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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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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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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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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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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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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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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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Hydro-meteorological influences and multimodal suspended particle size distributions in the Belgian nearshore area (southern North Sea)
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Suspended particulate matter (SPM) concentration and particle size distribution (PSD) were assessed in a coastal turbidity maximum area (southern North Sea) during a composite period of 37 days in January–April 2008. PSDs were measured with a LISST 100X and classified using entropy analysis in terms of subtidal alongshore flow. The PSDs during tide-dominated conditions showed distinct multimodal behaviour due to flocculation, revealing that the building blocks of flocs consist of primary particles (<3 μm) and flocculi (15 μm). Flocculi comprise clusters of clay minerals, whereas primary particles have various compositions (calcite, clays). The PSDs during storms with a NE-directed alongshore subtidal current (NE storms) are typically unimodal and characterised by mainly granular material (silt, sand) resuspended from the seabed. During storms with a SW-directed alongshore subtidal current (SW storms), by contrast, mainly flocculated material can be identified in the PSDs. The findings emphasise the importance of wind-induced advection, alongshore subtidal flow and highly concentrated mud suspensions (HCMSs) as regulating mechanisms of SPM concentration, as well as other SPM characteristics (cohesiveness or composition of mixed sediment particles) and size distribution in a high-turbidity area. The direction of subtidal alongshore flow during SW storm events results in an increase in cohesive SPM concentration, HCMS formation, and the armouring of sand; by contrast, there is a decrease in cohesive SPM concentration, no HCMS formation, and an increase in sand and silt in suspension during NE storms.
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RBINS Staff Publications 2017
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Multimodality of a particle size distribution of cohesive suspended particulate matters in a coastal zone
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Particle size distributions (PSDs) of suspended particulate matters in a coastal zone are lognormal and multimodal in general. The multimodal PSD, which is caused by the mixing of multiple particle and aggregate size groups under flocculation and erosion/resuspension, is a record of the particle and aggregate dynamics in a coastal zone. Curve-fitting software was used to decompose the multimodal PSD into subordinate lognormal PSDs of primary particles, flocculi, microflocs, and macroflocs. The curve-fitting analysis for a time series of multimodal PSDs in the Belgian coastal zone showed the dependency of the multimodality on (1) shear-dependent flocculation in a flood and ebb tide, (2) breakage-resistant flocculation in the spring season, and (3) silt-sized particle erosion and advection in a storm surge. Also, for modeling and simulation purposes, the curve-fitting analysis and the settling flux estimation for the multimodal PSDs showed the possibility of using discrete groups of primary particles, flocculi, microflocs, and macroflocs as an approximation of a continuous multimodal PSD.
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Competition between kaolinite flocculation and stabilization in divalent cation solutions dosed with anionic polyacrylamides
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Divalent cations have been reported to develop bridges between anionic polyelectrolytes and negatively-charged colloidal particles, thereby enhancing particle flocculation. However, results from this study of kaolinite suspensions dosed with various anionic polyacrylamides (PAMs) reveal that Ca2+ and Mg2+ can lead to colloid stabilization under some conditions. To explain the opposite but coexisting processes of flocculation and stabilization with divalent cations, a conceptual flocculation model with (1) particle-binding divalent cationic bridges between PAM molecules and kaolinite particles and (2) polymer-binding divalent cationic bridges between PAM molecules is proposed. The particle-binding bridges enhanced flocculation and aggregated kaolinite particles in large, easily-settleable flocs whereas the polymer-binding bridges increased steric stabilization by developing polymer layers covering the kaolinite surface. Both the particle-binding and polymer-binding divalent cationic bridges coexist in anionic PAM- and kaolinite-containing suspensions and thus induce the counteracting processes of particle flocculation and stabilization. Therefore, anionic polyelectrolytes in divalent cation-enriched aqueous solutions can sometimes lead to the stabilization of colloidal particles due to the polymer-binding divalent cationic bridges.
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RBINS Staff Publications
