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Stratigraphy, paleontology, and depositional setting of the Late Eocene (Priabonian) lower Pagat Member, Tanjung Formation, in the Asem Asem Basin, South Kalimantan, Indonesia
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Marine sedimentary rocks of the late Eocene Pagat Member of the Tanjung Formation in the Asem Asem Basin near Satui, Kalimantan, provide an important geological archive for understanding the paleontological evolution of southern Kalimantan (Indonesian Borneo) in the interval leading up the development of the Central Indo-Pacific marine biodiversity hotspot. In this paper, we describe amoderately diverse assemblage of marine invertebrates within a sedimentological and stratigraphical context. In the studied section, the Pagat Member of the Tanjung Formation records an interval of overall marine transgression and chronicles a transition from the marginal marine and continental siliciclastic succession in the underlying Tambak Member to the carbonate platform succession in the overlying Berai Formation. The lower part of the Pagat Member contains heterolithic interbedded siliciclastic sandstone and glauconitic shale, with thin bioclastic floatstone and bioclastic rudstone beds. This segues into a calcareous shale succession with common foraminiferal packstone/rudstone lenses interpreted as low-relief biostromes. A diverse trace fossil assemblage occurs primarily in a muddy/glauconitic sandstone, sandy mudstone, and bioclastic packstone/rudstone succession, constraining the depositional setting to a mid-ramp/mid to distal continental shelf setting below fair-weather wave base but above stormwave base. Each biostrome rests upon a storm-generated ravinement surface characterized by a low-diversity Glossifungites or Trypanites trace fossil assemblage. The erosional surfaces were colonized by organisms that preferred stable substrates, including larger benthic foraminifera, solitary corals, oysters, and serpulid annelid worms. The biostromes comprised islands of highmarine biodiversity on the mud-dominated Pagat coastline. Together, the biostromes analyzed in this study contained 13 genera of symbiont-bearing larger benthic foraminifera, ∼40 mollusk taxa, at least 5 brachyuran decapod genera, and 6 coral genera (Anthemiphyllia, Balanophyllia, Caryophyllia, Cycloseris, Trachyphyllia, and Trochocyathus), as well as a variety of bryozoans, serpulids, echinoids, and asterozoans. High foraminiferal and molluscan diversity, coupled with modest coral diversity, supports the hypothesis that the origin of the diverse tropical invertebrate faunas that characterize the modern Indo-Australian region may have occurred in the latest Eocene/earliest Oligocene.
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RBINS Staff Publications 2025 OA
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Depositional framework of the Sangkarewang and Sawahlunto Formations, Ombilin Basin, West Sumatra, Indonesia
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Analyses of rock samples collected during recent fieldwork in the Ombilin Basin of west-central Sumatra, Indonesia yielded pollen data that constrain the age and depositional setting of associated plant macrofossil and vertebrate fossil-bearing units in the Sangkarewang and Sawahlunto formations. Articulated fish and plant fossils were recovered from bedding plane surfaces of fissile, laminated shales in the Sangkarewang Formation that are interpreted to have been deposited in an actively-subsiding, deep, anoxic lake. The overlying Talawi Member of the Sawahlunto Formation records stratigraphy consistent with deposition in a segue to marginal lacustrine marsh and poorly-drained paleosol settings. Interbedded carbonate mudstone / wackestone and lignitic claystone units in the basal Talawi Member preserve scattered, disarticulated fossils of fish, reptiles, an amphibian, and one mammal tooth. These beds grade into a heterolithic succession of fine-grained clastic rock, with coal interbeds likely deposited in a coastal alluvial setting. Marine influences in this interval are indicated by the nature of physical sedimentary structures in several zones, the presence of trace fossils such as Diplocraterion, Cylindrichnus and Teichichnus, and the occurrence of foraminiferal linings, dinocysts and other palynomorphs indicative of mangrove and back-mangrove settings. Palynological analysis indicates that the most probable age of the Sawahlunto Formation ranges from the middle to late Eocene, with a possible extension from the middle Eocene to the early Oligocene.
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RBINS Staff Publications 2025 OA
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First crocodyliform fossils from the Eocene of Indonesia
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The Paleogene crocodyliform record is rich in taxonomic diversity, preserving crown and stemeusuchians alongside late-surviving neosuchians and notosuchians. This richness is mainly known from the extratropical latitudes of the New World and Eurasia, contrasting a poorly sampled tropical record. Within the tropics, the Paleogene of low-latitude southeast Asia is comparatively undersampled, with the Eocene Krabi Formation of Thailand representing the southernmost fauna. This crocodyliform fauna is composed of orientalosuchins and gavialoids, consistent with more northern records from southern Asia. Here we describe the first crocodyliform fossils from the Eocene of Indonesia, collected from the middle-late Eocene Talawi Member of the Sawahlunto Formation, west Sumatra. The Talawi Member represents a coastal swamp environment, preserving invertebrates, fish, and turtles along with rare frog, snake, and mammal fossils. Recovered crocodyliform fossils are often isolated and disarticulated, consisting of cranial remains including a partial braincase and jaw fragments, as well as relatively abundant teeth and osteoderms, vertebrae, and at least two autopodial elements. Procoelous vertebrae indicate eusuchian affinities. Osteoderms are diverse, with keeled and keelless squared and subrectangular forms. High and low-crowned fluted tooth morphotypes compare favorably to coeval gavialoids and orientalosuchins. A ziphodont form is present, potentially a planocraniid or sebecosuchian. External morphology of the braincase, such as narrow basioccipital tubera, a basioccipital plate bearing a crest, and a large basisphenoid exposure suggest a non-gavialoid identity. This is supported by preliminary observations of highresolution microCT scans, which imply a lateral carotid foramen ventral to the metotic foramen and laterally aligned medial and lateral eustachian foramina. The Sawahlunto fauna extends the southernmost geographical range of the Eocene southeast Asian crocodyliform fauna and represents the first multitaxon crocodyliform fauna from equatorial Asia. The ziphodont teeth either represent the last-occurring Asian planocraniids in a tropical refugium, or an incursion of Gondwanan sebecosuchians from India into the Asian tropics.
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RBINS Staff Publications 2025 OA
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Recent data on the enigmatic family Raoellidae: how aquatic…how cetacean?
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At the beginning of the 21st century, the discovery of an involucrum on the auditory bulla of Indohyus, a small raoellid artiodactyl from the Indian subcontinent, triggered the phylogenetic gathering of Raoellidae with the Cetacea clade, making them pivotal in addressing questions surrounding the land-to-water transition in Artiodactyla. Micro CT scan investigations and newly collected material from the Kalakot area (Jammu and Kashmir, India), recently greatly increased our knowledge of the cranial and dental features of this group. Here we present new data on cranial morphology of Raoellidae deriving from micro CT scan investigations of Indohyus indirae and Khirtharia inflata. This new body of data comprises investigations of the endocast of the braincase, the complete middle ear including the ossicles and auditory bulla, the petrosal bone, and the cast of the bony labyrinth. It also includes the reconstruction of the complete anterior dentition. This study gives us a comprehensive picture of the features of the Raoellidae head and improves our understanding of their semiaquatic habits. This increased knowledge of raoellids further extends the list of features they share with the first archeocetes, calling into question the definition of the clade Cetacea.
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RBINS Staff Publications 2025 OA
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Revision of the longirostrine crocodilian Thoracosaurus isorhynchus from the Maastrichtian–Danian of northwestern Europe
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“Thoracosaurs” are a group of longirostrine eusuchians known from Upper Cretaceous–lower Paleogene coastal deposits of Europe and North America. Their phylogenetic position is highly debated and varies from one study to the next, ranging from inclusion within Gavialoidea—implying ghost lineages of up to 100 million years—to exclusion from Crocodylia altogether. Despite these issues, many “thoracosaur” taxa have been understudied, suffering from incomplete or outdated descriptions and questionable taxonomic assignment. We present a comprehensive revision of Thoracosaurus isorhynchus, the most common European “thoracosaur.” Here, we redescribe the lectotype and paralectotypes of the species from the Maastrichtian of Mont-Aimé, France, and a skull from the Maastricht type area, The Netherlands. We also add new, previously undescribed cranial and extensive postcranial material from Mont-Aimé. Moreover, comparison with the type material of Thoracosaurus “scanicus” of the Danian of southern Sweden indicates that the latter is a junior synonym of T. isorhynchus, confirming the persistence of this species across the Cretaceous–Paleogene boundary. An array of phylogenetic analyses points to a close relationship between T. isorhynchus and the Cenomanian Portugalosuchus azenhae. This implicates an early emergence of “thoracosaurs” within Gavialoidea, highlighting the stratigraphic inconsistency of this group and a need for up to date descriptions of species belonging to this group.
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RBINS Staff Publications 2025 OA
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Bioerosional marks in the shells of two sea turtle taxa from the middle Eocene of Belgium
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This study analyses the diverse types of bioerosion marks on the shells of two sea turtle specimens from the Lutetian (middle Eocene) of Belgium. The objective is to understand the physical stressors affecting these organisms in ancient marine environments and to identify the potential factors responsible for these changes. The first specimen, the holotype of Eochelone brabantica, presents multiple erosive anomalies on its costal plates. The second individual, corresponding to Puppigerus camperi, exhibits different types of shell deviations, also of an erosive character. The combination of macroscopic and imaging techniques (i.e., CT scanning and 3D surface scanning) allow us the precise observation and identification of the different alterations. Comparative analyses suggest several external factors as potential causes of the anomalies of the two specimens (i.e., invertebrate feeding traces and trauma). This detailed examination provides specific insights into the types and causes of shell alterations in these Eocene turtles, offering a clearer understanding of their interactions in the marine ecosystem in which they lived.
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RBINS Staff Publications 2025 OA
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Morphological study of the anterior dentition in Raoellidae (Mammalia, Artiodactyla), new insight on their dietary habits
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Raoellidae are small artiodactyls from the Indian subcontinent closely related to stem cetaceans. They bring crucial information to understand the early phase of the land-to- water transition in Cetacea. If they are considered to be partly aquatic, the question of their dietary habits remains partly understood due to their “transitional” morphology. Raoellidae are largely documented by their cheek teeth and getting a better knowledge of their anterior dentition constitutes an additional proxy to discuss their feeding habits. In this work, we document the anterior dentition of Indohyus indirae from an unprecedented sample of in situ and isolated teeth from the locality of East Aiji-2 in the Kalakot area (Rajouri district, India). We propose identification criteria for upper and lower incisors and canines in raoellids. Based on CT scan data, virtual reconstruction of in situ dentition, and identification of the isolated incisors and canines, we reconstruct a composite anterior dentition of Indohyus supported by the correspondence of wear facets between upper and lower teeth. This constitutes the first attempt at reconstruction of the anterior dentition of a raoellid. We show that the upper incisors are caniniform and very similar morphologically, whereas the lower incisors are pointed but remain incisiform and quite different from one another. We also describe noticeable intraspecific variation, at the level of upper canines, suggesting a potential sexual dimorphism in this species. Upper and lower incisors are recurved, with the upper incisor row arranged on a widely opened arch. Taken altogether the anterior dentition forms a grasping device, allowing the animal to capture and secure food, a characteristic shared with stem cetaceans. This would mark the first step towards the carnivorous diet in these peculiar artiodactyls.
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RBINS Staff Publications 2025 OA
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Early Delphinida (Cetacea, Odontoceti) from the Miocene of the southern North Sea Basin
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RBINS Staff Publications 2026
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Understanding extreme-wave hazards on high-energy coasts requires a standardised approach to field data collection: Analysis and recommendations.
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Coastal boulder deposits provide vital information on extreme wave events. They are crucial for understanding storm and tsunami impacts on rocky coasts, and for understanding long-term hazard histories. But study of these deposits is still a young field, and growth in investigation has been rapid, without much contact between research groups. Therefore, inconsistencies in field data collection among different studies hinder cross-site comparisons and limit the applicability of findings across disciplines. This paper analyses field methodologies for coastal boulder deposit measurement based using an integrated database (ISROC-DB), and demonstrates inconsistencies in current approaches. We use the analysis as a basis for outlining protocols to improve data comparability and utility for geoscientists, engineers, and coastal planners. Using standardised and comprehensive data reporting with due attention to precision and reproducibility – including site characteristics, boulder dimensions, complete positional data, tide characteristics, and geodetic and local topographic datum information – will help ensure complete data retrieval in the field. Applying these approaches will further ensure that data collected at different times and/or locations, and by different groups, is useful not just for the study being undertaken, but for other researchers to analyse and reuse. We hope to foster development of the large, internally consistent datasets that are the basis for fruitful meta-analysis. This is particularly important given increasing focus on long-term monitoring of coastal change. By recommending a common set of measurements, adaptable to available equipment and personnel, this work aims to support accurate and thorough coastal boulder deposit documentation, enabling broader applicability and future-proofed datasets. Field protocols described and recommended here also apply as best practices for coastal geomorphology field work in general.
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RBINS Staff Publications 2025
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Paleoparasitological analysis of a 15th–16th c. CE latrine from the merchant quarter of Bruges, Belgium: Evidence for local and exotic parasite infections
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RBINS Staff Publications 2025
