M us in M orocco: a Quaternary sequence of intraspecific evolution

North A frica is an intricate biogeographical region at the crossroads of immigration waves from tropical A frica and A sia. Species confined between various barriers ( A tlas M ountains, arid environments such as the S ahara in the s outh, water masses such as the M editerranean S ea in the n orth, and the A tlantic O cean in the w est) were generally forced to adapt locally to environmental changes instead of tracking their habitat by shifting their distribution area. The present study aims at providing first insight into the evolution of the genus M us , and more specifically of the western Mediterranean species M us spretus in this area. The study relies on the abundant L ate P leistocene and M iddle H olocene fossil assemblage from the E l H arhoura 2 cave ( R abat‐ T émara, M orocco). This exceptional record was studied using geometric morphometrics applied to first upper and lower molars, constituting the most informative and best preserved fossil remains for such small rodents. Two main issues were addressed. (1) Geometric morphometrics was used to clarify taxonomic status and phylogenetic relationships among fossil and modern species in this area. Morphometric analysis revealed good discrimination of most modern and fossil species but failed to document intermediate forms tracing anagenetic evolution. Not mutually exclusive, the occurrence of complex processes of morphological evolution in this genus such as parallel evolution and the action of stabilizing selection may make it difficult to translate patterns of morphological evolution into phylogenetic conclusions. (2) The record was shown to document a sequence of intraspecific evolution of M . spretus . The morphology of the molars through the fossil record of E l H arhoura 2 was surprisingly stable despite extensive modern variation. The limited temporal variation largely failed to correlate to palaeoenvironmental proxies. The mouse fossil record at E l H arhoura 2 thus presents an intriguing case of morphological stasis despite extensive environmental changes. This long‐term stability may have been recently perturbed by anthropogenic factors including landscape changes and introduction of various competitors and predators, leading to a size reduction. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society , 2013, 109 , 599–621.