Understanding mammalian tooth crown morphological changes during evolution constitutes a crucial area of investigation common to both palaeontology and developmental biology (Osborn, 1907; Hershkovitz, 1962; Hunter and Jernvall, 1994; Jernvall, 2000; Kangas et al., 2004; Kavanagh et al., 2007; Charles et al., 2009a,b; Harjunmaa et al., 2012). During the past two decades, relationships between tooth morphology, diet and mastication have been deciphered through topographic analyses of the crown surface (e.g. Reed, 1997; Jernvall and Selänne, 1999; Evans et al., 2007; Lazzari et al., 2008a,b; Boyer et al., 2010;Wilson et al., 2012). Such an approach allowed the investigation of several well-documented primate, rodent and multituberculate lineages showing drastic modifications of dental morphology.
Including about one third of modern mammalian biodiversity, present in all the main continental landmasses except Antarctica and New Zealand, the superfamily Muroidea (rats, mice, gerbils, hamsters, voles … sensu Musser and Carleton, 2005) displays a huge diversity of cheek teeth in terms of cusp arrangement and crown elevation, that can be associated with different masticatory modes and diets (Butler 1980, 1985; Lazzari et al., 2008b, 2011; Coillot et al., 2013). It has also a very rich fossil record, and a now well-established phylogeny concerning extant species (Jansa and Weksler, 2004; Steppan et al., 2004; Jansa et al., 2009; Fabre et al., 2012).
For these reasons, Muroidea are exceptional in providing many examples that can be used to study the modalities and mechanisms of molar crown diversification not only because the fossil record of many muroid subfamilies is well-documented but because there are many cases of parallel and convergent evolutions of dental morphologies. Such convergences involve the recurrent emergences of supplementary cusps, but also hypsodonty, lophodonty (formation of crests) or formation of prismatic crowns. These convergences alter the phylogenetic signal carried by the teeth and greatly complicate morphological cladistic studies (De Bruijn et al., 1996).