Jesse James Hennekam

Proboscideans exhibit limb morphologies specialised for supporting extreme body masses under predominantly compressive loading. These graviportal adaptations include repositioning of the limb bones closer to the trunk, resulting in a columnar stance. Among proboscideans, two humeral morphotypes have been proposed (slender and robust), yet their functional significance under compressive loading remains poorly understood. Finite element analysis (FEA) is applied to evaluate biomechanical performances of proboscidean humeri subject to axial compression, simulating conditions associated with a columnar stance and deviations from it. Our results reveal clear differences between morphotypes, with slender humeri performing worse than the robust morphotype and functioning optimally under near‐axial loading. Robust humeri consistently exhibit lower peak stress under both neutral and off‐axis loading and show considerable resistance to mediolateral stresses. Across all taxa, stress magnitudes generally increase when deviating from a neutral orientation, especially during posterior loading orientations, highlighting the mechanical importance of maintaining columnar limb posture. These findings support the hypothesis that robust morphologies are better adapted to resist multidirectional stresses, while slender morphologies favour energetic and locomotor efficiency. This study demonstrates the applicability of FEA in assessing compressive performance in postcranial elements and provides a novel framework for investigating biomechanical adaptations in graviportal taxa.

The dormice are a family of small- to medium-sized rodents found across Europe, Asia and Africa. The current extant diversity is represented by 29 species across nine genera (Holden-Musser et al., ...

Insular gigantism is an evolutionary phenomenon whereby small animals become bigger on islands compared to their mainland relatives. The abundance of insular giant taxa in the fossil record suggests the presence of a universal “giant niche” present on islands, with resource limitation as a potential driver for this process. However, insular habitats are ecologically diverse, suggesting that island taxa adopt different survival strategies, including adaptations for foraging behaviours. Here we used finite element analysis to evaluate insular feeding niche adaptations in some of the most extreme examples of insular gigantism: Mediterranean giant dormice. We calculated stress, strain and mechanical advantage during incisor and molar biting for three extinct insular giant species (Leithia melitensis, Hypnomys morpheus, H. onicensis), an extant giant (Eliomys quercinus ophiusae), and their extant non-giant mainland relative, the generalist-feeder Eliomys quercinus. Our results show that dietary adaptations vary between giant taxa on different islands, and can occur relatively rapidly. Furthermore, the functional mandibular morphology in some insular taxa indicate adaptations moving away from a generalist feeding strategy towards greater trophic specialization. We show that the “insular giant niche” varies between islands and across time periods, arguing against a universal ecological driver for insular gigantism in small mammals.

Dormice are widely dispersed across various ecosystems in Eurasia and Africa and among the oldest extant rodent lineages. Despite distinct morphological variation to be present between groups, comprehensive morphometrical studies on the dormouse skull are limited. Here, the form of eight out of the nine extant dormouse genera was analysed using 3D geometric morphometrics and linear biomechanical measurements, providing a better understanding of the overall morphological variation present within Gliridae. Species-, genus- and family-specific morphological trends in both the size and shape of the cranium and mandible are linked with specific habitats and feeding strategies. Smaller dormice show adaptations to a more arboreal lifestyle such as a relatively enlarged braincase and an inferiorly reoriented foramen magnum. Larger dormice show cranial modifications, including clear flattening of the skull and a more posteriorly positioned foramen magnum, hinting towards a more rupicolous lifestyle. Furthermore, specimens inhabiting arid areas appear to have more inflated auditory bullae, whereas other variable features, such as the length of the incisive foramen, were not associated with either size changes or climatic variables. Lastly, more robust and horizontally orientated zygomatic arches as well as increased robusticity of the molar row appear to be linked with herbivory in dormice, whereas thinner arches and small concave molars are seen in more insectivorous species. This study reveals clear convergent adaptations between dormouse species and results in a better understanding of ecological drivers underpinning the morphological divergence present within Gliridae.

Dormice exhibit both inter- and intrageneric variation in cranial and mandibular morphology. Using geometric morphometrics, the form of eight out of nine extant dormouse genera was analysed, to provide a better understanding of the overall morphological variation present within Gliridae. Three genera representing the subfamilies, were studied in more detail. Species-, genus- and family-specific morphological trends are linked with certain habitats and feeding strategies. Smaller dormice show adaptations to a more arboreal lifestyle such as a relatively enlarged braincase and an inferiorly reoriented foramen magnum. Larger dormice show cranial modifications, including clear flattening of the skull and a more posteriorly positioned foramen magnum, hinting towards a more rupicolous lifestyle. Furthermore, specimens inhabiting arid areas appear to have more inflated auditory bullae, whereas other variable features, such as the length of the incisive foramen, were not associated with either size changes nor climatic variables. Lastly, more robust and horizontally orientated zygomatic arches as well as increased robusticity of the molar row appear to be linked with herbivory in dormice, whereas thinner arches and small concave molars are seen in more insectivorous species. This study results in a better understanding of ecological drivers underpinning the morphological divergence present within Gliridae.

Insular gigantism—evolutionary increases in body size from small-bodied mainland ancestors—is a conceptually significant, but poorly studied, evolutionary phenomenon. Gigantism is widespread on Mediterranean islands, particularly among fossil and extant dormice. These include an extant giant population of Eliomys quercinus on Formentera, the giant Balearic genus † Hypnomys and the exceptionally large † Leithia melitensis of Pleistocene Sicily. We quantified patterns of cranial and mandibular shape and their relationships to head size (allometry) among mainland and insular dormouse populations, asking to what extent the morphology of island giants is explained by allometry. We find that gigantism in dormice is not simply an extrapolation of the allometric trajectory of their mainland relatives. Instead, a large portion of their distinctive cranial and mandibular morphology resulted from the population- or species-specific evolutionary shape changes. Our findings suggest that body size increases in insular giant dormice were accompanied by the evolutionary divergence of feeding adaptations. This complements other evidence of ecological divergence in these taxa, which span predominantly faunivorous to herbivorous diets. Our findings suggest that insular gigantism involves context-dependent phenotypic modifications, underscoring the highly distinctive nature of island faunas.