Adaptive diversity of incisor enamel microstructure in South American burrowing rodents (family Ctenomyidae, Caviomorpha)

The aim of this study was to analyse the morphofunctional and adaptive significance of variation in the upper incisor enamel microstructure of South American burrowing ctenomyids and other octodontoid taxa. We studied the specialized subterranean tooth-digger †Eucelophorus chapalmalensis (Pliocene - Middle Pleistocene), and compared it with other fossil and living ctenomyids with disparate digging adaptations, two fossorial octodontids and one arboreal echimyid. Morphofunctionally significant enamel traits were quite similar among the species studied despite their marked differences in habits, digging behaviour and substrates occupied, suggesting a possible phylogenetic constraint for the Octodontoidea. In this context of relative similarity, the inclination of Hunter-Schreger bands, relative thickness of external index (EI) and prismless enamel zone were highest in †Eucelophorus, in agreement with its outstanding craniomandibular tooth-digging specialization. Higher inclination of Hunter-Schreger bands reinforces enamel to withstand high tension forces, while high external index provides greater resistance to wear. Results suggest increased frequency of incisor use for digging in †Eucelophorus, which could be related to a more extreme tooth-digging strategy and/or occupancy of hard soils. Higher external index values as recurring patterns in distant clades of tooth-digging rodents support an adaptive significance of this enamel trait.Facultad de Ciencias Naturales y Muse

Évolution dentaire chez les Neophanomys (Rodentia, Octodontidae) du Miocène tardif d’Argentine centrale

The evolutionary pattern of the molar morphology of the small caviomorph (Octodontidae) Neophanomys from the late Miocene Cerro AzulFormation of central Argentina is analyzed. Two new species (chronomorphs) are recognized, which constitute an anagenetically evolving lineagewith a gradual and directional pattern of increasing molar hypsodonty. Dental changes related to increasing hypsodonty are comparable to those ofthe octodontid lineage Chasichimys also recovered from the Cerro Azul Formation. However, Neophanomys shows comparatively less variation ingross morphology and there are no evidences that this lineage achieved euhypsodonty. In contrast, important changes in enamel microstructure(schmelzmuster) are observed among different populations of Neophanomys, supporting the hypothesis that these changes can occur at leastpartially independently from modifications in dental gross morphology. The patterns of dental evolution detected in the Neophanomys andChasichimys-Xenodontomys lineages and the unequivocal polarity of the changes involved, related to increasing hypsodonty, reinforce thehypothesis that chronological differences exist among late Miocene outcroppings of Cerro Azul Formation in central Argentina.Fil: Verzi, Diego Hector. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Zoología de Vertebrados. Sección de Mastozoología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; ArgentinaFil: Vieytes, Emma Carolina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Zoología de Vertebrados. Sección de Mastozoología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; ArgentinaFil: Montalvo, Claudia Inés. Universidad Nacional de La Pampa; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

† Estelestes ensis (Mammalia, Metatheria) from the early Eocene of Baja California (Mexico) as a generalized polydolopimorphian

Estelestes ensis Novaceck et al., 1991 is a curious Paleogene metatherian mammal recognized on the basis of a single specimen from Baja California (Mexico) in southern North America. It comes from early Eocene (Wasatchian age) levels of the Las Tetas de Cabra Formation at “Marsupial Hill” in the Lomas Las Tetas de Cabra site (also known as Punta Prieta; see Novaceck et al., 1991). The specimen consists of a fragmentary left mandible with the last premolar, the roots of the first two molars, and almost complete last two molars (Fig. 1). It was referred to the Didelphini (Marsupialia, Didelphimorphia, Didelphidae, Didelphinae) even though Novaceck et al. (1991) stated that the overall morphology of the type specimen poses intriguing problems regarding its relationships. For example, the very deep, robust jaw of Estelestes distinguishes it from any other Holarctic “didelphine” (at the time Novaceck et al., 1991 published their work, both the concept and extent of Didelphidae and Didelphinae were much broader than today). Interestingly, they concluded that Estelestes had close affinities with “Mirandotherium” (lapsus calami for Mirandatherium), from the early Eocene of Itaboraí, in southeastern Brazil. “Resemblance between the two taxa is nevertheless striking, once again raising the possibility of close relationships among certain early members of the Northern Hemisphere and South American Didelphinae” (Novaceck et al., 1991, p. 16). The affinities of Mirandatherium are contested, having been regarded as part of the Didelphimorphia (e.g., de Paula Couto, 1952a) or Microbiotheria (e.g., Marshall, 1987; McKenna and Bell, 1997; Oliveira and Goin, 2011), or even as an alphadontian (Carneiro, 2019).Fil: Goin, Francisco Javier. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; ArgentinaFil: Vieytes, Emma Carolina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; ArgentinaFil: Crespo Roures, Vicente Daniel. Universidade Nova de Lisboa; Portugal. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; ArgentinaFil: Oliveira, Édison V.. Universidade Federal de Pernambuco; Brasi

Adaptive diversity of incisor enamel microstructure in South American burrowing rodents (family Ctenomyidae, Caviomorpha)

The aim of this study was to analyse the morphofunctional and adaptive significance of variation in the upper incisor enamel microstructure of South American burrowing ctenomyids and other octodontoid taxa. We studied the specialized subterranean tooth-digger †Eucelophorus chapalmalensis (Pliocene - Middle Pleistocene), and compared it with other fossil and living ctenomyids with disparate digging adaptations, two fossorial octodontids and one arboreal echimyid. Morphofunctionally significant enamel traits were quite similar among the species studied despite their marked differences in habits, digging behaviour and substrates occupied, suggesting a possible phylogenetic constraint for the Octodontoidea. In this context of relative similarity, the inclination of Hunter-Schreger bands, relative thickness of external index (EI) and prismless enamel zone were highest in †Eucelophorus, in agreement with its outstanding craniomandibular tooth-digging specialization. Higher inclination of Hunter-Schreger bands reinforces enamel to withstand high tension forces, while high external index provides greater resistance to wear. Results suggest increased frequency of incisor use for digging in †Eucelophorus, which could be related to a more extreme tooth-digging strategy and/or occupancy of hard soils. Higher external index values as recurring patterns in distant clades of tooth-digging rodents support an adaptive significance of this enamel trait.Facultad de Ciencias Naturales y Muse

A brief history of caviomorph rodents as told by the fossil record

Fil: Vucetich, María Guiomar. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología VertebradosFil: Arnal, Michelle. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología VertebradosFil: Deschamps, Cecilia Marcela. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología VertebradosFil: Pérez, María Encarnación. Museo Paleontológico Egidio Feruglio. Trelew; ArgentinaFil: Vieytes, Emma Carolina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Mastozoologí

First record of Cardiatherium chasicoense (Rodentia, Hydrochoeridae) out of the pampeana region (Argentina) and its biostratigraphical significance

Se estudia un resto de paladar y mandíbula asociados, de un roedor procedente del Miembro Arenisca Albardón de la Formación Loma de las Tapias, provincia de San Juan. El resto se asigna a Cardiatherium chasicoense (Hydrochoeridae) y constituye el único material de la especie hallado fuera de la región pampeana y de su localidad tipo, Arroyo Chasicó, provincia de Buenos Aires. Dicho ejemplar representa el único resto conocido de cráneo asociado a mandíbula para esta especie, hecho que permite corroborar la asignación a C. chasicoense de molariformes superiores aislados procedentes de la localidad tipo. El nuevo ejemplar se incluyó en estudios cuantitativos con todas las especies de Cardiatherium reconocidas, y en métodos de morfometría geométrica para comparar rasgos anatómicos que no pudieron ser evaluados mediante medidas lineares. Dicho ejemplar corresponde a un individuo juvenil, que se ajustó a la propuesta de crecimiento ontogenético para los carpinchos del Mioceno tardío. Su asignación a C. chasicosense sugiere una edad Chasiquense, en concordancia con una datación de la sección media de la Arenisca Albardón de 7.0 + 0.9 Ma. Los sedimentos portadores fueron depositados por un río entrelazado, igual que todos los registros de carpinchos fósiles, hallados hasta el momento. Esto se corresponde con los hábitos semiacuáticos de los representantes actuales de la familia.A skull and associated mandible of a rodent found in the Arenisca Albardón Member, Loma de las Tapias Formation, San Juan Province,Argentina, is studied. It is assigned to the species Cardiatherium chasicoense (Hydrochoeridae), being the single record of this species out of its type locality, Arroyo Chasicó, Buenos Aires province. In addition, this is the single remain with skull and mandible in association, which permits corroboration of the assignment to this species of isolated upper teeth found in the type locality. This specimen was compared qualitatively with all the species of Cardiatherium so far recognized, and was included in geometric morphometric analyses in order to compare morphological features that could not be evaluated through linear measurements. The specimen is a juvenile, and proved to fit within the model proposed for ontogenetic growing of cheek teeth for late Miocene capybaras. Its assignment to C. chasicoense permits the correlation of the bearing levels with those of the type locality, lithofacies association 3 (Las Barrancas Member) of the Arroyo Chasicó Formation, suggesting an age of ca. 7 Ma for these latter, on the basis of a dating of the middle section of the Arenisca Albardón Member which yielded 7.0 + 0.9 Ma. The bearing sediments are interpreted as deposited by a braided river. So far, all the records of fossil capybaras have been found in water-related sediments, in accordance with the semiaquatic habits of their modern representatives.Facultad de Ciencias Naturales y MuseoComisión de Investigaciones Científicas de la provincia de Buenos AiresConsejo Nacional de Investigaciones Científicas y Técnica

First record of Cardiatherium chasicoense (Rodentia, Hydrochoeridae) out of the pampeana region (Argentina) and its biostratigraphical significance

Se estudia un resto de paladar y mandíbula asociados, de un roedor procedente del Miembro Arenisca Albardón de la Formación Loma de las Tapias, provincia de San Juan. El resto se asigna a Cardiatherium chasicoense (Hydrochoeridae) y constituye el único material de la especie hallado fuera de la región pampeana y de su localidad tipo, Arroyo Chasicó, provincia de Buenos Aires. Dicho ejemplar representa el único resto conocido de cráneo asociado a mandíbula para esta especie, hecho que permite corroborar la asignación a C. chasicoense de molariformes superiores aislados procedentes de la localidad tipo. El nuevo ejemplar se incluyó en estudios cuantitativos con todas las especies de Cardiatherium reconocidas, y en métodos de morfometría geométrica para comparar rasgos anatómicos que no pudieron ser evaluados mediante medidas lineares. Dicho ejemplar corresponde a un individuo juvenil, que se ajustó a la propuesta de crecimiento ontogenético para los carpinchos del Mioceno tardío. Su asignación a C. chasicosense sugiere una edad Chasiquense, en concordancia con una datación de la sección media de la Arenisca Albardón de 7.0 + 0.9 Ma. Los sedimentos portadores fueron depositados por un río entrelazado, igual que todos los registros de carpinchos fósiles, hallados hasta el momento. Esto se corresponde con los hábitos semiacuáticos de los representantes actuales de la familia.A skull and associated mandible of a rodent found in the Arenisca Albardón Member, Loma de las Tapias Formation, San Juan Province,Argentina, is studied. It is assigned to the species Cardiatherium chasicoense (Hydrochoeridae), being the single record of this species out of its type locality, Arroyo Chasicó, Buenos Aires province. In addition, this is the single remain with skull and mandible in association, which permits corroboration of the assignment to this species of isolated upper teeth found in the type locality. This specimen was compared qualitatively with all the species of Cardiatherium so far recognized, and was included in geometric morphometric analyses in order to compare morphological features that could not be evaluated through linear measurements. The specimen is a juvenile, and proved to fit within the model proposed for ontogenetic growing of cheek teeth for late Miocene capybaras. Its assignment to C. chasicoense permits the correlation of the bearing levels with those of the type locality, lithofacies association 3 (Las Barrancas Member) of the Arroyo Chasicó Formation, suggesting an age of ca. 7 Ma for these latter, on the basis of a dating of the middle section of the Arenisca Albardón Member which yielded 7.0 + 0.9 Ma. The bearing sediments are interpreted as deposited by a braided river. So far, all the records of fossil capybaras have been found in water-related sediments, in accordance with the semiaquatic habits of their modern representatives.Facultad de Ciencias Naturales y MuseoComisión de Investigaciones Científicas de la provincia de Buenos AiresConsejo Nacional de Investigaciones Científicas y Técnica

First record of Cardiatherium chasicoense (Rodentia, Hydrochoeridae) out of the pampeana region (Argentina) and its biostratigraphical significance

Se estudia un resto de paladar y mandíbula asociados, de un roedor procedente del Miembro Arenisca Albardón de la Formación Loma de las Tapias, provincia de San Juan. El resto se asigna a Cardiatherium chasicoense (Hydrochoeridae) y constituye el único material de la especie hallado fuera de la región pampeana y de su localidad tipo, Arroyo Chasicó, provincia de Buenos Aires. Dicho ejemplar representa el único resto conocido de cráneo asociado a mandíbula para esta especie, hecho que permite corroborar la asignación a C. chasicoense de molariformes superiores aislados procedentes de la localidad tipo. El nuevo ejemplar se incluyó en estudios cuantitativos con todas las especies de Cardiatherium reconocidas, y en métodos de morfometría geométrica para comparar rasgos anatómicos que no pudieron ser evaluados mediante medidas lineares. Dicho ejemplar corresponde a un individuo juvenil, que se ajustó a la propuesta de crecimiento ontogenético para los carpinchos del Mioceno tardío. Su asignación a C. chasicosense sugiere una edad Chasiquense, en concordancia con una datación de la sección media de la Arenisca Albardón de 7.0 + 0.9 Ma. Los sedimentos portadores fueron depositados por un río entrelazado, igual que todos los registros de carpinchos fósiles, hallados hasta el momento. Esto se corresponde con los hábitos semiacuáticos de los representantes actuales de la familia.A skull and associated mandible of a rodent found in the Arenisca Albardón Member, Loma de las Tapias Formation, San Juan Province,Argentina, is studied. It is assigned to the species Cardiatherium chasicoense (Hydrochoeridae), being the single record of this species out of its type locality, Arroyo Chasicó, Buenos Aires province. In addition, this is the single remain with skull and mandible in association, which permits corroboration of the assignment to this species of isolated upper teeth found in the type locality. This specimen was compared qualitatively with all the species of Cardiatherium so far recognized, and was included in geometric morphometric analyses in order to compare morphological features that could not be evaluated through linear measurements. The specimen is a juvenile, and proved to fit within the model proposed for ontogenetic growing of cheek teeth for late Miocene capybaras. Its assignment to C. chasicoense permits the correlation of the bearing levels with those of the type locality, lithofacies association 3 (Las Barrancas Member) of the Arroyo Chasicó Formation, suggesting an age of ca. 7 Ma for these latter, on the basis of a dating of the middle section of the Arenisca Albardón Member which yielded 7.0 + 0.9 Ma. The bearing sediments are interpreted as deposited by a braided river. So far, all the records of fossil capybaras have been found in water-related sediments, in accordance with the semiaquatic habits of their modern representatives.Facultad de Ciencias Naturales y MuseoComisión de Investigaciones Científicas de la provincia de Buenos AiresConsejo Nacional de Investigaciones Científicas y Técnica

A Late Cretaceous mammal from Brazil and the first radioisotopic age for the Bauru Group

In the last three decades, records of tribosphenidan mammals from India, continental Africa, Madagascar and South America have challenged the notion of a strictly Laurasian distribution of the group during the Cretaceous. Here, we describe a lower premolar from the Late Cretaceous Adamantina Formation, SãoPaulo State, Brazil. It differs from all known fossil mammals, except for a putative eutherian from the same geologic unity and Deccanolestes hislopi, from the Maastrichtian of India. The incompleteness of the material precludes narrowing down its taxonomic attribution further than Tribosphenida, butit is larger than most coeval mammals and shows a thin layer of parallel crystallite enamel. The new taxon helps filling two major gaps in the fossil record: the paucity of Mesozoic mammals in more northern parts of South Americaand of tribosphenidans in the Cretaceous of that continent. In addition, high-precision U-Pb geochronology provided a post-Turonian maximal age (≤87.8 Ma) for the type stratum, which is overlain by the dinosaur-bearing Marília Formation, constraining the age of the Adamantina Formation at the site to late Coniacian?late Maastrichtian. This represents the first radioisotopic age for the Bauru Group, a key stratigraphic unit for the study of Cretaceous tetrapods in Gondwana.Fil: Castro, Mariela. Universidade de Sao Paulo; BrasilFil: Goin, Francisco Javier. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; ArgentinaFil: Ortiz Jaureguizar, Edgardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; ArgentinaFil: Vieytes, Emma Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Zoología de Vertebrados; ArgentinaFil: Tsukui, Kaori. Massachusetts Institute of Technology; Estados UnidosFil: Ramezani, Jahandar. Massachusetts Institute of Technology; Estados UnidosFil: Batezelli, Alessandro. Universidade Estadual de Campinas; BrasilFil: Marsola, Julio. Universidade de Sao Paulo; BrasilFil: Langer, Max. Universidade de Sao Paulo; Brasi

New Metatherian Mammal from the Early Eocene of Antarctica

A new Paleogene metatherian from locality IAA 1/90, Marambio (Seymour) Island in the Antarctic Peninsula is described. Pujatodon ektopos, gen. et sp. nov., is recognized on the basis of a tiny lower left molar recovered from early Eocene (late Ypresian) levels of the Cucullaea I Allomember, La Meseta Formation. The tooth is characterized by its small size, bunoid aspect, short trigonid with closely set paraconid and metaconid, wide and long talonid, the development of an incipient cingulid at the labial base of the crown between the trigonid and talonid, and an expanded posterior cingulid. Body mass estimations for the new taxon range from 83.13 to 153.15 g. Its enamel microstructure shows the earliest evidence among metatherians of aligned prisms, as well as of interprismatic sheets of matrix. The analysis of other parameters, like body mass, molar morphometric index, and wear facets, suggests that the molars of Pujatodon were primarily adapted to the processing of fruits, nuts, seeds, and/or hard insects. Several features suggest the allocation of this specimen among basal polydolopimorphians (Prepidolopidae or, more probably, Glasbiidae). The discovery of the specimen MLP 14-I-10-20 could offer new insights on the origins and early diversification of Australidelphian marsupials in southern (and northern?) continents. It also adds significant information on the diversity of Antarctic Paleogene mammals, their evolution, habits, and historical biogeography.Facultad de Ciencias Naturales y Muse