Diversity and evolution of femoral variation in ctenohystrica

Despite possessing a rather generalised postcranial skeleton, rodents are on average capable of a wide variety of locomotory behaviours, such as swimming, digging and climbing (Nowak, 1999). Particularly, rodents belonging to Ctenohystrica (sensu Huchon et al., 2002, and Fabre et al., 2012: Ctenodactylidae, Diatomyidae and Hystricognathi) display a diversity of locomotory styles and encompass a large range in body mass from approximately 50 g for the naked mole-rat Heterocephalus glaber to aroand 60 kg for the largest living rodent, the capybara Hydrochoerus hydrochaeris, consequently filling many different ecological niches (e.g. MacDonald, 2009; Wilson and Sánchez-Villagra, 2009, 2010). Moreover, this diversity is greatly expanded by the inclusion of giant extinct members such as Phoberomys, Arazamys and Josephoartigasia that reached body masses at least seven or eight times that of the capybara (Sánchez-Villagra et al., 2003; Rinderknecht and Blanco, 2008; Rinderknecht and Bostelmann, 2011). The adaptive diversity that characterises the evolution of Ctenohystrica, and particularly the Caviomorpha, a group that dispersed from Africa to colonise South America (Poux et al., 2006; Rowe et al., 2010) and evolved on that continent during a period of splendid isolation in the Cenozoic, has been the subject of numerous morpho-functional and evolutionary studies (e.g. Verzi et al., 2010; Wilson et al., 2010; Álvarez et al., 2011a, b; Hautier et al., 2011, 2012; Cox et al., 2012; Geiger et al., 2013; Wilson, 2013). The interplay between form and function has been studied in the postcranial skeleton of a number of mammals (e.g. Kappelman, 19; Anemone, 1990;White, 1993; Vizcaíno and Milne, 2002; Kley and Kearney, 2007; Meachen-Samuels, 2010), and studies of Ctenohystrica have, for example, examined individual bones (e.g. Seckel and Janis, 2008; Morgan, 2009; Steiner-Souza et al., 2010; Elissamburu and De Santis, 2011), long bones (Biknevicius, 1993; Elissamburu and Vizcaino, 2004; Samuels and Van Valkenburgh, 2008; Morgan and Álvarez, 2013) and the autopodial skeleton (e.g. Weisbecker and Schmid, 2007; Morgan and Verzi, 2011). These studies have used morphological traits, described as ratios or quantified using biomechanical indices or geometric morphometric descriptors of shape, to identify functional specialisations and instances of adaptive convergence underpinned by shared function and/or ecology.