They first appeared in the fossil record on Mallorca during the Early Pliocene (around 5 million years ago), presumably as a result to the evaporation of the Mediterranean sea during the Messinian salinity crisis (5.96-5.33 million years ago) connecting the Balearic Islands with mainland Europe.

They were one of only three native land mammals to the islands at the time of human arrival, alongside the shrew Nesiotites and goat-antelope Myotragus.

The divergence estimated by molecular clock between modern species of Eliomys and Hypnomys in a 2019 study was 13.67 million years ago.

[6] Hypnomys likely arrived in Mallorca during the Messinian salinity crisis (5.96–5.3 million years ago), 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.

Hypnomys, Myotragus and Nesiotites dispersed from Mallorca to Menorca during the Pliocene-Pleistocene transition as part of a faunal turnover event replacing the fauna of Menorca, which had previously differed from Mallorca (containing species such as the giant rabbit Nuralagus rex), likely due to the islands being connected during episodes of low sea level as a result of Pleistocene glaciation.

[8] The species Hypnomys gollcheri de Bruijn, 1966 from the Pleistocene of Malta has been assigned to the separate genus Maltamys.

[13] 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,[14] An analysis of the morphology of the lower jaw suggests that was probably efficient at gnawing and chewing.

A 2010 study concluded that H. morpheus was more terrestrial than living dormice, based on morphological comparison of the bone proportions.

[1] However, a 2014 study disputed this, finding based on the proportions of the limb bones that H. morpheus was likely arboreal, and possibly also had fossorial (digging) capabilities.

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.