The dormice (Gliridae) represent a relatively small family of rodents, but exhibit considerable 21 variation in their cranial anatomy. The skull morphology of almost all genera of dormice was 22 described from osteological specimens by Wahlert et al. (1993). However, the rare desert 23 dormouse, Selevinia betpakdalaensis, was only assessed using previous descriptions and 24 photographic images, resulting in difficulties with assigning all cranial features within this 25 particular genus. In this study, the crania and mandibles of two adult individuals of this genus 26 were scanned using micro-computed tomography and virtually reconstructed. From these 27 reconstructions, we describe in detail the highly unusual cranial and mandibular morphology 28 of the desert dormouse and determine the states of the cranial and mandibular characters 29 described by Wahlert et al. (1993). These morphological characters were used to compare this 30 species with previously described dormouse genera, showing a clear resemblance between 31 Selevinia and the small mouse-tailed dormouse genus Myomimus. Derived morphological 32 features unique to Selevinia indicate clear adaptations to a desert-like environment, as well as 33 hinting towards an insectivorous diet and burrowing lifestyle.34 35 Selevin (Bashanov and Belosludov, 1941). Initially placed in Muridae based on its dental 39 formula, further analyses led to the first description of this species published in English 40 (Bashanov and Belosludov, 1941), in which it was placed in a new monospecific family, 41 Seleviniidae. These authors mentioned the close resemblance of the skull morphology of this 42 species with that of members of Gliridae (Myoxidae), but highlighted the atypical dental 43 structures within this species in comparison to dormice. Ognev (1947) identified the animal as 44 a highly derived dormouse and emphasised the resemblance of this species to Myomimus. He 45 therefore created the subfamily Seleviniinae within the family Gliridae. More recent analyses of the enamel structure in this animal and other dormice also incorporated Selevinia within 47 Gliridae, and no longer acknowledged Seleviniidae as a sister group of Gliridae (von Koenigswald, 1992). Storch (1994) assigned Myomimus and Chaetocauda to Seleviniinae 49 alongside Selevinia, regarding it as the most primitive of all extant dormice subfamilies. In 50 contrast, Yachontov and Potapova (1991) considered Selevinia to be more closely related to 51 Muscardinus and Glis, belonging to the subfamily Glirinae. Later, Potapova reasserted the close 52 relationship between Myomimus and Selevinia based on middle ear morphology (Potapova, 53 2001). Wahlert et al. (1993) placed Selevinia and Myomimus in the tribe Seleviniini, which, 54 joined with the tribe Leithiini, formed the subfamily Leithiinae. Due to the scarcity of accessible 55 specimens, Selevinia was not included in the phylogenetic analyses of the Gliridae based on 56 molecular data by Montgelard et al. (2003) or Nunome et al. (2007). The exact placement of ...

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.

The endemic dormouse Leithia melitensis from the Pleistocene of Sicily is considered an insular giant, whose body size is exceptionally large in comparison to that of any extant dormouse species. However, knowledge of the skull morphology of this giant glirid species is limited as cranial material is rare and mostly fragmentary. A fossil conglomerate representing a cave floor segment from Poggio Schinaldo, Sicily, presented an exceptional opportunity to reconstruct the cranium of Leithia melitensis. Following microCT scanning, five partial crania were digitally extracted from the conglomerate. A composite skull of the partial crania was then reconstructed with the use of merging and warping techniques, resulting in the best approximation to the complete skull morphology of this species thus far. All major structures except for the nasal bone are present in the composite model, indicating very robust morphology, especially in the zygomatic area and the pterygoid flange. This model could potentially be very important for our understanding of the morphology and ecology of this gigantic dormouse, as well as for providing valuable data for understanding the phenomenon of insular gigantism more generally.