A new echimyid genus (Rodentia, Caviomorpha) in Central Argentina: uncovered diversity of a Brazilian group of mammals in the Pleistocene

Abstract

We describe a new extinct spiny rat, Proclinodontomys dondasi n. gen. n. sp. (Rodentia, Caviomorpha, Echimyidae), represented by a noteworthy preserved skull and mandible from the early-middle Pleistocene outcrops at the coastal cliffs of SE Buenos Aires Province (Central Argentina). Phylogenetic analyses allow us to propose that the new species described here and the already known Eurzygomatomys mordax (Winge) represent a new genus closely related to the living Euryzygomatomys spinosus and Clyomys laticeps. The new genus differs from Euryzygomatomys and Clyomys by having much more procumbent upper incisors, a more developed fossa for the M. temporalis, more flared and laterally expanded zygomatic arches, frontal less markedly expanded posteriorly, jugals much deeper anteriorly than posteriorly, with the dorsal border descending more abruptly posteriorly, smaller orbital cavity, and external auditory meatus relatively smaller and slanted upward and backward. Several features of the new species reflect a higher degree of adaptation to semifossorial habits than those of E. spinosus. The origin of the semifossorial ecomorphotype within echimyids may have been triggered by the expansion of relatively open and arid environments that arose near the Miocene-Pliocene boundary. The record of this new echimyid in Central Argentina indicates that during the early-middle Pleistocene, the southern limit of the geographic range of extinct representatives of the Brazilian lineage of semifossorial echimyids extended farther south than that of their living members.UUID: http://zoobank.org/c30ec1fe-4352-4867-a02f-e0d45c884bfe

Paralonchothrix gen. nov., the first record of Echimyini (Rodentia, Octodontoidea) in the late Miocene of Southern South America

“…Late Oligocene to middle Miocene representatives are related to living arboreal Echimyini (sensu Fabre et al 2017) from Amazonian and Atlantic forests, which agrees with the persistence of forests with tropical elements as far as southern Argentina in this period (Palazzesi & Barreda 2007). From the late Miocene on, southern fossil echimyids belong to lineages of terrestrial and fossorial Euryzygomatomyinae and Myocastorini (sensu Fabre et al 2017) that currently inhabit open, shrubby to grassland environments, and dry forests (Reig 1986;Verzi et al 1994Verzi et al , 1995Verzi et al , 2014Verzi et al , 2016Verzi et al , 2019Vucetich 1995;Vucetich et al 1997;Cartelle 1999;Hadler et al 2008;Olivares et al 2012bOlivares et al , 2017Olivares et al , 2020Sostillo et al 2015;Candela et al 2020). This taxonomic composition of the fossil record of echimyids is concurrent with Cenozoic palaeoclimatic changes (Pascual & Ortiz Jaureguizar 1990;Janis 1993;Denton 1999;Zachos et al 2001Zachos et al , 2008Tripati et al 2009;Arakaki et al 2011;Le Roux 2012;Palazzesi & Barreda 2012;Dunn et al 2015).…”

“…The new genus Paralonchothrix increases the diversity of both the extinct echimyids in southern South America (Olivares et al 2017;Candela et al 2020) and the clade that includes the living Mesomys and Lonchothrix (Lara et al 1996;Leite & Patton 2002;Galewski et al 2005;Upham & Patterson 2012Emmons & Fabre 2018). Our systematic and phylogenetic analyses show that the closest relative of Paralonchothrix is the monotypic Lonchothrix, and both are sister to Mesomys.…”

“…These ecological transitions promoted changes in the taxonomic composition of the fossil echimyid fauna from the Patagonia Subregion. Thereby, southern echimyids recorded since the late Miocene are restricted to lineages of Euryzygomatomyinae (sensu Emmons 2005) and Myocastorini (sensu Fabre et al 2017) that currently occupy open, shrubby to grassland environments and dry forests in the Chacoan Dominion (sensu Morrone 2014) (e.g., Reig 1986;Verzi et al 1994Verzi et al , 1995Verzi et al , 2004Verzi et al , 2015Verzi et al , 2016Verzi et al , 2018Vucetich 1995;Cartelle 1999;Hadler et al 2008;Olivares et al 2012aOlivares et al , b, 2017Sostillo et al 2015;Candela et al 2020). That is the case of some material assigned to Eumysopinae indet.…”

“…Only the roots of the dp4 are preserved in both specimens. The lower molars are subquadrangular and tetralophodont, different from those in the most of extinct southern Echimyidae that are trilophodont (see Verzi et al 1994Verzi et al , 1995Verzi et al , 2015Verzi et al , 2018Vucetich 1995;Olivares et al 2012aOlivares et al , b, 2017Candela et al 2020). The extinct Paramyocastor (see Verzi et al 2002) and Tramyocastor (see Rusconi 1936), and the extant Myocastor coypus also have tetralophodont molars, with the mesolophid as a complete crest.…”

Geologically calibrated mammalian tree and its correlation with global events, including the emergence of humans

“…The expansion of C4 grasses was a global phenomenon that also included North America and South America, beginning in the late Miocene and persisting to the present day, including the present glacial–interglacial period (Cerling et al., 1997 ). Rodentia in Argentina may have been triggered by the expansion of relatively open and arid environments that arose near the Miocene‐Pliocene boundary (Candela et al., 2019 ). This event may have impacted Hominidae radiation as well as Laurasiatheria, such as Bovidae and Equidae in tropical savannah and temperate prairies and steppe (Taira, 2007 ).…”