Darin A. Croft

The Tinguiririca Fauna, Chile: Biochronology, paleoecology, biogeography, and a new earliest Oligocene South American Land Mammal 'Age'

Abstract A new South American Land Mammal ‘Age’ (SALMA), the Tinguirirican, is formally established, based on an assemblage of at least 25 taxa from the Chilean Andes (and smaller correlative faunas from Argentine Patagonia) that lies near the Eocene–Oligocene transition. Tinguirirican faunas occur within a previously poorly sampled temporal interval, a significant gap in the SALMA succession, accounting for the very high percentage of taxa that are new. The Tinguirirican includes a suite of taxa not documented to co-occur elsewhere. It is defined by the first stratigraphic occurrences of taxa known elsewhere only from younger beds: caviomorph rodents; interatheriine interatheriids; an otherwise Deseadan and younger clade of notohippids, diagnosed by hypsodont lower incisors; the clade of archaeohyracids including those taxa more closely related to Archaeohyrax than to Pseudhyrax; leontiniids; and the clade of groeberiid marsupials stemming from the most recent common ancestor of Klohnia and Patagonia. Among its numerous noteworthy occurrences, the Tinguiririca Fauna includes the earliest rodents known from South America (documenting that caviomorphs had reached the continent near or before the Eocene/Oligocene boundary, with an African origin for the clade – based on preliminary phylogenetic analysis), an unusual diversity of therian species possessing a ‘gnawing’ dentition, and the world’s oldest mammalian herbivore assemblage dominated by species with hypsodont cheek teeth. The Tinguirirican assemblages indicate that Simpson’s ‘Second Faunal Stratum’ began considerably earlier (prior to the Deseadan) than previously thought. The stratotype sequence for the Tinguirirican SALMA assemblage in Chile has yielded high-precision 40Ar/39Ar radioisotopic dates, as have underlying non-fossiliferous beds. These indicate that the fauna is at least ∼31.5 Ma in age. While it potentially spans a range as large as 31–37.5 Ma or more, various lines of evidence hint that this SALMA is probably of short duration (possibly less than 2 m.y.). Body size distributions (cenograms), dental hypsodonty levels, and macroniche categories are employed to infer paleoenvironmental conditions for the Tinguiririca Fauna. Collectively, these analyses reveal some non-analog aspects of middle Cenozoic South American localities relative to modern systems; that an open, relatively dry habitat (with a mean annual rainfall of 1100 mm or less) was present at Tinguiririca, and that the most dramatic shift in Cenozoic South American paleoecology and paleoenvironment occurred between the Mustersan and Tinguirirican SALMAs. Additionally, the Tinguiririca Fauna is the first Cenozoic mammal assemblage dominated by hypsodont taxa (at levels dramatically higher than those of preceding times). The proportion of hypsodont taxa in modern assemblages correlates positively with the amount of open habitat, indicating that open habitat grassland/woodland environments flourished 15–20 million years earlier in South America than on other continents. Indeed, the Tinguiririca Fauna exhibits a proportion of hypsodont taxa exceeding even that seen in modern open habitats. Such faunas and habitats thus occur in very close proximity to the Eocene/Oligocene boundary and earliest Oligocene climatic ‘deterioration’, and their associated paleoclimatic and paleoenvironmental events. The mid-latitude Tinguiririca Fauna suggests complex biogeographic patterns during the early–middle Cenozoic – while it is decidedly ‘Patagonian’ in taxonomic composition, several members of the fauna hint at close affinities with lower latitude assemblages.

THE FIRST CENOZOIC MAMMAL FAUNA FROM THE CHILEAN ALTIPLANO

Despite its richness, South Americas Cenozoic mammal record is strongly biased geographically towards a small portion of the continent, mainly Patagonia. The rapidly growing list of major Cenozoic localities at lower latitudes thus marks a significant advance in our understanding of mammalian evolution in South America (see summaries in Flynn and Swisher, 1995; Flynn and Wyss, 1998). This paper reports the discovery of the first Cenozoic mammal fauna known from the Chilean Altiplano. It is part of an ongoing collaborative effort to sample faunas of a variety of ages across a large latitudinal transect of western South America, the goal of which is to elucidate temporal patterns of provincialism within the continent, as well as the tectonic and uplift history of the Andes Mountains and associated paleoenvi

Tele-Immersion: Preferred Infrastructure for Anatomy Instruction.

UNDERSTANDING SPATIAL RELATIONSHIPS among anatomic structures is an essential skill for physicians. Traditional medical education—using books, lectures, physical models, and cadavers—may be insufficient for teaching complex anatomical relationships. This study was designed to measure whether teaching complex anatomy to medical students using immersive virtual reality is an improvement over traditional methods. Using a networked immersive virtual reality system, anatomy-teaching assistants gave 20-minute workshops to first-year medical students one day before or after a traditional three-hour lecture/laboratory session. Students who attended only the traditional session served as a comparison group. Improvements from pretest to posttests demonstrated a statistically significant advantage to the brief virtual reality session over the traditional session. Improvement for those who were exposed to both the traditional and immersive sessions was also statistically better than for those exposed only to the traditional session. The application tested proved to be an effective enhancement to traditional surgical-anatomic educational curricula.