Rhynchosaurs are a clade of robust, quadruped, and herbivorous stem-archosauromorph diapsids restricted to the Triassic Period. Most species have a specialized masticatory apparatus composed of a blade-and-groove occlusion and multiple longitudinal tooth rows. Rhynchosaurs are the most numerically abundant tetrapods of the Upper Triassic Ischigualasto Formation of NW Argentina. However, there is currently a single nominal species, Hyperodapedon sanjuanensis, described for this unit and the entire country. Though the dental morphology constitutes one of the most important sources of taxonomic and phylogenetic information of the group, this anatomical region remains undescribed in the holotype of Hyperodapedon sanjuanensis. The full occlusion of the skull and lower jaw obscures most of the morphology of the masticatory apparatus in this specimen. Here we present the first description of the maxillary tooth plate and dentary dentition of this specimen based on CT scan data and a three-dimensional rendering. The maxillary tooth plate of the holotype of Hyperodapedon sanjuanensis possesses two tooth-bearing areas that are separated by a single longitudinal groove. The lateral tooth-bearing area of the maxilla is wider than the medial one. The dentary possesses a single cutting blade and tooth row. Both maxilla and dentary lack lingual dentition. The information gathered here was used to emend the diagnosis of the species, review the taxonomy of some specimens, and check the dental scorings for Hyperodapedon sanjuanensis—based on the morphology of the holotype—in three independent phylogenetic data sets.

Proterotheriidae constitute a group of small-medium native South American ungulates with high diversity during the early Miocene and the late Miocene (Santacrucian and Huayquerian SALMAs). Recent studies demonstrated the wide dental variability, useful in the discrimination of the species. The aim of this work is to analyze the humerus as a postcranial element that is usually not found in association with cranial remains, and to evaluate (qualitatively and quantitatively) its systematic usefulness. We used the only known specimen of “Proterotherium berroi”, re-describing and re-illustrating it. The Principal Components Analysis resulted in 2 components explaining 86% of the variance. The PCA showed a differentiation between the largest species—Diadiaphorus majusculus and Anisolophus floweri—and the remaining ones (an intermediate group consisting of “Proterotherium”, Tetramerorhinus, Eoauchenia, Proterotheriidae indet., and the smallest, Thoatherium minusculum). We establish that, although there are slight morphological differences in the distal epiphysis of the humeri of Proterotheriidae, they mostly correspond to gradual changes in characters with continuous variations not linked to any particular taxonomic entity. These are not enough to assure a generic or specific determination, except for Eoauchenia. The differences in humeri size are considerable and they could be used as a criterion for discriminating Diadiaphorus and Anisolophus, to which the largest specimens would belong. We consider “P. berroi” a probable synonym of Neolicaphrium recens, but we ratify that a reliable systematic determination is only possible if it is based on cranial or dental remains.

In this study, we record and describe fossil sigmodontine rodents from the Gruta do Urso cave in the municipality of Aurora do Tocantins, Tocantins state, Northern Brazil. The sediments bearing fossils were deposited during the time spanning between 22,000 years before present (YBP) and 3,800 YBP, corresponding to the Late Pleistocene to Middle Holocene. The fossil specimens consist mostly of isolated molars and some fragments of maxillae and mandibles. We identified 12 sigmodontine taxa: Akodon sp. 1, Akodon sp. 2, Calomys sp., Holochilus sp., Kunsia tomentosus, Necromys lasiurus, Oecomys sp., Oligoryzomys sp. 1, Oligoryzomys cf. mattogrossae, Oxymycterus sp., Pseudoryzomys simplex, and Thalpomys lasiotis. This is the first fossil record for the group in Northern Brazil, and one of the largest assemblages of Pleistocene-Holocene sigmodontines registered in a single cave in the Neotropical region. Based on the diversity of the sigmodontine rodents presented herein, and on the associated fauna previously recorded from the same cave, we reconstructed the Late Pleistocene paleoenvironmental conditions of the region, similar to those of the present, as an area dominated by open vegetation formations with gallery forest patches.

This work describes the composition and distribution of sclerobionts on the Miocene Patagonian oyster Ostrea alvarezii d'Orbigny and provides information about its paleoenvironment. The structure of sclerobiont assemblages and their preferential distribution on left/right valves (n=340) as well as their external/internal surfaces and areas was evaluated by means of multivariate analyses (nMDS, SIMPER), non-parametric tests for producing mean comparisons, and goodness of fit tests using coverage and abundance data. Sixteen ichnotaxa were recorded. Bivalves, polychaetes and bryozoans were the most representative encrusters. External surfaces, left valves and sediment-free areas were the most colonized. O. alvarezii beds are interpreted as within-habitat time-averaged assemblages. Oysters appear to have lived in small subtidal channels in a low energy tidal flat and closely related to the sediment-water interface, with the right valve resting on the substrate. Sclerobionts showed diverse behaviors, trophic levels and tiering. This suggests that sclerobiont assemblages on O. alvarezii had a complex structure with subdivision of resources, including a vertical colonization of valves by tracemakers at different levels of depth.

From the analysis of the taphonomic attributes of the specimens of Heleobia parchappii found in fluvial and paleolacustrine sequences of the lower basin of the Salado River, the surface alteration of their shells was comparatively studied in order to assess the differences between both environments. The main results that were obtained by means of Non-Metric Multidimensional Scaling (NMDS) and analysis of similarity (ANOSIM) tests (R=0.31, p<0.01) enabled the recognition and statistical differentiation of both groups of samples. The taphonomic characteristics presented by those that were recovered from the paleolacustrine environment are more similar to each other, whereas those from the fluvial environment showed greater dispersion. Through the similarity percentage (SIMPER) analysis we could determine that the variables of discoloration and dissolution were the most important features to differentiate both groups, and that the values of the indexes (Total Taphonomic Grades) were always higher in the paleolacustrine assemblages, thus showing greater decay. The differences of preservation could be explained by the residence time of the remains near the water-sediment interface as well as by the differences in the sedimentation rate in both environments, which control the different exposure cycles of the shells. These differences would be related to changes in the hydrological regime (fluctuations in surface and groundwater levels) that, although affecting the entire study area, are more intense and frequent in shallow lakes, therefore favoring the decay of the shells accumulated in this environment.