Hypnomys

The first remains of Hypnomys were discovered in 1910 on the island of Mallorca in the Balearic Islands by British palaeontologist Dorothea Bate, with remains also found by Bate on Menorca a year later. Upon first examination, Bate considered the fossils to represent those of Eliomys or Leithia, but in 1918 described the remains into the new genus Hypnomys, describing two species, H. morpheus on Mallorca, and H. mahonensis on Menorca. == Taxonomy and evolutionary history ==

Mitochondrial DNA from H. morpheus indicates that Hypnomys is a member of the subfamily Leithiinae, and closely related to the genus Eliomys, which contains (among others) the European garden dormouse (Eliomys quercinus). The divergence estimated by molecular clock between modern species of Eliomys and Hypnomys in a 2019 study was 13.67 million years ago. Cladogram of dormice showing the placement of Hypnomys after Bover et al. 2020 }} }} }}}}}}}}}}}} The ancestor of Hypnomys is often assumed to be the prehistoric Eliomys species E. truci, known from the latest Miocene of the Iberian Peninsula. an event when the Strait of Gibraltar closed and the Mediterranean evaporated, with the resulting sea level drop causing the exposure of the continental shelf, allowing dispersal from the Iberian Peninsula to the Balearic Islands, before the islands again became isolated following the reopening of the Straits of Gibraltar and the resulting Zanclean flood which refilled the Mediterranean approximately 5.3 million years ago, at the beginning of the Pliocene. The species Hypnomys gollcheri de Bruijn, 1966 from the Pleistocene of Malta has been assigned to the separate genus ''Maltamys. it has generally been considered distinct by other authors. == Description ==

(Eliomys quercinus) including the giant population from Formentera (centre), and normal morphology (right) The overall body size of Hypnomys is considerably larger than mainland dormice species, with the overall body size of the lineage gradually increasing over time. An articulated specimen of Hypnomys cf. onicensis measured in a 2010 study had a head and body length of around and a tail length of around . A specimen of H. morpheus measured in the same study was found to have a head and body length of about and a tail length of about . The tail lengths are proportionally shorter than in species of Eliomys. The specimen of H. morpheus was estimated to weigh between . The limbs are also robust, with elongated zygopodiums (part of the limbs between the foot and elbow/knee) on both hind and forelimbs. == Paleobiology ==

A 2016 bone histology study found that H. onicensis could live over 10 years, an exceptionally long lifespan in comparison to living Eliomys, which can only live up to 5 years. Young juveniles were found to be already substantially larger than equivalently aged Eliomys individuals. Sexual maturity was also likely delayed in comparison to living Eliomys. In a dental microwear study of H. morpheus the high number of fine scratches on the teeth suggests that the species was more omnivorous than the garden dormouse (which is heavily carnivorous), with the presence of pits on the teeth indicating the intake of hard food such as nuts and seeds, or grit, An analysis of the morphology of the lower jaw suggests that was probably efficient at gnawing and chewing. The lifestyle of Hypnomys has been debated. A 2010 study concluded that H. morpheus was more terrestrial than living dormice, based on morphological comparison of the bone proportions. Analysis of the cribriform plate of a probable specimen of H. morpheus suggests that the species probably had a well developed senses of sight, hearing and smell, the last possibly better developed than the living garden dormice. The former two have been suggested to have been for detecting predators, while the last aided in finding food. While the Balearic Islands lacked large terrestrial predators, Hypnomys was hunted by birds of prey such as owls which are known to have inhabited the islands. == Extinction ==

Like the two other endemic mammal genera on the Balearic islands, the shrew Nesiotites and the goat-antelope Myotragus, Hypnomys likely rapidly became extinct after human arrival in the Balearic islands during the mid-late 3rd millennium BC. The youngest current radiocarbon dates for H. morpheus are a few thousand years prior to human arrival, but later dates much closer to human arrival for Nesiotites and Myotragus suggest that it was also present at the time of arrival. Direct predation by humans is an unlikely cause of extinction for Hypnomys. Predators currently present on the Balearic Islands such as cats, weasels, martins and genets were introduced to the islands long after the extinction of the endemic mammals, and there is no compelling evidence for the early presence of dogs. The garden dormouse (Eliomys quercinus) and wood mouse (Apodemus sylvaticus) were early introductions to the islands and may have competed with Hypnomys, though there is no concrete evidence that their existences overlapped. Diseases spread by introduced species may have contributed to the extinction. The two other native pre-human terrestrial vertebrates of Mallorca and Menorca, the still living Lilford's wall lizard (Podarcis lilfordi) and Majorcan midwife toad (Alytes muletensis) have been heavily impacted by human presence on the archipelago, and today are only confined to remote areas. == See also ==