THE TRIASSIC FLORA FROM THE EL TRANQUILO GROUP, PROVINCE OF SANTA CRUZ (PATAGONIA): FOSSIL WOODS. Anatomical studies of gymnosperms from the Laguna Colorada Formation of El Tranquilo Group (Upper Triassic) from Santa Cruz Province, Argentina, are presented. The following taxa are described: Araucariaceae: Agathoxylon lamaibandianus sp. nov., Agathoxylon dallonii (Boureau) Crisafulli and Herbst comb. nov., Agathoxylon amraparense (Sah and Jain) Crisafulli and Herbst comb, nov.; Podocarpaceae: Podocarpoxylon indicum (Bardwaj) Bose and Maheshwari, Podocarpoxylon paralatifolium Vozenin-Serra and Grant-Mackie, Protophyllocladoxylon sp., and a new species of the ginkgoalean, Ginkgophytoxylon isychozianus Crisafulli and Herbst sp. nov., which is well diferentiated from the other two Permian species of the genus recorded from France, New Mexico (USA) and Uruguay. The validity of the latter genus is discussed and mantained. Some comments are made on the paleoclimatic conditions indicated by the characters of cells of secondary xylem in their growth rings.

PALEOECOLOGY OF FORAMINIFERA FROM A HOLOCENE CORE RECOVERED IN THE COASTAL PLAIN OF MAR CHIQUITA LAGOON, BUENOS AIRES, ARGENTINA. Foraminifera associations from a 182 cm long sediment core drilled east of Mar Chiquita Lagoon were studied in order to provide evidence of Holocene paleoenvironmental evolution and its probable relationship with the last transgressive-regressive cycle. A total of 91 taxa were recorded. The most frequent and abundant species were Buccella peruviana (d'Orbigny) f. campsi (Boltovskoy) and Elphidium discoidale (Boltovskoy) followed by Ammonia beccarii s.l. (Linné) and Elphidium gunteri Cole. Qualitative and quantitative analyses allowed the recognition of four sections and three main stages in the paleoenvironmental evolution of the studied sequence. In the first stage (Section A) previous to 8500 years BP, estuarine and low salinity conditions would have prevailed; it should be associated to a low sea-level position before sea advance over the continent. In a second stage (Sections B-C) deposited between ca. 8000 and 5000 years BP, marine influence increased probably representing the transgressive event; the early stages of a gradual decrease of marine influence is noted towards the top of Section C. Finally, the third stage (Section D) —after 5000 years BP— reveals a progressive evolution towards brackish, low energy and more restricted environments. This last phase may be explained by the onset of the sand-dune barrier during the regressive phase of the Holocene transgression as proposed by other authors.

The goal of this study is to evaluate ecomorphological variables in glyptodonts from different ages (Miocene to early Holocene), clades, and sizes, with the purpose of inferring their habitats and feeding habits. The analyses included estimation of body masses and three variables: relative muzzle width (RMW), hypsodonty index (HI), and dental occlusal surface area (OSA). RMW allows the distinction of two main groups: the small-sized early Miocene propalaehoplophorids were selective feeders, while the larger post-Miocene forms were more bulk feeders. The Pleistocene Glyptodon appears as an exception, implying a reversion to a selective feeding behavior. The relation between RMW and HI allows discriminating feeding niche partitioning in glyptodonts. Among the early Miocene propalaehoplophorids, Eucinepeltus would have been a highly selective feeder in relatively closed environments, Propalaehoplophorus a highly selective feeder in moderately open habitats, and Cochlops a less selective feeder in moderately open habitats. Among the large Pliocene and Pleistocene taxa, cf. Neuryurus and Neosclerocalyptus were probably bulk feeders in relatively open environments, while Panochthus and Doedicurus were bulk feeders in open environments. Alternative interpretations can be assessed for Glyptodon: it was a more selective feeder in closer habitats, or had a different feeding behavior, browsing on specific plants at higher levels from the ground, and/or a specialized physiology. The late Miocene and Pliocene forms (Hoplophractus, Eosclerocalyptus, and Urotherium) were probably intermediate between the Miocene and the Pleistocene ones.

PALAEOFLORISTIC ANALYSIS OF THE RIO GUILLERMO FORMATION (LATE EOCENE-EARLY OLIGOCENE?), SANTA CRUZ, ARGENTINA. Macrofloristic Paleogene units of southernmost Patagonia have few palaeobotanical studies. In this paper a new fossil leaf collection recovered from the Río Guillermo Formation (late Eocene—early Oligocene?) is analyzed. The palaeobotanical analysis reveals the presence of 10 fossil species, most of them related to Nothofagus Blume (Nothofagaceae), being the specimens of “Myrcia” bagualensis (Myrtaceae) the most abundant in the collection. Specimens referred to the families Rosaceae, Anacardiaceae, Lauraceae and Fagaceae were also recognized. The palaeofloristic assemblage from the Río Guillermo Formation is dominated by cold temperate taxa suggesting the presence of subantarctic paleofloras in this area. The great similarities between the Río Guillermo flora and that of the Oligocene Loreto Formation, coupled with the palaeoclimatic inferences, might indicate a younger age than previously suggested for the Río Guillermo Formation.

RODENTS AND MARSUPIALS AT THE PLEISTOCENE—HOLOCENE BOUNDARY IN CATAMARCA, ARGENTINA: EXTINCTIONS AND ENVIRONMENTAL EVOLUTION. A fossil small-mammal assemblage from the neighborhood Las Juntas, Catamarca, Argentina (28°06′36″S–65°53′54″W, 1562 m) was studied. A radiocarbon dating on a sample of long bones referred them to late Pleistocene (13.4–13.0 cal ky). The assemblage includes twelve species, dominated by the sigmodontine rodents Reithrodon auritus (Fischer) and Phyllotis sp., followed by Akodon spegazzinii Thomas and Andinomys edax Thomas. The presence of the caviomorph Abrocoma cinerea Thomas, and the sigmodontines Akodon simulator Thoma s and Tafimys powelli Ortiz, Pardiñas and Steppan is remarkable. A Didelphimorphia, Thylamys sp., is also present. The surface of the bones and teeth shows microscopical evidences of corrosion, indicating that the sample was generated by the predatory activity of owls. The identified species correspond to elements of high-altitude open environments, a mixture of cloud highland-grasslands, high-Andean grasslands, and scarce elements of upper montane forest. Most of them are currently sympatric at an altitude of approximately 2500 m in the same mountain range, in a colder and drier environment than that recorded at the studied site. It is suggested that paleoenvironmental conditions during deposition of the assemblage were colder and drier. It is not possible to extrapolate these data to other areas because of the great orographic and environmental variation in the region, which determines different small-mammal assemblages across relatively reduced geographic areas.

WEAR PATTERN AND OCCLUSION IN THE MASTICATORY SYSTEM OF EXTINCT ARGYROLAGOIDEA (MARSUPIALIA, POLYDOLOPIMORPHIA, BONAPARTHERIIFORMES). The Argyrolagoidea (Mammalia, Marsupialia, Polydolopimorphia, Bonapartheriiformes) display a pattern of cusp contact that is quite different from any other group of South American metatherians during dental occlusion. The resulting pattern of wear facets is also exclusive for this group. In part, this is due to the highly derived molar morphology of argyrolagoids as compared to the generalized tribosphenic pattern. The location and relative development of wear facets indicate that chewing movements were composed of propalinal and ectental components, resulting in an oblique motion. This type of masticatory dynamics correlates with the argyrolagoid molar pattern, including a reorganization of cusps and the addition of neomorphic structures. This pattern of molar wear, the occlusal movements, and the acquisition of hypsodonty strongly support the hypothesis of an herbivorous diet for this group. The occurrence of hypsodonty in South American metatherians already by the early Oligocene appears to be a remarkably rapid response to environmental changes. Body mass estimates are consistent with those of many small herbivores (i.e., rodents).

ECOMORPHOLOGY OF EXTINCT XENARTHRANS: ANALYSIS OF THE MANDIBLE USING GEOMETRIC MORPHOMETRICS METHODS. In the past, xenarthrans had a broad morphological diversity. However, due to the fact that extant species are dissimilar to most of the extinct ones, few ecomorphological studies have been carried out on this group. The aim of this work is to infer the diet of some extinct xenarthrans species by means of taxon free shape patterns related to diet, working with a taxonomically wide comparative sample. A geometric morphometrics analysis was developed on the lateral view of mandibles of xenarthrans, ungulates and species of other orders. Combining the results of principal component and canonical variate analyses, it was possible to characterize the shape of insectivorous species, which show a high degree of homoplasy. Omnivorous species share some morphological characteristics with herbivorous species with functional canines or high quantities of fruit in their diet. Armadillos show an extremely reduced coronoid process whereas ruminants have a much developed angular process. It was not possible to infer diet in gliptodonts, which behave as outliers in all analyses. The results obtained for most of the ground sloths and Vassallia maxima agree with those of previous studies on these species, thus supporting an ecomorphological approach on extinct Folivora. However, the PCA results suggest an omnivorous/frugivorous diet for Scelidotherium sp. and Thalassocnus natans, although they have been traditionally described as herbivorous. New analyses including the skull are needed to confirm this diet in both cases.