Main radiation events in Pan-Octodontoidea (Rodentia, Caviomorpha)

Abstract

Caviomorphs (South American hystricognaths) are recorded in the continent since the middle Eocene. The middle Eocene-early Oligocene is considered a key moment for their evolutionary history because by the early Oligocene they were differentiated into four superfamilies: Octodontoidea, Cavioidea, Chinchilloidea and Erethizontoidea. Due to their generalized dental patterns and abundance in the fossil record, Octodontoidea are interesting for analysing the origin and early history of caviomorphs. The phylogenetic relationships of the earliest octodontoids are studied herein. Results confirmed a basal caviomorph diversification in the middle Eocene (c. 45 Mya), with one lineage leading to Pan-Octodontoidea, and another leading to Erethizontoidea, Cavioidea and Chinchilloidea, which is not in accordance with analyses based on molecular data. Three major radiations were identified: the first one (late Eocene?/early Oligocene?) occurred in low latitudes with the differentiation of Pan-Octodontoidea and the earliest crown-Octodontoidea. The second radiation (late Oligocene) was a large-scale South American event; in the southernmost part of the continent it is recognized as the first Patagonian octodontoid radiation, which provided the characteristic high morphological disparity of the superfamily. The third radiation (late Miocene) is characterized by the replacement of 'old' by 'modern' octodontoids; the nature of this third event needs to be study in a broader taxonomic context.

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).…”

Systematic Revision and Evolutionary History of Acarechimys Patterson in Kraglievich, 1965 (Rodentia, Caviomorpha, Octodontoidea)

“…The ventral root of the zygoma extends slightly in front of the DP4 (Fig. 3.2), and its antero-posterior diameter is similar to its dorso-ventral diameter, unlike Pseudoacaremys kramarzi, where the antero-posterior diameter is twice the dorso-ventral one (Arnal and Vucetich, 2015). In ventral view, the masseteric tuberosity (for the origin of the masseter superficialis muscle, pars anterior) is conspicuous and continuous laterally with a shallow fossa for the origin of the masseter lateralis muscle.…”

“…In order to test the monophyly of the genus, we used an expanded and modified version of the data matrix of Arnal and Vucetich (2015) (Supplementary appendices 2 and 3). In total, it consists of 186 morphological characters and 59 taxa.…”

“…The rostral masseteric fossa (sensu Patterson and Wood, 1982) is shallow, subtriangular, and limited ventrally by the incisor tuberosity ( Fig. 3.2), unlike in Acaremys murinus, Pseudoacaremys kramarzi, and Sciamys principalis, in which the incisor tuberosity is included in the rostral masseteric fossa (Arnal and Vucetich, 2015). The dorsal root of the zygoma continues ventrally with a robust vertical ramus of the zygoma, similar to Sciamys principalis ( Fig.…”

First record of Banderomys leanzai Kramarz, 2005 (Rodentia, Caviomorpha) in Chubut Province, Patagonia (Argentina)

“…Dental nomenclature used here follows Arnal & Vucetich (2015). Upper tooth abbreviations: Al, anteroloph; Hf, hypoflexus; Ms, mesolophule; Msf, mesoflexus/mesofossette; Mt, metaflexus/ metafossette; Mel, metaloph; Pf, paraflexus/ parafossette; Prl, protoloph; Psl, posteroloph.…”