History, taxonomy and palaeobiology of giant fossil rodents (Hystricognathi, Dinomyidae)

Introduction Among the great diversity of the order Rodentia, the “New World Hystricognathi”, or caviomorphs are a very characteristic group from the Neotropical region. This group, whose fossil record begins in the late Eocene (Antoine et al ., 2011), and is included in the infraorder Hystricognathi (Huchon and Douzery, 2001; Woods and Kilpatrick, 2005), comprises more than 50 genera in 13 families. One of the peculiarities of the extant caviomorphs is their wide range of size, between ∼200 g and ∼60 kg (Sanchez-Villagra et al ., 2003). The latter is the maximum body mass among extant rodents (Mones and Ojasti, 1986) and occurs in Hydrochoerus hydrochaeris (known colloquially as capybaras), considered the giant of the group. South America is also home of the pacarana, Dinomys branickii , a large, enigmatic caviomorph rodent that can be found in the rainforests of Brazil, Bolivia, Colombia, Ecuador and Peru (Figure 6.1). This is the only living member of the family Dinomyidae, which is notorious for its great past diversity (Frailey, 1986; Mones, 1986; Rinderknecht et al ., 2011). With a body mass that varies from 10 kg to 15 kg (White and Alberico, 1992), the pacarana is one of the biggest living rodents. However, dinomyid rodents used to be much larger. Many taxa from this family achieved extraordinary body sizes, especially those that belong to the extinct subfamily Eumegamyinae (Rinderknecht and Blanco, 2008). This subfamily contains the biggest rodents that ever existed (see Figures 6.2–6.4). Recorded since the middle Miocene (but see Krapovickas and Nasif, 2011), the diversity of the Dinomyidae has been repeatedly corroborated with a great number of findings. Nowadays, approximately 60 extinct species are known, all of them distributed within South America (Mones, 1986; Rinderknecht and Blanco, 2008; Rinderknecht et al ., 2011). In this chapter we summarize the principal aspects of the history, anatomy, systematics and taxonomy of these enigmatic rodents. All texts shown in square brackets and italics are translations from Spanish.