurring in the Solnhofen area, southern Germany. Although these genera have the same type of spicule as the Paleozoic ones, they seem to belong to a new family because between the lower Tithonian and the lower Permian genera there is a long time interval of about 120 Ma in which no radiolarians with a tetrahedral initial spicule have been recorded so far. This comparison shows once more the conservative character of the initial spicule and the wide morphological diversity of the extraspicular shell.     

Ladinian radiolarian fauna from West Sichuan, China

A poorly preserved, but diversified radiolarian fauna was recovered from thin-bedded cherts occurring in the southeast of Daofu, Sichuan Province, southwestern China. Twenty-two radiolarian species belonging to 10 genera are identified and three new species (Paroertlispongus daofuensis n. sp., Falcispongus heinzi n. sp., Falcispongus pauliani n. sp.) are described. Falcispongus heinzi represents a transitional species between genera Oertlispongus inaequispinosus Dumitrica, Kozur and Mostler and Falcispongus Dumitrica. The fauna is divided into two assemblages, namely Muelleritortis cochleata and Oertlispongus inaequispinosus assemblages, which can be well correlated with the Ladinian radiolarian zones from Europe. The fauna indicates that basaltic rocks occurring in the Xianshuihe Belt were formed mainly during the Middle Triassic. Our results thus extend the previously known geological age of the Xianshuihe Belt to the Middle and Late Triassic interval.     

Zygopleuroidea (Gastropoda) aus dem Lias und Dogger Deutschlands und Nordwestpolens

16 taxa of gastropods are described from the Lower and Middle Jurassic of Germany and northwestern Poland. They belong to seven genera. Two species (Pommerozygia aspera, Costazygia bilzi) and two genera (Brevizygia, Costazygia) are new. The family Pommerozygiidae is new as well. Compared to the Zygopleuridae, the Pommerozygiidae have a rather short and broad shell with only few teleoconch whorls. The protoconch is broad conical with a rounded apex (because the first whorls are nearly planispiral). From the Zygopleuridae only members of the Zygopleurinae have been found. Most Jurassic species have a smooth protoconch. Within the Zygopleuridae, the development possibly began with protoconchs carrying collabral axial ribs (and spirals) and led to smooth protoconchs. The genera of the Pommerozygiidae are rather similar to each other. The planktotrophic larval shell has a subsutural row of nodes like many species of Triassic Zygopleuridae. Therefore, both families are closely related. The Pommerozygiidae are possibly a separate branch of the Zygopleuroidea without descendants. The main branch is probably the evolutionary line Zygopleuriidae — Janthinoidea.     

New fossils of ascomycetous anamorphic fungi from Baltic amber

Three new fossils of saprotrophic fungi are presented and described from Baltic amber, dated to Eocene epoch (Paleogene, upper to mid-Eocene). All belong to Ascomycota and are represented by hyphae as well as asexual reproduction structures allowing to assign them to present genera, respectively Periconia, Penicillium and Scopulariopsis. These material provide both the first and the oldest known fossil record of the mentioned taxa, making these data valuable for the knowledge about the evolutionary history of the Ascomycota.     

New finds ofOmphalosaurus and a review of Triassic ichthyosaur paleobiogeography

Triassic ichthyosaurs are very widespread and diverse but most taxa are poorly known. New discoveries, such as described in this paper, underscore the first statement but only slowy invalidate the second. The first associated skeleton of the unusual durophagous ichthyosaurOmphalosaurus (O. wolfi) is reported from the Middle Triassic (earliest Ladinian) of the northern Alps. The vertebrae are of the ichthyosaurian type, firmly establishing the ichthyosaurian affinities of the genus. A round bone from the Muschelkalk of Franconia, Germany, is identified and described as a left humerus ofOmphalosaurus sp. These finds greatly extend the paleogeographic and temporal range ofOmphalosaurus which previously was only known from the western cratonic margin of North America and from Spitsbergen. The new records ofOmphalosaurus allow a revised differential diagnosis of the genus and a revision of its species. Valid species ofOmphalosaurus areO. nettarhynchus, O. nevadanus, andO. wolfi. In conjunction with such new insights into Triassic ichthyosaur distribution, it is necessary to address the validity of the poorly known genera such as the Middle TriassicPessosaurus. This taxon must be considered invalid because it lacks diagnostic characters. In assessing progress in research on Triassic ichthyosaurs and their paleobiogeography, it becomes apparent that supra-specific diversity appears largely known, at least for the pre-Norian record of North America, Europe, and East Asia.     

New evidence of nearshore Mid-Triassic <Emphasis Type="Italic">Zoophycos</Emphasis>: morphological and paleoenvironmental characterization

Zoophycos is a well-known trace fossil common throughout the Phanerozoic. Paleozoic forms show important differences in morphology and habitat distribution with respect to the Jurassic, Cretaceous, and Cenozoic ones. Therefore, Early–Middle Triassic is considered a crucial time-span for the understanding of the evolution of this trace fossil. So far, Early Triassic Zoophycos is unknown and Middle Triassic forms were recorded only in deposits from Thuringia. The morphology and paleoenvironment of Zoophycos from the middle–upper Muschelkalk of the Iberian Range is herein described. The best-preserved trace fossils occur in a dolomicritic bed Ladinian in age, and are represented by small forms with a subcircular, slightly lobed outline and very little penetration depth. They were deposited in a very shallow, quiet-water environment with transition to supratidal/emerged areas. The low diversity of both trace fossils and skeletal remains point to stressful conditions related to strong salinity variations and/or poor water circulation. A comparison was made with Zoophycos from Anisian deposits of the Muschelkalk in Germany. This showed that both forms are quite simple and penetrate only the shallowest tiers, although they are different in whorl outline and lobe shape. This confirms that, notwithstanding the morphological variability of this group, Zoophycos still maintained a quite simple structure in the Triassic. A shallow-water environment was deduced for both localities, confirming that at least until the Early Jurassic Zoophycos had not definitively migrated toward deep-water areas.     

Les pistes dinosauroïdes du Trias moyen français : interprétation et réévaluation de la nomenclature

Numerous dinosauroid footprints which showing sometimes manus imprint mark were gathered, since 1960, from the lower sandstones Triassic formations of the eastern border of the Massif Central (France). Tracks bearing levels are dated from palynological, micropalaeontological and palichnological data. They belong to the period upper Anisian-lower Ladinian. The paleontological results show bipedal digitigrade reptiles with erected, long hind limbs, having also pentadactyl mani and (II-IV) tridactyl feet. The osteological feet inferred structure is like that of Ceratosauria of Late Triassic age. The skeletons of first Dinosauria, diversified already well, are known in summit Ladinian and lower Carnien and those of their ancestors, Dinosauriformes, in Ladinian. And, for this reason, the aniso-ladinian dinosauroid footprints are ascribed to these last animals which thus appeared earlier, to Anisan even to late Olenekian. The chirotheroid hands show a “pseudosuchian” origin which possibly took place during the late Olenekian; feet modifications of these Crurotarsi being characterized by I and V digits reduction and a meso-tarsal joint. The Anisian-Ladinian dinosauroid footprints are ascribed to the ichnospecies Coelurosaurichnus perriauxi and Anchisauripus bibractensis. The discriminant analysis computed from these latter ichnospecies, and others from the German Triassic, French and USA Hettangian indicate that C. perriauxi and A. bibractensis can not be included into Grallator sensu Lull, 1953 or Coelurosaurichnus of Franconie. By this way, these taxa are well original and till now, there was no reason to change their nomenclature. Nevertheless because the numerous changes of Grallator which gathers now, most of dinosauroid footprints, it could be possible to include them into Grallator for the feet and into Atreipus when the manus trace is connected with the foot.     

The origin and early evolution of dinosaurs

The oldest unequivocal records of Dinosauria were unearthed from Late Triassic rocks (approximately 230 Ma) accumulated over extensional rift basins in southwestern Pangea. The better known of these are Herrerasaurus ischigualastensis, Pisanosaurus mertii, Eoraptor lunensis, and Panphagia protos from the Ischigualasto Formation, Argentina, and Staurikosaurus pricei and Saturnalia tupiniquim from the Santa Maria Formation, Brazil. No uncontroversial dinosaur body fossils are known from older strata, but the Middle Triassic origin of the lineage may be inferred from both the footprint record and its sister‐group relation to Ladinian basal dinosauromorphs. These include the typical Marasuchus lilloensis, more basal forms such as Lagerpeton and Dromomeron, as well as silesaurids: a possibly monophyletic group composed of Mid‐Late Triassic forms that may represent immediate sister taxa to dinosaurs. The first phylogenetic definition to fit the current understanding of Dinosauria as a node‐based taxon solely composed of mutually exclusive Saurischia and Ornithischia was given as “all descendants of the most recent common ancestor of birds and Triceratops”. Recent cladistic analyses of early dinosaurs agree that Pisanosaurus mertii is a basal ornithischian; that Herrerasaurus ischigualastensis and Staurikosaurus pricei belong in a monophyletic Herrerasauridae; that herrerasaurids, Eoraptor lunensis, and Guaibasaurus candelariensis are saurischians; that Saurischia includes two main groups, Sauropodomorpha and Theropoda; and that Saturnalia tupiniquim is a basal member of the sauropodomorph lineage. On the contrary, several aspects of basal dinosaur phylogeny remain controversial, including the position of herrerasaurids, E. lunensis, and G. candelariensis as basal theropods or basal saurischians, and the affinity and/or validity of more fragmentary taxa such as Agnosphitys cromhallensis, Alwalkeria maleriensis, Chindesaurus bryansmalli, Saltopus elginensis, and Spondylosoma absconditum. The identification of dinosaur apomorphies is jeopardized by the incompleteness of skeletal remains attributed to most basal dinosauromorphs, the skulls and forelimbs of which are particularly poorly known. Nonetheless, Dinosauria can be diagnosed by a suite of derived traits, most of which are related to the anatomy of the pelvic girdle and limb. Some of these are connected to the acquisition of a fully erect bipedal gait, which has been traditionally suggested to represent a key adaptation that allowed, or even promoted, dinosaur radiation during Late Triassic times. Yet, contrary to the classical “competitive” models, dinosaurs did not gradually replace other terrestrial tetrapods over the Late Triassic. In fact, the radiation of the group comprises at least three landmark moments, separated by controversial (Carnian‐Norian, Triassic‐Jurassic) extinction events. These are mainly characterized by early diversification in Carnian times, a Norian increase in diversity and (especially) abundance, and the occupation of new niches from the Early Jurassic onwards. Dinosaurs arose from fully bipedal ancestors, the diet of which may have been carnivorous or omnivorous. Whereas the oldest dinosaurs were geographically restricted to south Pangea, including rare ornithischians and more abundant basal members of the saurischian lineage, the group achieved a nearly global distribution by the latest Triassic, especially with the radiation of saurischian groups such as “prosauropods” and coelophysoids.     

Geological significance of the discovery of Middle Triassic (Ladinian) radiolarians from the Hong Hoi Formation of the Lampang Group,Sukhothai Zone,northern Thailand

This paper presents a newly found fauna of Ladinian (Middle Triassic) radiolarians from the Hong Hoi Formation of the Lampang Group, Sukhothai Zone, northern Thailand. The Ladinian age determined by the radiolarian fauna concords with the age previously determined by mollusks. The study section consists of intercalated sandstone and shale in the lower part and a thick conglomerate in the upper part. The radiolarian-bearing siliceous beds are intercalated within the lower unit. The lithic sandstone of the lower unit consists mainly of volcanic rock fragments, quartz, and feldspar, whereas the thickly bedded conglomerate of the upper unit is characterized by abundant gravel-sized clasts of volcanic rock and limestone. These lithic features of the study section suggest that during deposition the Hong Hoi Formation was located near a supply of volcanic materials. A forearc basin close to the Sukhothai Arc would be the most suitable environment for the deposition. The Ladinian age determined by the radiolarian fauna supports the occurrence of intensive volcanic activity within the Sukhothai Arc during the Middle Triassic.