New rodents (Mammalia) from the late Oligocene of Cabeza Blanca (Chubut) and the first rodent radiation in Patagonia

Abstract

Caviomorph rodents, the New World Hystricognathi, are one of the most characteristic groups of South American mammals. Although they have been in the continent at least since the middle Eocene, those of the Deseadan Land mammal Age (early-late Oligocene) are the best source to understanding their early history due of their good record, large geographic distribution and good temporal calibration of many of the local faunas. Here, we describe the following new taxa from the classical locality of Cabeza Blanca: Octodontoidea Acaremyidae Galileomys baios n. sp., Octodontoidea incertae sedis Ethelomys loomisi n. gen., n. comb., Acarechimys leucotheae n. sp., Protacaremys? adilos n. sp., Chinchilloidea incertae sedis Loncolicu tretos n. gen., n. sp., Incamys menniorum n. sp., Caviomorpha incertae sedis Llitun notuca n. gen., n. sp., Leucokephalos zeffiae n. gen., n. sp. and Cephalomyidae Cephalomys ceciae n. sp. The DP4 of an 'eocardiid', Asteromys punctus? is described for the first time. These new taxa allow us to reinterpret the relationships of some of the previously known Deseadan species and genera. They show a great early diversification at least for extra Andean Patagonia, involving at least three of the main caviomorph lineages: octodontoids, chinchilloids and cavioids.

Late middle Eocene caviomorph rodents from Contamana, Peruvian Amazonia

“…Put together, with the presence of caviomorphs showing very primitive features (i.e., Cachiyacuy and Canaanimys), these low diversity and disparity suggest that a short time range of caviomorph evolutionary history had undergone in South America prior this early Contamanan rodent record, as already proposed by Antoine et al (2012). Although these localities potentially document the first representatives of octodontoids (Eoespina) and cavioids (Eobranisamys), they probably predate the early adaptive radiation(s) of Oligocene-Neogene caviomorph communities (including obligate representatives of extant superfamilies), which is consistent with the results of Arnal and Vucetich (2015) and Vucetich et al (2015).…”

“…A reduced second cristid is also found in Draconomys Vucetich et al, 2015, Leucokephalos, Platypittamys, Deseadomys Wood andPatterson, 1959, and Incamys. As for Eoincamys, the p4 of P. ucayaliensis is relatively shorter with respect to the p4 of Draconomys, Leucokephalos, Platypittamys, Deseadomys, and Incamys (Wood, 1949;Wood and Patterson, 1959;Hoffstetter and Lavocat, 1970;Lavocat, 1976;Vucetich et al, 2010Vucetich et al, , 2015. Besides, the MUSM 2821 p4 (Figure 6.2) differs from Platypittamys and Deseadomys in the presence of a hypolophid.…”

“…However, the particular characteristics of the dp4 and the tetralophodont pattern of upper molars do not allow for a formal generic assignment. Branisamys was initially attributed to the Dasyproctidae (i.e., Cavioidae) by Lavocat (1976), but this genus may be more closely related to the Chinchilloidea following Kramarz et al (2013) and Vucetich et al (2015). Eobranisamys was originally assigned to the Cavioidea (Frailey and Campbell, 2004), but its alleged close relationship with Branisamys would question, in turn, the suprafamilial attribution of Eobranisamys.…”

“…Kramarz et al, 2013). Indeed, the leading edges are thicker than the trailing edges in Incamys and most chinchilloids (Kramarz et al, 2013;Vucetich et al, 2015). MUSM 2833 differs from all aforementioned taxa in having a shorter protoloph and third transverse crest.…”

“…The size of these specimens is comparable to that of Cachiyacuy kummeli, Canaanimys maquiensis, Eoespina woodi/Eosachacui lavocati, and Eoincamys ameghinoi Frailey and Campbell, 2004. On the lateral view of the MUSM 2822 mandible ( Figure 6.5), the general disposition and strong development of the masseteric crest on the dentary is found in all Paleogene caviomorphs for which the mandible is known (e.g., Eobranisamys, Andemys Bertrand et al, 2012, Platypittamys Wood, 1949, Scotamys Loomis, 1914, Cephalomys Ameghino, 1897, Branisamys, Incamys Hoffstetter and Lavocat, 1970, Sallamys, Migraveramus Patterson and Wood, 1982, Paulacoutomys Vucetich et al, 1993, Galileomys Vucetich and Kramarz, 2003, Acarechimys Patterson, 1965(in Patterson and Wood, 1982, Leucokephalos Vucetich et al, 2015, Loncolicu Vucetich et al, 2015, and Llitun Vucetich et al, 2015. Contrary to MUSM 2822, Galileomys and Paulacoutomys develop a very thin lateral crest, stemming from the ascending ramus, and almost reaching the masseteric crest below the m1.…”