Ortiz et al., 2012 - Microvertebrados Uquía

Despite a century of paleontological work in Neogene sequences of northwestern Argentina there is still much to learn about the biotic diversity in this area during Pliocene times. We report a rich microvertebrate assemblage recovered from Late Pliocene deposits of Uquía Formation, Jujuy Province, northernmost Argentina. Taxa represented in the studied sample include members of Bufonidae (Amphibia: Anura), Iguanoidea (Reptilia: Squamata), Passeriformes (Aves), Argyrolagidae, Didelphidae, Caviidae, Ctenomyidae, Octodontidae, and Cricetidae (Mammalia). Taphonomic attributes indicate that the bone concentration was produced by owls. The remains were disposed highly concentrated suggesting that the assemblage would have been generated in a short lapse, indicating a low time-averaging, retaining the main ecological signals of the past living community. The studied assemblage is noteworthy because it encompasses at least five new genera of cricetid rodents, illustrating the oldest record in northwestern Argentina for this diverse family of mammals. In spite of clear taxonomic differences at specific and generic levels, the structure of the assemblage is ecologically comparable to modern small mammal communities in terms of body mass distribution, trophic structure and abundance, with a dominance of cricetids over marsupials and caviomorph rodents. Striking differences in taxonomic composition between the Uquian assemblage and the coeval record from central Argentina indicate biogeographical distinctions since the Late Pliocene. The new Uquian cricetids show that the early divergence times for phyllotine genera proposed by several authors cannot be supported. The dominance of phyllotines in the assemblage as well as the record of Microcavia and an octodontid allow inferring arid or semiarid paleoenvironment conditions, in a more or less open habitat. The studied assemblage reflects a noteworthy faunal turnover, which implies the establishment of cricetid rodents as the dominant group in the small mammal communities. This faunal change can be associated to increasing aridity during Late Pliocene worldwide.

Palaeogeography, Palaeoclimatology, Palaeoecology, 2012

Despite a century of paleontological work in Neogene sequences of northwestern Argentina there is still much to learn about the biotic diversity in this area during Pliocene times. We report a rich microvertebrate assemblage recovered from Late Pliocene deposits of Uquía Formation, Jujuy Province, northernmost Argentina. Taxa represented in the studied sample include members of Bufonidae (Amphibia: Anura), Iguanoidea (Reptilia: Squamata), Passeriformes (Aves), Argyrolagidae, Didelphidae, Caviidae, Ctenomyidae, Octodontidae, and Cricetidae (Mammalia). Taphonomic attributes indicate that the bone concentration was produced by owls. The remains were disposed highly concentrated suggesting that the assemblage would have been generated in a short lapse, indicating a low time-averaging, retaining the main ecological signals of the past living community. The studied assemblage is noteworthy because it encompasses at least five new genera of cricetid rodents, illustrating the oldest record in northwestern Argentina for this diverse family of mammals. In spite of clear taxonomic differences at specific and generic levels, the structure of the assemblage is ecologically comparable to modern small mammal communities in terms of body mass distribution, trophic structure and abundance, with a dominance of cricetids over marsupials and caviomorph rodents. Striking differences in taxonomic composition between the Uquian assemblage and the coeval record from central Argentina indicate biogeographical distinctions since the Late Pliocene. The new Uquian cricetids show that the early divergence times for phyllotine genera proposed by several authors cannot be supported. The dominance of phyllotines in the assemblage as well as the record of Microcavia and an octodontid allow inferring arid or semiarid paleoenvironment conditions, in a more or less open habitat. The studied assemblage reflects a noteworthy faunal turnover, which implies the establishment of cricetid rodents as the dominant group in the small mammal communities. This faunal change can be associated to increasing aridity during Late Pliocene worldwide.

Journal of South American Earth Sciences, 2005

This article describes the first fossils recorded in the Hernandarias Formation (Pleistocene) in Entre Ríos province (eastern Argentina). They are represented by three teeth assigned to the caviomorph rodents (Rodentia, Mammalia) Aenigmys diamantensis gen. et sp. nov. and Eumysops. To establish the phylogenetic affinities of the two most enigmatic teeth, their enamel microstructure was studied. Aenigmys diamantensis is considered the most primitive taxon of a clade formed by Dinomyidae Neoepiblemidae Heptaxodontidae. Evidence of the close relationships among these families also is presented herein. The new fossils reinforce previous hypotheses about the survival of primitive Brazilian taxa after their extinction in the Pampas and Patagonia of southern South America. They also show that the diversity of caviomorph rodents during the Quaternary was greater than supposed and that an important Quaternary extinction, not previously detected, affected several lineages. With the available evidence, it is not possible to determine if these rodents indicate a warm pulse or a particular biogeographic situation in Entre Ríos.

Cricetid rodents of the Subfamily Sigmodontinae constitute one of the most diverse groups of extant New World mammals. Their fossil record in South America is restricted to the early Pliocene-Holocene interval. Recent findings in northwestern Argentina have expanded the paleontological knowledge of this group through several new localities from middle-late Pleistocene to late Holocene. These findings have allowed reconstruction of Quaternary paleoenvironmetal conditions in this region, mainly for the late Pleistocene-late Holocene interval. In three fossiliferous localities (La Angostura, Las Juntas, and Tafí del Valle) the presence of species below their present altitudinal range indicates the descent of vegetational belts in these mountainous areas during middle-late Pleistocene. In these Pleistocene small mammal communities species would have gone up and down following shifts and contraction of the vegetation belts. The oldest fossiliferous association -La Angostura-constitutes a non-analogue assemblage due to the altitudinal mixture of species living today at different vegetational belts. Evidence indicates that the modern sigmodontine assemblages were settling down at the end of Pleistocene and that all the genera and species were already present in the area with minor modifications. Holocene sigmodontine assemblages do not show substantial distributional changes but rather indicate variations in relative abundance. Changes in relative abundance appear to be related more to the impact of human activities than climatic oscillations of the last centuries. Shifts from natural environments to agroecosystems restructured the small mammal communities causing loss of specific diversity.

Interchange. Palaeogeography, Palaeoclimatology, Palaeoecology 267, 284-291) the potentially oldest South American Cricetidae (Rodentia) and Mustelidae (Carnivora) have been reported from a Late Miocene (Huayquerian) assemblage located in central Argentina (Caleufú site, La Pampa province). These findings expand the biochron of these important families in South America 3-4 Ma earlier than previous records. However, several observations prevent us from accepting the validity of these assumptions. In this paper we discuss the age of the Caleufú assemblage, and the assignment of the GHUNLPam 21722 to Mustelidae. The Caleufú assemblage contains a mixture of Pliocene and Late Miocene faunal elements, and has been assigned to the Huayquerian only due to the "stage of evolution" of some rodents. The lack of isotopic or paleomagnetic data coupled with the isolation of this locality and the absence of a local stratigraphic succession inhibit its correlation with other palaeontological comparable sites and a robust inference about its chronology. The "stage of evolution" of a taxon is not a biostratigraphic tool, thus we cannot rule out the possibility that the Caleufú assemblage has an Early Pliocene (Montehermosan) age. The GHUNLPam 21722, a poorly preserved specimen, shows several characters (e.g., 4 lower incisors, mental foramina below the incisors absent, third lower incisor smaller than the first and second ones) that do not match with Mustelidae (or Carnivora) but instead strongly resemble those observed in didelphimorphian marsupials. The discussed caveats regarding Caleufu assemblage chronology and taxonomy indicate that new and detailed studies are needed before the hypotheses advanced by Verzi and Montalvo can be accepted.

Reithrodon auritus is a living sigmodontine with one of the broader temporal records, from the lower Pliocene of Argentina. Its populations in northwestern Argentina are today found patchily and restricted to five high-elevation and isolated localities in open areas of highland grasslands vegetation (at > 3000 m). During the Pleistocene and early Holocene, R. auritus would have had a broader range, reaching lower altitudes everywhere and being one of the dominant small mammal species in some fossil localities. In this note, we summarize the known Pleistocene and early Holocene fossil record of R. auritus in northwestern Argentina, provide new paleontological sites for the species, and make comments concerning the paleoenvironmental implications of its presence at such lower altitudes. The paleontological evidence indicates that during the Pleistocene and early Holocene, R. auritus inhabited around 1000 m below their current altitudinal distribution in the eastern Andean ranges, with populations clearly more abundant than today. The fossils of R. auritus are indicative of colder and perhaps more xeric paleoenvironmental conditions, characterized by open areas with sparse grassy vegetation as those developed today around 3000 m elevation.

2010

We report a new vertebrate assemblage from the Pliocene Vergel Member of the San Gregorio Formation in northwestern Venezuela, which includes Crocodylia and Testudines indet., toxodonts, at least four species of xenarthrans of the Dasypodidae, Pampatheriidae, Glyptodontidae and Megatheriidae, and rodents. The last are Cardiatherium, cf. Caviodon (Hydrochoeridae), Neoepiblema (Neoepiblemidae), and what is here described as a new genus of a low-crowned octodontoid. cf. Caviodon is the first cardiomyine for northern South America. The rodent assemblage resembles in its ecological composition those of the late Miocene (Huayquerian) from the "Mesopotamian" of Argentina and the Acre region in Brazil, with partially overlapping systematic composition. The stratigraphic position of the San Gregorio Formation and mammals other than caviomorphs suggest a late Pliocene age for these sediments, implying the endurance of rodent taxa beyond their biochron in southern South America.

Two species of chinchillid rodents, Lagostomus (Lagostomopsis) incisus (Ameghino) and “Lagostomus (Lagostomopsis) spicatus” (Ameghino), have been recorded from the Monte Hermoso Formation (Montehermosan-Lower Chapadmalalan, early Pliocene) in southern Buenos Aires Province, eastern Argentina. L. (L.) incisus was based on skull remains, while “L. (L.) spicatus” was based on mandible remains and fragmentary skulls. Detailed study of specimens recovered from the upper section of the Monte Hermoso Formation, from the Irene “Formation” and the Chapadmalal Formation (late early-early late Pliocene, Buenos Aires Province), some of them represented by associated skull and mandible remains, indicates that L. (L.) incisus and “L. (L.) spicatus” are synonymous, with the valid name being L. (L.) incisus. The differences between both nominal species are here attributed to different ontogenetic states and sexual dimorphism. The stratigraphic provenance of the fossil material of L. (L.) incisus indicates a temporal distribution of this species restricted to the Montehermosan?-Chapadmalalan (early-early late Pliocene), instead of the Montehermosan (early Pliocene).