Karina Buldrini Oviedo

The early Oligocene Tinguiririca Fauna from the Abanico Formation, central Chile, is the earliest mammal fauna dominated by high-crowned (hypsodont) herbivores known globally. The drivers of early hypsodonty in South America are thus of considerable interest. We reconstruct the palaeoenvironment for Tinguiririca based on: (1) generalised linear latent variable models (GLLVMs), which compare body mass distributions of Tinguirirican and modern South American herbivores; and (2) reconstructed diets of Tinguiririca fauna notoungulates inferred from dental mesowear. Based on GLLVMs, the Tinguiririca Fauna’s palaeoenvironment is interpreted as relatively warm (22˚C mean annual temperature), dry (1200 mm yr ^-1 mean annual precipitation) and open (23% tree cover). The Brazilian Caatinga is the closest modern South American analogue to the dry, low-vegetation-density palaeoenvironment inferred for Tinguiririca. We interpret the fauna’s notoungulates as browsers, based on their sharp ectoloph wear facets. To test this interpretation, we also analysed the mesowear angles and relative crown heights of a broad array of leontiniid and homalodotheriid notoungulates, two clades specialised for high browsing that never attained the levels of hypsodonty seen in other notoungulates. Both have sharp mesowear and greater relative crown heights than modern high browsers. Our data suggest that neither gradual habitat change nor increased levels of volcaniclastic sedimentation alone caused the early attainment of hypsodonty in notoungulates. Alternative explanations, such as one or more rapid pulses of environmental change driving the increase in hypsodonty or the unique taxonomic composition of South American faunas, must be invoked to explain the marked increase in crown height from preceding time periods into the Tinguirirican South American Land Mammal Age.

The vomeronasal system (VNS) has been extensively associated with the regulation of sexual and social behaviors in mammals. This system comprises two types of vomeronasal neurons sending parallel projections from the vomeronasal organ (VNO) to the anterior and posterior portions of the accessory olfactory bulb (aAOB and pAOB, respectively). Members of caviomorph rodents develop either a larger aAOB or pAOB bias, which has been associated with ecological traits related to the pheromonal communication displayed by these species. However, it is still unknown how and when such AOB asymmetries emerge and whether experience may influence their establishment. To explore these factors, we studied the development of the VNS in Octodon degus, a caviomorph that exhibits an asymmetric AOB, in which the aAOB is larger and has more glomeruli than the pAOB. We found that both VNO and AOB are present at birth, but exhibiting substantial immature traits. Both VNS structures develop postnatally, showing mature patterns by the end of the first postnatal month. By the second postnatal week, aAOB becomes larger in size than pAOB, however, in the glomerular layer such bias appears later, by the end of the first postnatal month. The AOB asymmetry increases in extent until adulthood, as in this period the pAOB shows a minor growing rate than the aAOB. Additionally, we found that animals raised in restricted social contexts displayed a reduced AOB asymmetry in comparison to wild degus. Overall, we suggest that social experiences contribute to the development of the AOB asymmetry in degus.

In this study, new isolated fragmentary pterosaur bones are described from Lower Cretaceous outcrops exposed at Cerro La Isla, a site located approximately 95 km east of Copiapó city, Atacama region, northern Chile. The material consists of a jaw fragment with broken teeth, the caudal portion of a mid-cervical vertebra and the distal portion of a femur. Based on their morphology, the jaw and cervical fragments are assigned to Ctenochasmatidae, a group of pterodactyloid pterosaurs that has been previously reported from this locality, while the femur lacks diagnostic characters that would allow its referral to a more exclusive taxon than Pterodactyloidea indet. This new material confirms the previously proposed presence of ctenochasmatid pterosaurs in the Cretaceous outcrops of Cerro La Isla, and increases the diversity of their skeletal elements discovered at the site.