The oldest sigmodontine rodent revisited and the age of the first South American cricetids

Abstract

New fossil material ofAuliscomys formosusReig 1978 allows restudy of the oldest known South American representative of the subfamily Sigmodontinae. Description ofAuliscomys formosuswas based on a fragmentary dentary exhumed from the Monte Hermoso Formation of central Argentina. Previous studies allocatedA. formosusto the early Pliocene. A reevaluation of dental and cranial morphology, including for the first time the upper dentition, and the inclusion ofA. formosusin a phylogenetic analysis of the tribe Phyllotini indicate thatA. formosusrepresents a new genus,Kraglievichimys.Kraglievichimysshares a mosaic of characters with the livingAuliscomysOsgood, 1915 andLoxodontomysOsgood, 1947. The taxonomic reassignment ofA. formosusand the possibility that the Monte Hermoso Formation may be younger than early Pliocene in age provide a new understanding of cricetid diversification in South America. Estimates of sigmodontine ancestry by molecular approaches are biased toward older ages, whereas this new interpretation of the history ofK. formosussuggests that the South American history of sigmodontines spans less than 4 million years.UUID:http://zoobank.org/49dd8f60-56b1-4e8a-a044-6cea3a1bd52b

New radiometric 40Ar–39Ar dates and faunistic analyses refine evolutionary dynamics of Neogene vertebrate assemblages in southern South America

“…The only other pertinent discovery concerns a tiny molar fragment from the Late Miocene Andalhuala Fm (ca. 7 Ma) that was originally assigned to Sigmodontinae 51 , but later questioned due to its fragmentary condition 52 . The Cerro Azul assemblages from Caleufú and El Guanaco localities include cricetid remains 36 – 47 .…”

Morphological similarity and dental homologies in two sigmodontine rodents (Mammalia, Cricetidae) from different tribes: A topological analysis to explore convergence

“…With the advance of wear, some elements of the cuspal level may be fused into a same dentine “channel,” forming then a so‐called hybrid structure (Barbière, Ortiz, & Pardiñas, 2019). The hybrid structures which develop in the distinct flexi/ids are referred to in the ICAMER system as complexes.…”

“…Paradigmatic examples are the genera previously allocated to the so‐called Reithrodon group of the tribe Phyllotini (sensu Olds & Anderson, 1989; see also Hershkovitz, 1955; Ortiz et al, 2000; Steppan & Pardiñas, 1998), now included in two tribes (i.e., Euneomyini and Reithrodontini; Pardiñas et al, 2015; Pardiñas et al, 2017). Similar issues are even more acute when dealing with the study of fossil forms, as the description of most of the extinct sigmodontines is based on dental material (e.g., Barbière, Ortiz, & Pardiñas, 2019; Pardiñas, 2008; Reig, 1987; Steppan & Pardiñas, 1998). Indeed, several fossil genera are seriously compromised in their tribal allocations given the current stage of systematics dominated by molecular‐based phylogenies (Ronez et al, 2020).…”

On the Supposed Presence of Miocene Tayassuidae and Dromomerycinae (Mammalia, Cetartiodactyla) in South America

“…The last of the three phases described above is known as the Great American Biotic Interchange (GABI), and is considered one of the most significant biogeographic events of the Cenozoic (Webb, 1976(Webb, , 1991Cione et al, 2015). During the GABI, it is generally agreed that initial and limited exchange occurred during the late Miocene and early Pliocene; procyonid carnivorans and sigmodontine rodents were the first northern immigrants in South America, and two types of ground sloths were the first southern immigrants to Mexico and the southern United States (Woodburne, 2010;Cione et al, 2015;Barbiére et al, 2019;Engelman and Croft, 2019). Procyonid carnivorans, such as Cyonasua and Chapalmalania, are known from the Huayquerian South American Land-Mammal "Age" (SALMA) of Argentina and Uruguay (late Miocene, 9.0-6.8 Ma) (Reguero and Candela, 2011;Prevosti and Soibelzon, 2012;Prevosti et al, 2013;Engelman and Croft, 2019;Soibelzon et al, 2019).…”

“…Mustelids have also been reported from the Huayquerian SALMA (Verzi and Montalvo, 2008), but this has been refuted by Prevosti and Pardiñas (2009). The oldest cricetid (sigmodontine) rodent in South America is from the Montehermosan SALMA, but whether it is late Miocene or early Pliocene in age is uncertain (Barbiére et al, 2019). Molecular analyses have suggested an earlier arrival of sigmodontines (Parada et al, 2013;Leite et al, 2014;Maestri et al, 2019), but fossil evidence supporting this is lacking.…”