The upper part of the Kortrijk Clay Formation (the Roubaix Clay and Aalbeke Clay Members of mid-Ypresian age) has been exposed in road and canal cuttings and clay quarries in the Kortrijk area (western Belgium), and penetrated by several cored boreholes. It is overlain disconformably by the Mont-Panisel Sand Member of the Hyon Sand Formation (upper middle Ypresian). The Roubaix Clay Member contains diverse and well-preserved calcareous nannofossils, dinoflagellate cysts, foraminifera, ostracods and other calcitic microfossils, and less well-preserved mollusc assemblages, while the Aalbeke Clay Member is secondarily decalcified. The calcareous nannofossil subdivision of upper NP11 and lower NP12 has been recognised in the Kortrijk area, and calibrated with the NW European mid-Ypresian dinoflagellate cyst, ostracod and planktonic foraminiferal zones and datums (e.g. Subbotina influx). Several medium-scale depositional sequences, with an estimated duration of 400 kyr or less, have been recorded. Their respective boundaries coincide with the resistivity maxima identified on the majority of the wireline log profiles of the Belgian Ypresian. Integrated biostratigraphic, magnetostratigraphic and sequence stratigraphic analysis enables correlation with other areas in Belgium, with the London Clay Formation of southern England, and with the standard chronostratigraphic scale. A marine erosion surface has been identified at the base of Unit 20 in the Kortrijk area (mid-Ypresian, early Biochron NP12, middle C24n.1n, ~ 52.8 Ma), corresponding to the first occurrence of estuarine channel-fill units in southern England. This indicates a brief but profound sea-level fall, either eustatically or tectonically controlled. The composite Kortrijk section is proposed as a reference section for the middle Ypresian in the southern North Sea Basin, and for similar settings in mid- to high-latitudes of the Northern Hemisphere (e.g. Kazakhstan and Crimea).
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RBINS Staff Publications 2017
Among the extant crocodylians are two species with long, narrow snouts: Gavialis gangeticus,the Indian gharial and Tomistoma schlegelii, the "false" gharial. These enigmatic species are considered by the IUCN red list as critically endangered and vulnerable, respectively. However, despite this, knowledge of their evolutionary history is lacking. Extensive debate has surrounded the gharials for over four decades and remains unsolved today: the so-called gharial problem. Whereas molecular studies consistently indicate that these two species are sister taxa, morphological studies of both living and fossil taxa find that they belong to distantly related lineages. Moreover, molecular clock estimates indicate a shallow divergence time of 18-31 million years ago. This entirely contradicts the rich fossil record of gharials: in contrast to the modern gharials, these fossil taxa comprise a huge diversity and suggest that tomistomines and gavialines have diverged from each other at least 70 million years ago, prior to the K/Pg mass extinction. European museums, and especially the Royal Belgian Institute of Natural Sciences, Brussels, comprise rich collections containing many of the oldest fossil gavialoids, crucial to solving the gharial problem. Nevertheless, few modern morphological studies have been performed on these specimens, and their stratigraphic age is often poorly constrained. Therefore, in a new project we will use a multidisciplinary approach to study these specimens, combining morphological study and biostratigraphic analyses using dinoflagellate cysts. Moreover, we will revise the classical methods used by paleontologists to study fossil crocodylians, devising a new phylogenetic framework that makes use of both morphological, molecular, and biostratigraphic data. Here, we will present some of the first preliminary results of this project.
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RBINS Staff Publications 2023
Caecilians are elongate, limbless and annulated amphibians that, with the exception of one aquatic family, all have an at least partly fossorial lifestyle. It has been suggested that caecilian evolution resulted in sturdy and compact skulls with fused bones and tight sutures, as an adaptation to their head-first burrowing habits. However, although their cranial osteology is well described, relationships between form and function remain poorly understood. In the present study, we explored the relationship between cranial shape and in vivo burrowing forces. Using micro-computed tomography (µCT) data, we performed 3D geometric morphometrics to explore whether cranial and mandibular shapes reflected patterns that might be associated with maximal push forces. The results highlight important differences in maximal push forces, with the aquatic Typhlonectes producing a lower force for a given size compared with other species. Despite substantial differences in head morphology across species, no relationship between overall skull shape and push force could be detected. Although a strong phylogenetic signal may partly obscure the results, our conclusions confirm previous studies using biomechanical models and suggest that differences in the degree of fossoriality do not appear to be driving the evolution of head shape.
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RBINS Staff Publications 2021
