No 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.

Cavioidea sensu stricto groups three traditionally recognized families that are characterized by hypsodont, double-heart-shaped cheek teeth and moderate hystricognathy: Eocardiidae, Caviidae, and Hydrochoeridae. Eocardiidae was erected to include a diverse assemblage of extinct and plesiomorphic taxa, whereas Caviidae and Hydrochoeridae (the crown group of Cavioidea) include the lineages with extant representatives (cuyes, maras, and capybaras). A new genus and species of Cavioidea sensu stricto, Guiomys unica, is described here from the middle Miocene of west central Patagonia (Argentina). The new taxon is known from mandibular and maxillary fragments with molars, and isolated cheek teeth. A phylogenetic analysis of Cavioidea sensu stricto shows G. unica as the sister taxon of the clade formed by the crown group of Cavioidea sensu stricto ('medialis series'). The new species displays characters states intermediate between eocardiids and the 'medialis series.' The most outstanding character of Guiomys unica is the autapomorphic position of the notch for the insertion of the masseter medialis pars infraorbitalis muscle, isolated from both the masseteric and horizontal crests. This notch is located at the anterior end of the masseteric crest in eocardiids and represents the plesiomorphic state for Cavioidea sensu stricto. In caviids and hydrochoerids, the notch is located at the anterior end of the horizontal crest, the derived state for this character. G. unica allows reinterpretation of the homologies of the mandibular crests in basal cavioids and clarifies the evolutionary origins of crown-group cavioids (Caviidae + Hydrochoeridae).

No abstract

Fossil rodents from the Río Santa Cruz (RSC) classic localities (Santa Cruz Formation, Early-Middle Miocene) are known by the works of F. Ameghino and W.B. Scott since the end of the 19 th and beginning of the 20 th centuries. These caviomorph rodents have not been comprehensively reviewed since then. In this contribution, we studied new fossil specimens from the cliffs of the RSC (Province of Santa Cruz, Argentina) collected with accurate stratigraphic and geographic data during fieldtrips in 2013 and 2014. An increase in the caviomorph taxonomic richness is observed, based upon our taxonomic study of caviomorphs previously recorded in the RSC. Also, these fieldworks recovered for the first time several taxa previously found in other Santacrucian and even older Patagonian localities (Colhuehuapian, Early Miocene). As a general evolutionary pattern, we note an increase of derived euhypsodont taxa (Prolagostomus, Pliolagostomus, Schistomys, and Eocardia) in Segundas Barrancas Blancas (16.47-15.3 Ma). In addition, a taxonomic replacement of Phanomys by Schistomys is noted between Barrancas Blancas (17.21-16.3 Ma) and Segundas Barrancas Blancas, as well as a notably increase in the abundance of the large Perimys onustus in the latter locality. The present study provides a revision of the caviomorph systematics, and intends to be the starting point to understand the diversity (in all its aspects) and the evolution of this group during the Santacrucian, a major event in the South American mammalian history.

No abstract

BackgroundCaviidae is a diverse group of caviomorph rodents that is broadly distributed in South America and is divided into three highly divergent extant lineages: Caviinae (cavies), Dolichotinae (maras), and Hydrochoerinae (capybaras). The fossil record of Caviidae is only abundant and diverse since the late Miocene. Caviids belongs to Cavioidea sensu stricto (Cavioidea s.s.) that also includes a diverse assemblage of extinct taxa recorded from the late Oligocene to the middle Miocene of South America (“eocardiids”).ResultsA phylogenetic analysis combining morphological and molecular data is presented here, evaluating the time of diversification of selected nodes based on the calibration of phylogenetic trees with fossil taxa and the use of relaxed molecular clocks. This analysis reveals three major phases of diversification in the evolutionary history of Cavioidea s.s. The first two phases involve two successive radiations of extinct lineages that occurred during the late Oligocene and the early Miocene. The third phase consists of the diversification of Caviidae. The initial split of caviids is dated as middle Miocene by the fossil record. This date falls within the 95% higher probability distribution estimated by the relaxed Bayesian molecular clock, although the mean age estimate ages are 3.5 to 7 Myr older. The initial split of caviids is followed by an obscure period of poor fossil record (refered here as the Mayoan gap) and then by the appearance of highly differentiated modern lineages of caviids, which evidentially occurred at the late Miocene as indicated by both the fossil record and molecular clock estimates.ConclusionsThe integrated approach used here allowed us identifying the agreements and discrepancies of the fossil record and molecular clock estimates on the timing of the major events in cavioid evolution, revealing evolutionary patterns that would not have been possible to gather using only molecular or paleontological data alone.

Octodontoidea is the most speciose and ecologically diverse superfamily of caviomorph rodents. The systematic relationships of modern octodontoids is moderately accepted, however, the relationships of fossils (from the Eocene?-middle Miocene) are not clear. In recent years the hypothesis of a complex early evolution of the superfamily has emerged, with "basal octodontoids" representing different evolutionary lineages. The extinct family Acaremyidae may represent one such lineage, consisting of the genera Acaremys, Sciamys, Galileomys, and variably Platypittamys. In this work we describe a new octodontoid rodent recorded in post-Colloncuran? levels exposed at the locality of El Petiso, Northwest of Chubut Province, Argentina. Based on a systematic analysis of dental characters, we conclude that the new specimens correspond to a new species of Sciamys. Additionally, if the post-Colloncuran age for El Petiso is verified, the new species will extend the temporal range of the family Acaremyidae until, at least, the late middle Miocene, as well as the temporal range for the genus Sciamys from the Santacrucian SALMA. Our phylogenetic analyses corroborate the position of the new species as a member of Sciamys, and confirm that Acaremyidae represents an extinct family from Patagonian South America that lived until the middle Miocene. Massoiamys obliquus qualifies as morphological ancestor that pre-announces the octodontiform tooth pattern of octodontids. Thus, the octodontiform tooth pattern appears at least twice within the superfamily Octodontoidea.