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Deciphering the influence of evolutionary legacy and functional constraints on the patella: an example in modern rhinoceroses amongst perissodactyls
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In mammals, the patella is the biggest sesamoid bone of the skeleton and is of crucial importance in posture and locomotion, ensuring the role of a pulley for leg extensors while protecting and stabilizing the knee joint. Despite its central biomechanical role, the relation between the shape of the patella and functional factors, such as body mass or locomotor habit, in the light of evolutionary legacy are poorly known. Here, we propose a morphofunctional investigation of the shape variation of the patella among modern rhinoceroses and more generally among perissodactyls, this order of ungulates displaying a broad range of body plan, body mass and locomotor habits, to understand how the shape of this sesamoid bone varies between species and relatively to these functional factors. Our investigation, relying on three dimensional geometric morphometrics and comparative analyses, reveals that, within Rhinocerotidae and between the three perissodactyl families, the shape of the patella strongly follows the phylogenetic affinities rather than variations in body mass. The patellar shape is more conservative than initially expected both within and between rhinoceroses, equids and tapirs. The development of a medial angle, engendering a strong mediolateral asymmetry of the patella, appears convergent in rhinoceroses and equids, while tapirs retain a symmetric bone close to the plesiomorphic condition of the order. This asymmetric patella is likely associated with the presence of a “knee locking” mechanism in both equids and rhinos. The emergence of this condition may be related to a shared locomotor habit (transverse gallop) in both groups. Our investigation underlines unexcepted evolutionary constraints on the shape of a sesamoid bone usually considered as mostly driven by functional factors.
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RBINS Staff Publications 2024 OA
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Inferring internal anatomy from the trilobite exoskeleton: the relationship between frontal auxiliary impressions and the digestive system
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The digestive system of trilobites is rarely preserved. As a result, many aspects of its organization remain unknown. Fortunately, the exoskeleton sometimes preserves evidence of soft-tissue attachment sites that can be used to infer internal anatomy. Among them are the frontal auxiliary impressions (FAIs), probable soft-tissue insertion sites located on the fronto-median glabellar lobe of some trilobites. FAIs are herein described in the Carboniferous trilobite Phillipsia belgicaOsmólska 1970– representing the only known example of such structures in the Proetida and their youngest occurrence. A taphonomic scenario is proposed to explain their variable preservation. Although particularly common in the Phacopina, FAIs or FAI-like structures are also found in several orders that differ greatly. Comparisons with modern analogues suggest that FAIs might represent attachment sites for extrinsic muscles associated with a differentiated crop within the foregut. A review of purported remains of the trilobite digestive system indicates that it usually consisted of a tube-like tract flanked by a variable number of metamerically paired diverticulae. Its anterior portion is not particularly individualized, except in a few specimens that might hint at the presence of a crop. This differentiation of a crop might have constituted a secondarily evolution of the foregut in trilobites, occurring independently in different clades. Accompanied by a strengthening of associated extrinsic muscles, this modification of the foregut might explain the presence of more conspicuous muscle insertion sites on the glabella. Study of FAIs might therefore provide new data on the anatomy of the foregut in trilobites and evidence of diverse feeding habits.
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A new Placoderm fish (Acanthothoraci) from the Early Devonian Jauf Formation (Saudi Arabia)
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An exceptionally well-preserved new acanthothoracid (placoderm fish) presenting complete endocranium and skull roof, from Saudi Arabia (Qasr Limestone Member, Jauf Formation), Early Devonian in age, is described as Arabosteus variabilis n. gen., n. sp. Compared to other Acanthothoraci, the new taxon exhibits a skull roof variable in its dermal plate distribution (e.g., a supernumerary plate: the posterior central plate) and sensory line pattern. Even the different specimens of this taxon show such variability between them. Arabosteus variabilis n. gen., n. sp. enlarges the scope of our knowledge of Acanthothoraci and Placodermi in general. Traditionally, the Arthrodira, one of the historically earliest described groups, provide the standard reference model for the placoderm skull roof pattern. The interpretation of the acanthothoracid skull roof pattern of the Saudi taxon from an arthrodiran model and the establishment of homologies is impossible to resolve unless based on prior assumptions (e.g., hypothesis of fragmentation or fusion for the paranuchal plate complex). The lateral line system of A. variabilis n. gen., n. sp. is unstable (e.g., presence or absence of the postmarginal sensory line canal) making it ambiguous to define bone homology and terminology. Consequently spatial distribution of skull roof plates has been retained for such a task with a minimal reference to the instable features of the sensory line groove distribution.
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Vertebrate predation in the Late Devonian evidenced by bite traces and regurgitations: implications for an early tetrapod freshwater ecosystem.
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The terrestrialization process by vertebrates occurred during the Devonian period, with fully land-dwelling tetrapods recorded in the Carboniferous. Thus, the Late Devonian is an important period for deciphering the ecological pressures that applied during the water-to-land transition. Higher predation pressures in the underwater environment have been suggested as an influential biotic evolutionary factor in this key habitat shift. Direct evidence of ancient predation on Palaeozoic vertebrates is seen in the form of rare traces preserved on fossils, and these range from trauma observed on the skeleton (such as attack marks) to ingested food remains (bromalites). The late Famennian freshwater ecosystem of Strud (Belgium) consists of a rich assemblage of many coeval gnathostomes or jawed fishes (placoderms, ‘acanthodians’, actinopterygians, and various sarcopterygian groups including tetrapods). Here we analyse the record of direct evidence for predation in the Strud vertebrate fossil assemblage. We recognize 12 regurgitalites and 13 bite traces, including a rare case of a tooth embedded in its original prey body target. Fossils from regurgitalites were imaged using scanning electron microscopy and chemically analysed to test for their possible ingestion signature by comparison with other isolated skeletal remains from the same locality. From this evidence, tristichopterid tetrapodomorphs are inferred to be the highest consumers of the trophic network, targeting small placoderms, and porolepiforms, and probably congeners. We observe two possible prey patterns in regurgitalites, for sarcopterygians and actinopterygians, both of which are associated with acanthodians. In Strud, no trophic position can be deduced for tetrapods from direct fossil evidence of predation.
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RBINS Staff Publications 2022
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Developmental types and a new cryptic species of Chicoreus (Gastropoda: Muricidae) from Papua New Guinea
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RBINS Staff Publications 2025
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A new bird-like dinosaur from the Upper Cretaceous of Mongolia with extremely robust hands supports niche partitioning among velociraptorines
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RBINS Staff Publications 2025 OA
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Analysis of Iguanodon bernissartensis teeth and bones using in-situ trace element, oxygen and strontium isotope composition: Implication for paleoecology, paleoenvironment and diagenesis
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RBINS Staff Publications 2025 OA
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Deciphering causes and behaviors: A recurrent pattern of tail injuries in hadrosaurid dinosaurs
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RBINS Staff Publications 2025
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Cariocecus bocagei, a new basal hadrosauroid from the Lower Cretaceous of Portugal
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RBINS Staff Publications 2025
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Multituberculate mammal of possible North American affinity in the Maastrichtian of the Russian Far East
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RBINS Staff Publications 2025 OA
