Sparassodonta

Abstract: Preface 1. Introduction 2. Phylogenetics of characters and groups, and the classification of taxa 3. Problems in understanding metatherian evolution 4. Form-function, and ecological and behavioural morphology in Metatheria 5. Background to the analysis of metatherian cruropedal evidence 6. Mesozoic and Cenozoic: fossil tarsals of ameridelphians unassociated with teeth 7. Cruropedal attributes of living and fossil families of metatherians 8. Taxa and phylogeny of Metatheria 9. Paleobiogeography and metatherian evolution References Index.

Abstract: Recent studies show Xenarthra to be even more isolated systematically from other placental mammals than traditionally thought. The group not only represents 1 of 4 primary placental clades, but proposed links to other fossorial mammal taxa (e.g., Pholidota, Palaeanodonta) have been contradicted. No unambiguous Paleocene fossil xenarthran remains are known, and Eocene remains consist almost exclusively of isolated cingulate osteoderms and isolated postcrania of uncertain systematic provenance. Cingulate skulls are unknown until the late middle Eocene, and the oldest sloth and anteater skulls are early Oligocene and early Miocene age, respectively; there are no nearly complete xenarthran skeletons until the early Miocene. Ecological reconstructions of early xenarthrans based on extant species and the paleobiology of extinct Neogene taxa suggest the group's progenitors were myrmecophagous with digging and perhaps some climbing adaptations. The earliest cingulates were terrestrial diggers and likely myrmecoph...

Abstract: South America was isolated from other continents during most of the Cenozoic, developing a singular mammalian fauna. In contrast to North America, Europe, Asia, and Africa, up to the late Neogene, the carnivore adaptive zone in South America was populated by crocodiles (Sebecidae), large snakes (Madtsoiidae), large birds (Phorusrhacidae), and metatherian mammals (Sparassodonta). Sparassodonta were varied and comprised a wide range of body masses (≈ 2–50 kg) and food habits. Their diversity decreased towards the late Miocene (Huayquerian Stage/Age) and the group became extinct in the “middle” Pliocene (≈ 3 Ma, Chapadmalalan Stage/Age). Several authors have suggested that the cause of this decline and extinction was the ingression of carnivorans to South America (about 6–7 Ma ago), because they competed with the Sparassodonta; although this hypothesis has been criticized in recent years. With the intention of testing the hypothesis of “competitive displacement,” we review the fossil record of South American Sparassodonta and Carnivora, collect data about diversity, estimate size and diet, and determine first and last appearances. The diversity of Sparassodonta is low relative to that of Carnivora throughout the Cenozoic with the early Miocene (Santacrucian Stage/Age) showing the greatest diversity with 11 species. In the late Miocene-middle Pliocene (Huayquerian Stage/Age), the fossil record shows overlap of groups, and the Sparassodonta’s richness curve begins to decline with the first record of Carnivora. Despite this overlap, carnivorans diversity ranged from four or fewer species in the late Miocene-Pliocene to a peak of around 20 species in the early Pleistocene (Ensenadan Stage/Age). Carnivora was initially represented by small-sized, omnivorous species, with large omnivores first appearing in the Chapadmalalan Stage/Age. Over this period, Sparassodonta was represented by large and small hypercarnivores and a single large omnivorous species. From this review of the fossil record, it is suggested that factors other than competitive displacement may have caused the extinction of the Sparassodonta.

Abstract: Fil: Prevosti, Francisco Juan. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; Argentina