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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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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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3D models related to the publication: Morphological study of the anterior dentition in Raoellidae (Mammalia, Artiodactyla), new insight on their dietary habits
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The present 3D dataset contains 3D models of new material from the middle Eocene of the Upper Subathu Formation in the Kalakot area (India), documenting the anterior dentition of the raoellid Indohyus indirae. Raoellidae are closely related to stem cetaceans and bring crucial information to understand the earliest phase of land to water transition in Cetacea.
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Do diversification and dispersals of early Eocene perissodactyls differ from those of other modern mammals?
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Perissodactyls make their first appearance in the fossil record during the Paleocene-Eocene Thermal Maximum (PETM), 56 Ma ago, at the same time as most modern placental mammal orders. However, their early diversification remains unclear since all main groups (Equidae, Isectolophidae, Ceratomorpha, Ancylopoda and Brontotheriidae) appear at the same time with numerous genera and are already diverse, contrary to other modern mammal orders, which have a much lower diversity. Moreover, several early perissodactyl genera seem endemic to each of the three Holarctic continents, rather than cosmopolitan as is the case for other mammal groups. We investigate the early evolution of perissodactyls by analyzing a new dataset focusing on early species to obtain a new expansive phylogeny. This large-scale phylogeny shows that the number of early perissodactyl genera was over-estimated and supports the synonymy of several genera. In addition, many species that were named as “Hyracotherium” in the past (or sometimes “Eohippus”, the “dawn-horse”) are not actually closely related to horses, including Hyracotherium itself, but can be considered as basal perissodactyls. Among the latter, at least Pliolophus and Cardiolophus experienced vast and fast dispersals between North America, Europe and Asia, during the PETM. This paleobiogeographic scenario much resembles the one of other earliest Eocene mammals, which comprise genera that are often found in at least two continents, such as in artiodactyls, primates, carnivorans, hyaenodontids, hyopsodontids, phenacodontids or rodents. Here, we show that the paleobiogeographic distribution of earliest perissodactyls does not differ from that of other modern mammals.
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Tomography of three articulated perissodactyl skeletons from Messel
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The perissodactyls from the UNESCO World Heritage site of Messel (MP11; around 47 Ma) are among the most well-known fossils from this site, and belong to at least five different genera: three equoids (Propalaeotherium, Eurohippus, and Hallensia) and two tapiromorphs (Lophiodon and Hyrachyus). Here, we investigated by X-ray microtomography at the DTHE (MateIS Laboratory, Lyon) the anatomy of three articulated skeletons from the Royal Belgian Institute of Natural Sciences collection: two specimens of Eurohippus messelensis, as well as the only accessible skeleton of Hallensia matthesi. The segmented 3D models allow us to visualize for the first time some cranial, dental and postcranial features that were previously concealed. Surprisingly, the tooth rows of the two specimens of E. messelensis show two different morphologies. One is typical of E. messelensis whereas the other shows all the diagnostic characters of E. parvulus expressed by Franzen (2006). However, based on the monograph on equoids from Messel by Franzen (2007), E. messelensis was only recognized in Messel, whereas E. parvulus was known from several other localities, notably in the Geiseltal, but not in Messel. We thus suggest that E. parvulus may have also been present in Messel, which raises the question of their potential synonymy. Finally, the preservation of the skeleton of Hallensia matthesi does not permit to observe the fine anatomy of the skeleton, but still permits to discuss important characters such as the number of fingers.
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The biodiversity of the Eocene Messel vertebrates based on the Belgian Collections
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The paleontological collections of the Royal Belgian Institute of Natural Sciences include a beautiful collection of 393 vertebrate specimens from the Messel Pit: 58 fish, 18 amphibians, 79 reptiles, 108 birds and 130 mammals. This collection is the largest Messel collection outside Germany and belongs to the „big four” (Smith et al. 2024). It results from a fieldwork partnership with the Seckenberg Research Institute, Frankfurt between 1982 and 1988, so a few years before the Messel pit was listed in 1995 as UNESCO World Heritage site. With a few exceptions, most of the specimens have been collected by the Belgians. However, most of the specimens have been prepared by German preparators. Here we show the Messel biodiversity based on the Brussels collection. The collection is relatively well diversified and contains 24 type and figured specimens. Among them are remarkable specimens such as the holotype of the hyaenodont carnivorous mammal Lesmesodon edingeri, the paratypes of the trogon bird Masillatrogon pumilio and embalonurid bat Tachypteron franzeni, the exquisitely 3-D prepared turtle lovers Allaeochelys crassesculpta and armored crocodylia Diplocynodon deponiae, and the only skeleton of the basal perissodactyl Hallensia matthesi housed in a public collection. The archives related to this collection are currently being digitized and several new studies are now based on micro-CT scan technology allowing to „discover” hidden characters.
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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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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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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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India as a “Noah’s Ark” before Collision with Eurasia: Palaeoenvironment and Palaeobiogeography of the Continental Early Eocene Vertebrate Fauna of Gujarat
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For the past twenty years, an Indian-American-Belgian team carried out twelve seasons of collaborative fieldwork in search of vertebrates from the Cambay Formation in lignite mines of Gujarat, western India. Here is a summary of our main discoveries in the Vastan, Mangrol, and Tadkeshwar mines, including an updated overview of the whole vertebrate fauna. The fauna is around 54.5 million years old, representing tropical rainforest conditions in a coastal brackish palaeoenvironment. It includes the earliest modern mammals from the Indian subcontinent as well as endemic taxa. The most important result at the palaeobiogeographical level is the discovery of several vertebrate taxa of Gondwanan affinities, indicating that the early Eocene was a crucial period in India when Laurasian taxa with western European affinities co-existed with relict taxa from Gondwana before the actual collision of India and Eurasia. Terrestrial faunas could have dispersed to or from Europe when the Indian subcontinent came into contact, episodically, with different island blocks, such as the Kohistan-Ladakh island-arc system, along the northern margin of Neotethys Ocean.
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