Cecilia Marcela Deschamps

Ontogeny and diversity of the oldest capybaras (Rodentia: Hydrochoeridae; late Miocene of Argentina)

Abstract According to our previous model for interpreting the fossil record of capybaras the cheek teeth grow in width and length throughout life; flexids (especially h.s.i. and h.t.i.) deepen allometrically resulting in diverse occlusal morphologies during ontogeny; in the more derived species the ‘onset’ of flexid development is pre-displaced, and the relative depth and development rate of the flexids increase. Consequently, we interpreted the different occlusal morphologies found in the fossil record as different ontogenetic stages, leading to a drastic diminution of latest Miocene-Pliocene taxonomic diversity. The analysis of the geologically oldest capybaras, which are from the Arroyo Chasico Formation (Chasicoan SALMA, late Miocene), is added. This study suggests a single species occurs in this formation that cannot be separated at the genus level from Huayquerian species. In the Arroyo Chasicó species, which is older and theoretically more primitive than that of the Huayquerian, the flexids are shallower as predicted. The analysis supports our model of capybara dental ontogeny and evolution and encourages revision of the whole family according to this model.

Late Miocene capybaras from Argentina: Skull anatomy, taxonomy, evolution, and biochronology

Fossil capybaras are morphologically extremely varied, but previous studies have disagreed on whether this diversity reflects intraspecific variation or the existence of multiple species. Here, we review the capybaras from the classic Argentinian Late Miocene localities of Paraná River cliffs (“conglomerado osífero” of the Ituzaingó Formation, Entre Ríos), and Chillhué and Guatraché shallow lakes (Cerro Azul Formation, La Pampa), and perform a morphometric analysis of their upper cheek teeth and the posterior portion of the rostrum. Our results confirm that all of the specimens from the “conglomerado osífero” belong to the single species Cardiatherium paranense. In addition, we refer a specimen from Tupungato (Río de los Pozos Formation, Mendoza) to C. paranense, thus expanding its geographical range. The material from La Pampa represents a different taxon, and is here preliminary referred to Cardiatherium aff. orientalis. Our systematic interpretation of Late Miocene capybaras suggests that the early radiation of this group was not as explosive as previously thought, and was likely constrained by the early acquisition of large size, increasing complexity of the cheek teeth, and probably semi-aquatic habits.

The First Capybaras (Rodentia, Caviidae, Hydrochoerinae) Involved in the Great American Biotic Interchange

Abstract. The new combination Phugatherium dichroplax nov. comb. (Ahearn and Lance) is proposed for the North American species “Neochoerus” dichroplax Ahearn and Lance, and “N.” cordobai Carranza-Castañeda and Miller. Its age range is here expanded (late Early Blancan—latest Blancan; Piacenzian—Gelasian), being the youngest species of Phugatherium and thus extending the biochron of the genus into the early Pleistocene. This is the first mention of a Pliocene South American lineage of capybaras crossing the Panamanian bridge, implying the recognition of a third lineage of capybaras involved in the Great American Biotic Interchange. The proposed North American origin of the genus Neochoerus is discussed.

Mandibular remains of Procardiomys martinoi Pascual, 1961 (Hystricognathi, Cavioidea) from the Arroyo Chasicó Formation (early late Miocene) of Argentina: anatomy and the phylogenetic position of the genus within Caviidae

Hydrochoerinae is a clade of caviomorph rodents broadly distributed in South America, which includes the maximum body size recorded among extant rodent taxa. The most basal forms of this group are an assemblage of small to medium body size extinct taxa with a plesiomorphic dentition, traditionally clustered in the group cardiomyines. One of the oldest known cardiomyine is Procardiomys martinoi (Chasicoan South American Land Mammal Age SALMA; early late Miocene), which was known only from the holotype, a fragmentary palate with the left and right molar series. New mandibular remains from the Arroyo Chasicó Formation (Chasicoan SALMA) are described and identified here as belonging to P. martinoi because they share a unique combination of characters (as well matching in size) with the upper dentition of the holotype. These materials help in critically reviewing the taxonomic identification of the mandibular remains previously assigned to Procardiomys and allow testing the phylogenetic affinities of this taxon within Caviidae. P. martinoi is depicted as one of the most basal forms of Hydrochoerinae, placed basally on the lineage leading to extant capybaras after the split between the common ancestor of Kerodon and Hydrochoerus. http://zoobank.org/F60356E0-CB8E-48C2-BF86-429E347A9579

The Taxonomic Status of the Pliocene Capybaras (Rodentia) Phugatherium Ameghino and Chapalmatherium Ameghino

Abstract. Living capybaras are a unique group of rodents. They have ever-growing cheek teeth with a complicated occlusal morphology that changes even after birth. Concerning fossil capybaras this morphological change, associated with increasing size, led to regard them as taxonomically highly diverse, including small species with simple dental morphology, and large species with complicated cheek teeth, considered as primitive and derived, respectively. Recently, it was proposed that the different morphs found in each locality actually represent individuals of different ontogenetic stages of a population or successive populations, rather than a multiplicity of coeval species in different stages of evolution. For the Pliocene, the richest locality for capybaras is Farola Monte Hermoso on the southern coast of Buenos Aires Province. This locality yielded four nominal species of capybaras, three of them are a small morph (Phugatherium cataclisticum Ameghino, “Anchimysops villalobosi” Kraglievich, “A. ultra” Kraglievich) and the other a large one (“Chapalmatherium perturbidum” (Ameghino)). In this paper we propose that they represent juveniles and adults of one species, P. cataclisticum. In order to evaluate the phylogenetic position of Phugatherium within Cavioidea a cladistic analysis was performed modifying a previously published combined matrix of morphology and DNA sequences. Phugatherium forms a monophyletic group and is the sister group of modern capybaras. Within Phugatherium the most basal species is P. novum Ameghino, whereas the type species P. cataclisticum is the sister group of P. saavedrai Hoffstetter, Villarroel and Rodrigo.

Paleontology, Evolution and Systematics of Capybara

Caviomorph rodents, the New World Hystricognathi, are one of the most noteworthy groups of mammals in South America. Isolated for more than 30 Ma, they have given rise to several extraordinary rodents including the pacas (Cuniculusspp.), cavies (Caviaspp.), vizcachas (Lagostomusspp.), agouties (Dasyproctaspp.), as well as two giants: Phoberomys, from the late Miocene (6 Ma; mega annum = million years) which probably weighed more than 400 kg (Sanchez Villagra et al. 2003), and Josephoartigasia monesiprobably from the Pleistocene (2.5 Ma), at about 1,000 kg (Rinderknecht and Blanco 2008). Capybaras (Hydrochoerusspp.) are particularly conspicuous because of their size – they are the largest living rodents – and their aggregation in herds (Ojasti 1973; Macdonald 1981; Macdonald et al. 2007). This chapter examines their paleontology and evolution, focusing particularly on another striking feature: their unpaired ever-growing cheek teeth whose very complicated occlusal surface design changes throughout the capybara’s life (Vucetich et al. 2005).

Continental Vertebrates During the Marine Isotope Stage 3 (MIS 3) in Argentina

Paleontological sites in Argentina with continental vertebrates corresponding to the Marine Isotope Stage 3 (MIS 3) interval are scarce or poorly known. This situation is mainly due to the lack of absolute ages for Pleistocene fossil remains or their bearing sediments that would allow the verification of the chronology established for this interval. However, a few isolated evidences show that continental vertebrates responded to the abrupt temperature changes that characterized the MIS 3 (Heinrich colder events and Dansgaard–Oeschger warmer events). Up to date, continental vertebrate remains of this age have been found mainly in Buenos Aires province, but also in a few sites of northeastern Argentina (such as Entre Rios, Corrientes, Formosa and Chaco provinces). In Buenos Aires province: (1) Paso Otero, in the Rio Quequen Grande valley, evidence of warmer and more humid conditions were found in sediments dated in 37,800 ± 2300 radiocarbon years before present (RCYBP); (2) Mar del Sur, General Alvarado County, coastal marine sediments with continental mammals were dated in 25,700 ± 800 and 33,780 ± 1200 RCYBP; (3) Balneario Saldungaray, in the Rio Sauce Grande valley, Tornquist County, gastropods associated with mammal remains were dated in 32,300 ± 1800 and 27,500 ± 670 RCYBP; (4) Los Pozos, Marcos Paz County, sediments dated between 29,000 and 33,000 RCYBP are associated with remains of mammals , birds, reptiles and amphibians; (5) San Pedro, San Pedro County, sediments bearing vertebrate fauna have two OSL datings of 37,626 ± 4198 and 41,554 ± 3756 years B.P. (YBP). In Entre Rios province, Rio Ensenada valley, Diamante Department, some levels of the Tezanos Pinto Formation with OSL datings between 9000 and 35,000 YBP yielded remains of grazer megamammals and other taxa characteristic of the modern Patagonian Domain. In the province of Corrientes, Arroyo Toropi, Bella Vista, vertebrate remains dated with OSL from 36,000 to 52,000 YBP show a clear taxonomic change in response to climatic fluctuations. In Formosa province, Rio Bermejo, Villa Escolar sediments of the Fortin Tres Pozos Formation, bearing vertebrate fauna have an OSL age of 58,160 ± 4390 YBP. In the province of Chaco, Charata locality, gastropods associated with mammal remains were dated between 22,000 and 27,000 RCYBP. A larger amount of absolute datings of the bearing sediments and especially taxon dates are needed to determine more accurately the response of the fauna to the climate changes characteristic of MIS 3.

Marine Isotope Stage 3 in Southern South America, 60 KA B.P.-30 KA B.P.

This volume was conceived during the Symposium “El Estadio Isotópico 3 en la Argentina y el sur de América del Sur: 60.000 a 25.000 años atrás” (The Marine Isotope Stage 3 (MIS 3) in Argentina and southern South America: 60,000 to 25,000 years ago) held in June 2013, in La Plata, Argentina. The main purpose of this meeting was to promote the interaction of the leading scientists in various disciplines of the Geological and Paleontological Sciences of the Late Cenozoic of South America in order to update the existing knowledge on the core issues cited in the title of the symposium (e.g., geology, geomorphology, vertebrate and invertebrate paleontology, palynology, paleomagnetism, paleoenvironmental and paleoclimatic studies, etc). This was the first time ever that these topics related to MIS 3 were publicly discussed in Argentina. The Quaternary geological history is characterized by cyclical climatic changes (glacial and intervals). These cyclical changes generated periodic reorganizations of the landscape and the environmental system. MIS 3 was an interstadial stage, a relatively warmer climatic period which G.M. Gasparini C. Deschamps División Paleontologia Vertebrados, Museo de La Plata, Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, La Plata 1900, Buenos Aires, Argentina e-mail: ceci@fcnym.unlp.edu.ar J. Rabassa Laboratorio de Geomorfología y Cuaternario, CADIC-CONICET, Universidad Nacional de Tierra del Fuego, Ushuaia 9410, Tierra del Fuego, Argentina e-mail: jrabassa@gmail.com E.P. Tonni Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, La Plata 1900, Buenos Aires, Argentina e-mail: eptonni@fcnym.unlp.edu.ar G.M. Gasparini (&) J. Rabassa Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina e-mail: germanmgasparini@gmail.com C. Deschamps Comisión de Investigaciones Científicas (CIC), La Plata, Buenos Aires, Argentina