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. Radiocarbon dates indicate that it became extinct after the European arrival in the archipelago sometime after 1270 AD, probably due to the introduction of rats.[1]
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 were 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). A 2012 genomic study recovered it as a highly divergent lineage within the genus Mus sensu lato most closely related to Coelomys.[2]
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.