Evolutionary pattern of Metacaremys gen. nov. (Rodentia, Octodontidae) and its biochronological implications for the late Miocene and early Pliocene of southern South America

Abstract

We analyse the taxonomic status and diversity of the late Miocene Octodontoidea (Hystricognathi) Cercomys primitiva and related samples, a taxon previously known only from the holotype specimen. New findings associated with an extensive review of late Miocene and early Pliocene rodents have allowed us to recognize the occurrence of this and other related species in several localities of central and western Argentina, and in south‐central Bolivia. We discuss the invalidity of Cercomys and propose the new genus Metacaremys, which includes the type species Metacaremys primitiva comb. nov. and two new species, Metacaremys calfucalel sp. nov. and Metacaremys dimi sp. nov. Osteological, brain and dental morphology show that the new genus is not related to Brazilian Echimyidae, as previously considered, but to the southern family Octodontidae. Although the molar morphology of this genus is quite conservative, comparison of the samples shows a variation in size. We discuss the plausible evolutionary pattern explaining this variation and the implied biochronological and biostratigraphical information. It is recognized as an anagenetic lineage in which an increase in size occurs from the oldest species, M. primitiva comb. nov. (early late Miocene, c. 9.23 Ma), to the youngest species, M. dimi sp. nov. (Miocene–Pliocene boundary, c. 5.28 Ma). Metacaremys calfucalel is intermediate in size and age between these two species. The polarity of this pattern of change is consistent with that shown by other partially synchronous independent lineages of octodontoids, thus providing new evidence for the biochronological and biostratigraphic scheme of the late Miocene and early Pliocene of southern South America.

On the validity of the Macrochorobates scalabrinii Biozone (early Huayquerian Stage/Age, Late Miocene). Multi-proxy analysis of the enigmatic Arenas Blancas site (Buenos Aires Province, Argentina)

“…We follow and discuss the biostratigraphic schemes proposed by Cione and Tonni (2005), Verzi et al ( , 2011, Sostillo et al (2014), Deschamps and Tomassini (2016), Tomassini et al (2017), Montalvo et al (2019), andPiñero et al (2021). We use the terms Chasicoan and Huayquerian to make reference to the assemblages (e.g., Chasicoan assemblage) represented in each stage/age of the different sites studied.…”

“…Folguera and Zárate (2009) proposed that different Late Miocene units cropping out in the southwestern Buenos Aires Province, including Arroyo Chasicó, Epecuén, and Saldungaray formations, should be referred to the CAF, which is widely extended in La Pampa Province and was defined on lithostratigraphic criteria (Folguera et al, 2017). This proposal was considered in several recent paleontological works (e.g., Deschamps and Tomassini, 2016;Montalvo et al, 2019;Piñero et al, 2021;Schmidt et al, 2022) and it is also accepted for this study.…”

“…Mammal assemblages recovered from this area are of great importance because they have been used as the basis of the biochronostratigraphic schemes applied in different regions of South America (Cione and Tonni, 2005;Montalvo et al, Cerro Azul Formation (CAF; sensu Linares et al, 1980). Vertebrate assemblage from these levels was assigned to the Chasicoan Stage/Age (e.g., Pascual, 1961;Fidalgo et al, 1978Fidalgo et al, , 1987Bondesio et al, 1980;Piñero et al, 2021).…”

New Miocene–Pliocene Specimens of Toxodontidae (Notoungulata) from the Huayquerías of Mendoza, West-Central Argentina

“…were the basis for the establishment of the Huayquerian Stage/Age (Simpson, 1940) and the Huayquerian South American Land Mammal Age (Pascual et al, 1965), representing the latest Miocene, with few characteristic taxa. Nevertheless, through the years, the Huayquerian fauna was redefined based on faunal assemblages from other coetaneous Argentinean areas, such as Catamarca Province (e.g., Marshall & Patterson, 1981) or even with undated assemblages from La Pampa and Buenos Aires provinces (e.g., Pascual et al, 1965;Verzi et al, 2008;Piñero et al, 2021;Tomassini et al, 2023). The time span of the Huayquerian Stage/Age is still unclear.…”

“…By contrast, its end is debatable, as it lacks reliable dating; some authors have proposed that it does not cross the Miocene/Pliocene boundary (e.g., Reguero & Candela, 2011), while others have argued that it reaches the Early Pliocene (e.g., Marshall et al, 1979;Verzi et al, 2008;Prevosti et al, 2021;Piñero et al, 2021). Fortunately, this panorama is changing thanks to new research in the Huayquerías del Este, initiated in 2013.…”