The Lava Mouse, Malpaisomys insularis, is an extinct endemic rodent from the Canary Islands, Spain. It is the only species in the genus Malpaisomys.
The Lava Mouse is known from Holocene and Pleistocene deposits in the eastern Canary Islands, including Fuerteventura, Lanzarote and nearby islets. It became extinct during prehistoric times, probably because of the arrival of humans and the livestock (such as dogs) they brought with them.
A study of its skeletal characteristics suggested that the Lava Mouse lived in fissures opened in the lava fields (Boye et al. 1992). The morphology of its teeth indicates that it was an herbivore (Renaud & Michaux 2004).
Its evolutionary relationships are unresolved due to its fairly generic morphology. Rodents on islands generally increase in size during the course of their evolution (see also insular gigantism); the lava mouse was fairly small for an insular rodent (some 20 cm in overall length: Boye et al. 1992). Thus, it is more likely than not that it evolved from small Pliocene mainland genera Paraethomys, Occitanomys, or relatives thereof, than being a later derivative of the Deomyinae (Renaud & Michaux 2004).
This rodent owes its name Malpaisomys to the Spanish word malpaís ("badlands"), denoting the lava fields where its fossil remains are sometimes found in cavities.