Reconstructing a giant fossil dormouse

Lay summary authored by Jesse Hennekam. Read the full paper here: https://doi.org/10.5334/oq.79

The ‘island effect’ is an evolutionary phenomenon that describes how animals often evolve substantial changes in body size when isolated on islands. More specifically, large mammals become smaller (e.g. dwarfed elephants and hippopotamuses), whilst small mammals (notably rodents, lagomorphs and insectivores) become larger relative to their mainland relatives. This latter process of insular gigantism is well known from Mediterranean islands over the last 12 million years. In particular, dormice have experienced this phenomenon on multiple occasions, with the exceptionally large species, Leithia melitensis from the Pleistocene of Sicily and Malta, reaching the size of a domestic cat. Although many fossils of the lower jaw are known of this species, the skull was previously only known from fragmentary material.

image 1- skull

Figure 1: A sketch of the lateral view of the composite skull of the gigantic dormouse Leithia melitensis. Credit: James W. F. Sadler.

In their study published in Open Quaternary, the lead author noticed a section of cave floor on display at the Palermo Museum. This floor segment had been excavated from Poggio Schinaldo Cave, Sicily, during the construction of a motorway in the 1970s. A number of rodent skulls could be seen on the surface of this rock segment. By investigating the dentition of one of the skulls, it was clear that these fossils were in fact the giant dormouse Leithia melitensis. Considering the rarity of cranial material belonging to this species, the segment was transported to Basel, Switzerland. The microCT scanning facility here was used to scan two sections of the cave floor, enabling the researchers to visualise the interior of the rock. The rock segment turned out to be a conglomerate of fossil material including at least five partial skulls of Leithia melitensis. Virtual reconstruction based on the differences in density between bone and matrix was used to extract 3D models of the partial skulls. The best preserved features of these skulls were then combined to create an almost complete composite skull. This composite represents the best approximation of the complete skull morphology of Leithia melitensis known so far, and will aid palaeontologists in making inferences about the lifestyle and behaviour of this fascinating extinct giant dormouse.

image 2- reconstruction

Picture 2: Reconstruction of the Pleistocene giant dormouse, Leithia melitensis (left), and its nearest living relative the garden dormouse, Eliomys quercinus (right). Credit: James W. F. Sadler.

Full paper: Hennekam, J.J., Herridge, V.L., Costeur, L., Di Patti, C. and Cox, P.G., 2020. Virtual Cranial Reconstruction of the Endemic Gigantic Dormouse Leithia melitensis (Rodentia, Gliridae) from Poggio Schinaldo, Sicily. Open Quaternary, 6(1), p.7. DOI: http://doi.org/10.5334/oq.79

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