Rosendo Pascual

Main Pathways of Mammalian Diversification in South America

The most complete record of the continental mammal-bearing Cenozoic of South America comes from Argentina (Marshall et al., 1983a, 1984). This record, representing the southernmost part of the continent, became a unique example in which to study the evolutionary events affecting its mammal communities in relation to the outstanding climatic and environmental changes (Pascual, 1984). The main patterns of geological evolution in this southern part of the continent had a profound influence on its mammalian history. The chronostratigraphic diagrams (Figs. 1 and 2) show the geographical and chronological distribution of Cenozoic sedimentary and volcanic rocks in eastern and western Argentina. This lithostratigraphic distributional pattern makes evident the following historical facts:

The first gnathic remains of Sudamerica: implications for gondwanathere relationships

ABSTRACT The Gondwanatheria is an enigmatic group of mammals known from the Late Cretaceous and Paleocene of Argentina and the Late Cretaceous of Madagascar and India. Although originally believed to be edentates, it has been argued recently that gondwanatheres comprise a derived clade of multituberculates. Aside from two tentatively referred, fragmentary dentaries (one edentulous and the other bearing a single tooth), each of the four named species of gondwanatheres is based only on isolated teeth. The discovery of a nearly complete dentary of the sudamericid gondwanathere Sudamerica ameghinoi provides important new anatomical information concerning the morphology of the lower jaw, the association and orientation of lower cheek-teeth, the direction of jaw movement, and the lower dental formula and thereby necessitates another reevaluation of the relationships of Gondwanatheria. Analysis of this specimen, which contains two molariform cheek-teeth and alveoli for two more, casts doubt on the hypothesis tha...

First gondwanatherian mammal from Antarctica

Abstract Gondwanatherians are an enigmatic group of extinct non-therian mammals apparently restricted to some of the western Gondwanan continents (Late Cretaceous-early Palaeocene of South America, and Late Cretaceous of Madagascar and India). They developed rodent-like incisors and the earliest known hypsodont cheek-teeth among mammals. Recently, a small rodent-like dentary fragment was recovered from middle Eocene beds on the Antarctic Peninsula, preserving part of the incisor; both the incisor enamel structure and the mandibular morphology suggest close affinities with Sudamerica ameghinoi from the early Palaeocene of Patagonia, up to now the youngest known Gondwanatheria. Thus, the new specimen becomes the youngest occurrence of a gondwanathere, adding significant direct and indirect evidence on: (1) the already documented cosmopolitanism of gondwanatheres among Gondwanan mammals; and (2) the crucial biogeographical role of Antarctica during the Cretaceous-Tertiary mammalian transition.

The Schmelzmuster of the Paleogene South American rodentlike marsupialsGroeberia andPatagonia compared to rodents and other Marsupialia

KurzfassungDer Schmelz der unteren Schneidezähne vonGroeberia andPatagonia, zweier nagetierartiger Beutler aus Südamerika, wurde untersucht. Das Schmelzmuster ist in beiden Gattungen durch das Fehlen von Hunter-Schreger-Bändern grundsätzlich von Nagetieren unterschieden, ungeachtet der morphologischen ähnlichkeiten der Bezähmungen. Ein ähnliches Schmelzmuster wird zwar für das Kän-guruhMacropus rufus beschrieben, aber diese übereinstimmung allein wäre ein schwaches Argument, die beiden Gattungenzu den Maisupialia zu stellen, weil Konvergenzen bei der Evolution des Zahnschmelzes häufig vorkommen. ähnlichkeiten in den funktionellen Anforderungen, wie eine Bruchsicherung, mögen zu dieser übereinstimmung geführt haben. Damit beweist das Schmelzmuster der Groeberiidae und Patagoniidae den Unterschied gegenüber allen Rodentia. Die Zugehörigkeit zu den Marsupialia belegen Merkmale von Schädel und Kiefer.AbstractThe enamel of the lower incisors of two Paleogene South American rodent-like marsupialsGroeberia minoprioi (Groeberiidae) andPatagonia peregrina (Patagoniidae) is described. The fact that the Schmelzmuster lacks Hunter-Schreger bands proves that these genera are basically different from any rodent despite other morphological similarities. Although the enamel is like that of the kangaroo,Macropus rufus, it is not sufficient evidence to include these genera in the Marsupialia. Convergence, based on functional requirements, such as crack stopping mechanisms, is common in the evolution of enamel. Therefore, the Schmelzmuster testifies to the distinctness of the Groeberiidae and Patagoniidae from any rodent; their marsupial nature is based on craniomandibular characters.