Monotremata is a clade of egg-lying mammals, represented by the living platypus and echidnas, which is endemic to Australia, and adjacent islands. Occurrence of basal monotremes in the Early ...Cretaceous of Australia has led to the consensus that this clade originated on that continent, arriving later to South America. Here we report on the discovery of a Late Cretaceous monotreme from southern Argentina, demonstrating that monotremes were present in circumpolar regions by the end of the Mesozoic, and that their distinctive anatomical features were probably present in these ancient forms as well.
The fossil record of abelisaurid theropods in South America is mostly limited to Brazil and Argentina. In Argentina, abelisaurids are generally known from Patagonia, where their record is relatively ...abundant and includes well-known and complete specimens. However, for North-western Argentina, abelisaurids are represented by incomplete and isolated bones and teeth that remain largely unpublished. The aim of this contribution is to report a nearly complete abelisaurid braincase from the Late Cretaceous Los Blanquitos Formation (Campanian), Amblayo Valley, Salta province, Argentina. The specimen shows plesiomorphic features for abelisaurids, including a thin skull roof, absence of skull projections like horns or bulges, and low and narrow parietal eminence that lie at the same level as the sagittal crest. Furthermore, the specimen possesses some autapomorphies that support its status as a new taxon and its small size allows it to be assigned as one of the smallest abelisaurids recorded up to date. The finding of this specimen constitutes the first unequivocal occurrence of an abelisaurid in Northwestern Argentina and brings new evidence concerning the geographic distribution of the clade during Late Cretaceous times in South America.
The Chañares Formation (latest Middle–earliest Late Triassic) of northwestern Argentina is part of the Ischigualasto–Villa Unión Basin and preserves a rich fossil vertebrate record discovered by a ...crew of the Museum of Comparative Zoology (Harvard University) led by Alfred Romer. A diverse non-dinosaurian dinosauromorph assemblage has been described from this formation and includes the iconic, small-sized “proto-dinosaur” Lagosuchus talampayensis Romer, 1971. This species has been crucial to understand the body plan of dinosaur precursors and the higher-level phylogenetic relationships of dinosaurs. More recently, authors considered this genus and species as nomina dubia. The aim of this contribution is to reassess the taxonomic validity of L. talampayensis. New observations indicate that the holotype of L. talampayensis differs from other avemetatarsalians, but not from the hypodigm of Marasuchus lilloensis, in the presence of a globose femoral head (strongly convex proximal and medial surfaces) with a distinctly dorsal orientation and a sub-oval outline in proximal view as a result of incipient posterior and posteromedial tuberosities. Thus, Lagosuchus talampayensis is here considered a senior synonym of “Marasuchus lilloensis” (Romer, 1972). Our conclusions have implications in the knowledge about early dinosauromorph diversity and the taxonomic richness of the group in the Chañares Formation.
Lewisuchus admixtus is a basal dinosauriform coming from Late Triassic outcrops of NW Argentina. Although this taxon was recently anatomically restudied, histological data is still wanting. The ...microstructure of the long bones (femur and two tibie) reveals a relatively fast rate of growth, comparable with that seen in other basal Dinosauriformes and basal dinosaurs. Cortical bone is comprised of fibro-lamellar complex in one femur and tibia, but parallel-fibered matrix are observed in the other tibia. The secondary remodelling of bone is poor and there is not growth marks. The vascularization is relatively dense, longitudinal, laminar and reticular. There are some features that indicate slowdown of the growth at late age of the specimens. The fast growth of L. admixtus implies a relatively high metabolic rate. This is probably related with environmental conditions.
The fossil record of post-Paleozoic lungfishes in Greenland is currently restricted to a few brief reports of isolated and undetermined tooth plates coming from the uppermost Fleming Fjord Formation ...(late Norian) in Jameson Land, central East Greenland. Here, we describe Ceratodus tunuensis, sp. nov., a new dipnoan from a thin bed of calcareous lake mudstone from the Ørsted Dal Member of the Fleming Fjord Formation. The Ceratodus fossil record indicates that during the Late Triassic, this genus was restricted to the middle latitudes of the Northern Hemisphere. This record matches previous paleobiogeographical analyses and indicates that terrestrial biota during the Late Triassic was strongly influenced by paleolatitude.
The first fossil remains of vertebrates, invertebrates, plants and palynomorphs of the Chorrillo Formation (Austral Basin), about 30km to the SW of the town of El Calafate (Province of Santa Cruz), ...are described. Fossils include the elasmarian (basal Iguanodontia) Isasicursor santacrucensis gen. et sp. nov., the large titanosaur Nullotitan glaciaris gen. et sp. nov., both large and small Megaraptoridae indet., and fragments of sauropod and theropod eggshells. The list of vertebrates is also composed by the Neognathae Kookne yeutensis gen. et sp. nov., two isolated caudal vertebrae of Mammalia indet., and isolated teeth of a large mosasaur. Remains of fishes, anurans, turtles, and snakes are represented by fragmentary material of low taxonomical value, with the exception of remains belonging to Calyptocephalellidae. On the other hand, a remarkable diversity of terrestrial and freshwater gastropods has been documented, as well as fossil woods and palinological assemblages. The Chorrillo Formation continues south, in the Las Chinas River valley, southern Chile, where it is called Dorotea Formation. Both units share in their lower two thirds abundant materials of titanosaurs, whose remains cease to appear in the upper third, registering only elasmarians (Chorrillo Formation) and hadrosaurs (Dorotea Formation). Above both units there are levels with remains of invertebrates and marine reptiles. It is striking that the dinosaurs of the lower two thirds of the Chorrillo and Dorotea formations are represented by large basal titanosaurs and Megaraptoridae coelurosaurs, being the Saltasaurinae and Aeolosaurinae sauropods and Abelisauridae theropods totally absent. In contrast, these taxa are dominant components in sedimentary units of central and northern Patagonia (e.g., Allen, Los Alamitos, La Colonia formations). Such differences could reflect, in part, a greater antiquity (i.e., late Campanian-early Maastrichtian) for the Chorrillo fossils, or, more probably, different environmental conditions. Thus, knowledge of the biota of the southern tip of Patagonia is expanded, particularly those temporarily close to the K-Pg boundary.
Here we describe isolated avian remains coming from the Chichinales Formation, at the Paso Córdoba locality, Río Negro province, Patagonia, Argentina. Present report constitutes the first analysis of ...an Early Miocene bird association in South America outside the Santa Cruz and Chubut provinces, and one of the scarce reports of avian remains for the Colhuehuapian SALMA. The remains represent a new genus and species of phorusrhacid (Patagorhacos terrificus gen. et sp. nov.), a new species of rheid (Opisthodactylus horacioperezi sp. nov.), and an indeterminate charadriiform. Although different in composition, the presence and relative abundance of rheids and phorusrhacids is a pattern that is also present in other Early Miocene Patagonian assemblages, especially those from the Santacrucian SALMA. In spite of such similarities, the description of new taxa indicates that the Chichinales faunas were different to some degree from other Early Miocene bird assemblages.
Des restes fossiles isolés d’oiseaux provenant de la localité argentine de Paso Córdoba (Formation Chichinales, Province du Río Negro, Patagonie) sont décrits. Cette étude constitue la première analyse d’un assemblage avien du Miocène inférieur d’Amérique du Sud (en dehors des provinces de Santa Cruz et de Chubut), et l’un des rares signalements d’oiseaux fossiles pour le Colhuehuapien SALMA. Les restes décrits représentent un nouveau genre et une nouvelle espèce de phorusrhacidé (Opisthodactylus horacioperezi sp. nov.), une nouvelle espèce de rhéidé (Opisthodactylus horacioperezi sp. nov.), et un charadriiforme indéterminé. Bien que différent dans sa composition, cet assemblage montre une proportion de rhéidés et phorusrhacidés similaire à ce qui est observé dans les assemblages du Miocène inférieur de Patagonie, notamment ceux du Santacrucien SALMA. Malgré ces similitudes, la description de nouveaux taxons indique que les avifaunes de la Formation Chichinales étaient quelque peu distinctes de celles des autres formations du Miocène inférieur.
Since its original description as a feather belonging to a basal bird, the phylogenetic position of Praeornis sharovi was debated. It was considered as belonging to a bird, a cycad leaf, or as a ...'transitional' integumentary structure between reptile scales and bird feathers. Recently, a basal enantiornithine bird was collected in Early Cretaceous beds of Brazil. This specimen shows very well-preserved rachis-dominated tail feathers with a very thick rachis and thick and rigid barbules. These features are present in Praeornis, suggesting that this fossil may be interpreted as the tail feather of a basal bird. In this way, Praeornis constitutes one of the oldest records of rachis-dominated feathers in the world. Rachis-dominated tail feathers, including that of Praeornis appear to be rigid paired structures not performed for aerodynamical purposes, suggesting that may be important in body balance.
Marsh rats of the species
inhabit mesic and humid environments. For this reason, it is frequently used in paleoenviromental studies to infer past humid conditions. Holocene archeological record ...indicates that
had a wider geographical distribution than today. Its regional extinction in north Patagonia at the XIX century was attributed to the dry and cold Little Ice Age (LIA). Here we present the finding of a specimen of
from northeastern Patagonia (Valcheta stream, Río Negro province, Argentina), just at the end of LIA. Implications of this novel historical record are discussed.
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