Pleistocene South American native ungulates (Notoungulata and Litopterna) of the historical Roth collections in Switzerland, from the Pampean Region of Argentina.

The fossil collections made by early explorers in South America have been fundamental to reveal the past diversity of extinct mammals and unravel their evolutionary history. One important early explorer in South America was the Swiss-Argentine palaeontologist Kaspar Jacob Roth, known as Santiago Roth (1850, Herisau, Switzerland-1924, Buenos Aires, Argentina), who made significant collections of fossil mammals that are housed in museums in Europe and Argentina. The important collections of Roth in Switzerland include iconic Pleistocene megafauna from the Pampean Region (Argentina). The palaeontological significance of the Pampean Region relies on its abundant record of fossil vertebrates that documents diversity dynamics and paleoenvironmental change in southern South America, serving as the basis for the South American biostratigraphical scale of the late Neogene and Quaternary. The South American native ungulates (SANUs) were hoofed placental mammals that radiated in South America. The clades Notoungulata and Litopterna include, among others, the last representatives of SANUs megafauna in the continent. We revise and describe for the first time the SANUs specimens from the Pampean Region of the Roth collections in Switzerland. The collections include two species of notoungulates (Toxodon cf. T. platensis and Mesotherium cristatum) and one litoptern species (Macrauchenia patachonica). The occurrences are restricted to the early and middle Pleistocene (pre-Lujanian Stages/Ages). Although the SANUs diversity in the Roth collections is low in comparison with other groups (e.g., xenarthrans), some of the specimens are very complete, including skulls and postcranial remains. The completeness of the Ma. patachonica material allows an update and reinterpretation of some of the details of the dentition and the postcranial skeleton of this iconic species. In addition to its historical importance, the SANU specimens from the Roth collections provide important information to study the paleobiology and evolution of South American megafauna and evaluate hypotheses about their extinction in the continent.

Las colecciones de fósiles realizadas por los primeros exploradores en América del Sur han sido fundamentales para revelar la diversidad pasada de los mamíferos sudamericanos y desentrañar su historia evolutiva. Un importante explorador en América del Sur fue el paleontólogo suizo-argentino Kaspar Jacob Roth, conocido como Santiago Roth (1850, Herisau, Suiza-1924, Buenos Aires, Argentina), quien realizó importantes colecciones de mamíferos fósiles que se encuentran en museos de Europa y Argentina. Las colecciones de Roth en Suiza incluyen la icónica megafauna del Pleistoceno de la Región Pampeana (Argentina). La importancia paleontológica de la Región Pampeana se basa en su abundante registro de vertebrados fósiles que documenta la diversidad y el cambio paleoambiental en el sur de Sudamérica, sirviendo como base para la escala bioestratigráfica sudamericana del Neógeno tardío y Cuaternario. Los ungulados nativos sudamericanos (SANUs, por sus siglas en inglés) eran mamíferos placentarios con pezuñas que radiaron en Sudamérica. Los clados Notoungulata y Litopterna incluyen, entre otros, los últimos representantes de la megafauna de SANUs en el continente. En este trabajo, revisamos y describimos por primera vez los SANUs de la Región Pampeana de las colecciónes de Roth en Suiza. Las colecciónes incluyen dos especies de notungulados (Toxodon cf. T. platensis y Mesotherium cristatum) y una especie de litopterna (Macrauchenia patachonica). Las ocurrencias están restringidas al Pleistoceno temprano y medio (Pisos/Edades anteriores al Lujanense). Aunque la diversidad de SANU en las colecciónes Roth es baja en comparación con otros grupos (por ejemplo, xenarthros), algunos de los especímenes son muy completos, e incluyen cráneos y restos poscraneales. Lo completo del material de Ma. patachonica permite una actualización y reinterpretación de algunos de los detalles de la dentición y el esqueleto poscraneal de esta icónica especie. Además de su importancia histórica, los SANUs de la colección Roth brindan información importante para estudiar la paleobiología y evolución de la megafauna sudamericana y evaluar hipótesis sobre su extinción en el continente.

Relict duck-billed dinosaurs survived into the last age of the dinosaurs in subantarctic Chile.

In the dusk of the Mesozoic, advanced duck-billed dinosaurs (Hadrosauridae) were so successful that they likely outcompeted other herbivores, contributing to declines in dinosaur diversity. From Laurasia, hadrosaurids dispersed widely, colonizing Africa, South America, and, allegedly, Antarctica. Here, we present the first species of a duck-billed dinosaur from a subantarctic region, Gonkoken nanoi, of early Maastrichtian age in Magallanes, Chile. Unlike duckbills further north in Patagonia, Gonkoken descends from North American forms diverging shortly before the origin of Hadrosauridae. However, at the time, non-hadrosaurids in North America had become replaced by hadrosaurids. We propose that the ancestors of Gonkoken arrived earlier in South America and reached further south, into regions where hadrosaurids never arrived: All alleged subantarctic and Antarctic remains of hadrosaurids could belong to non-hadrosaurid duckbills like Gonkoken. Dinosaur faunas of the world underwent qualitatively different changes before the Cretaceous-Paleogene asteroid impact, which should be considered when discussing their possible vulnerability.

Brawn before brains in placental mammals after the end-Cretaceous extinction.

Mammals are the most encephalized vertebrates, with the largest brains relative to body size. Placental mammals have particularly enlarged brains, with expanded neocortices for sensory integration, the origins of which are unclear. We used computed tomography scans of newly discovered Paleocene fossils to show that contrary to the convention that mammal brains have steadily enlarged over time, early placentals initially decreased their relative brain sizes because body mass increased at a faster rate. Later in the Eocene, multiple crown lineages independently acquired highly encephalized brains through marked growth in sensory regions. We argue that the placental radiation initially emphasized increases in body size as extinction survivors filled vacant niches. Brains eventually became larger as ecosystems saturated and competition intensified.

Divergence-time estimates for hominins provide insight into encephalization and body mass trends in human evolution.

Quantifying speciation times during human evolution is fundamental as it provides a timescale to test for the correlation between key evolutionary transitions and extrinsic factors such as climatic or environmental change. Here, we applied a total evidence dating approach to a hominin phylogeny to estimate divergence times under different topological hypotheses. The time-scaled phylogenies were subsequently used to perform ancestral state reconstructions of body mass and phylogenetic encephalization quotient (PEQ). Our divergence-time estimates are consistent with other recent studies that analysed extant species. We show that the origin of the genus Homo probably occurred between 4.30 and 2.56 million years ago. The ancestral state reconstructions show a general trend towards a smaller body mass before the emergence of Homo, followed by a trend towards a greater body mass. PEQ estimations display a general trend of gradual but accelerating encephalization evolution. The obtained results provide a rigorous temporal framework for human evolution.

The impact of locomotion on the brain evolution of squirrels and close relatives.

How do brain size and proportions relate to ecology and evolutionary history? Here, we use virtual endocasts from 38 extinct and extant rodent species spanning 50+ million years of evolution to assess the impact of locomotion, body mass, and phylogeny on the size of the brain, olfactory bulbs, petrosal lobules, and neocortex. We find that body mass and phylogeny are highly correlated with relative brain and brain component size, and that locomotion strongly influences brain, petrosal lobule, and neocortical sizes. Notably, species living in trees have greater relative overall brain, petrosal lobule, and neocortical sizes compared to other locomotor categories, especially fossorial taxa. Across millions of years of Eocene-Recent environmental change, arboreality played a major role in the early evolution of squirrels and closely related aplodontiids, promoting the expansion of the neocortex and petrosal lobules. Fossoriality in aplodontiids had an opposing effect by reducing the need for large brains.