The Anatomy of the World's Largest Extinct Rodent

Universität Tübingen, Spezielle Zoologie, Auf der Morgenstelle 28, D-72076 Tübingen, Germany.
Science (Impact Factor: 33.61). 10/2003; 301(5640):1708-10. DOI: 10.1126/science.1089332
Source: PubMed


Phoberomys is reported to be the largest rodent that ever existed, although it has been known only from isolated teeth and fragmentary
postcranial bones. An exceptionally complete skeleton of Phoberomys pattersoni was discovered in a rich locality of fossil vertebrates in the Upper Miocene of Venezuela. Reliable body mass estimates yield
∼700 kilograms, more than 10 times the mass of the largest living rodent, the capybara. With Phoberomys, Rodentia becomes one of the mammalian orders with the largest size range, second only to diprotodontian marsupials. Several
postcranial features support an evolutionary relationship of Phoberomys with pakaranas from the South American rodent radiation. The associated fossil fauna is diverse and suggests that Phoberomys lived in marginal lagoons and wetlands.

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    • "Diprotodontia is anatomically and ecologically highly diverse, and includes wombats (Vombatidae), koalas (Phascolarctidae), three families of kangaroos and wallabies (Hypsiprymnodontidae, Macropodidae and Potoroidae), and six families of possums (Acrobatidae, Burramyidae, Petauridae, Pseudocheiridae, Phalangeridae and Tarsipedidae). Their unusual diversity also harbours the greatest size range of all mammalian orders (Sánchez-Villagra et al. 2003): the smallest diprotodontian, Tarsipes rostratus, weighs only 7 g, while the largest known species, Diprotodon optatum (which became extinct within the last 50 thousand years), would probably have weighed nearly 3 tons (Wroe et al. 2004). "
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    ABSTRACT: This chapter provides an evolutionary context to comparative research on monotremes and marsupials. It explains the evolutionary origins of the three mammalian clades in the mammalian (and pre-mammalian) from the ancient lineage of synapsids, summarizes their most obvious biological differences, and briefly the difference between the terms “Monotremata, Marsupialia, Placentalia” vs. “Prototheria, Metatheria, Eutheria”. The monotreme and marsupial families are briefly introduced through short characterizations of their general biology and evolution. An up-to-date family-level phylogeny is provided for marsupials, together with a summary of previous, morphology-based phylogenetic hypotheses vs. more recent molecular works. The fossil record for both radiations is summarized in a biogeographical context. Particular attention is given to a recent paradigm shift on monotreme evolution, with the latest research suggesting that monotremes are part of an ancient, Gondwanan radiation of mammals with independently derived tribosphenic dentition. The unusual biogeography of marsupials and their extinct relatives, including a possible origin near China and final distribution across South America, Antarctica, and Australia, is also covered.
    Full-text · Chapter · Nov 2015
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    • "If this is correct, it seems reasonable to assume that the origin of Brazil nut as a species may also be placed in this time period. Rodent diversity during the Neogene up to the early Pleistocene was much higher than today, and included large species with body masses of up to a tonne, and incisor teeth of over 30 cm (S anchez-Villagra et al., 2003; Rinderknecht & Blanco, 2008). Co-evolution with massive rodents seems a more plausible explanation for Brazil nut's investment in an energy-expensive double protection layer for its seeds than with the current scatterhoarding rodents. "
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    ABSTRACT: Aim Our goal was to test the hypothesis that ancient humans substantially contributed to shaping the current distribution of Brazil nut (Bertholletia excelsa), an Amazonian tree species that has been important for human livelihoods since pre-Columbian times. We scrutinized the putative association between Brazil nut and Amazonian Dark Earth soils (ADE) and geometric earthworks called geoglyphs, and examined the existence of continental patterns in human footprints on Brazil nut stands. Location Amazon Basin. Methods We carried out a spatially explicit meta-analysis of the variation of Brazil nut stand metrics across the Amazon Basin based on 87,617 density estimates, and 488 average stand diameter assessments, and related these to previously published datasets and suitability maps of Brazil nut, ADE and geoglyphs. Results We found consistently higher Brazil nut suitability scores, stand densities and average stand diameters in the vicinities of ADE than at larger distances, regardless of their position along a gradient from south-western to north-eastern Amazonia. For geoglyph sites such a pattern was only found for Brazil nut habitat suitability scores. The available data further revealed an accumulation of Brazil nut stands with increasing densities and average diameters from south-western to central and eastern Amazonia. Main conclusions Our findings suggest that the chance of encountering Brazil nut stands bearing the marks of past human influences increases from south-western to central and eastern Amazonia. In south-western Amazonia, the regeneration of Brazil nut seems to have been controlled predominantly by natural processes, whereas in central and eastern Amazonia, anthropogenic disturbance has been more important since pre-Columbian times. However, it remains challenging to disentangle human influences on the distribution and abundance of Brazil nut from existing environmental gradients across the Amazon Basin. In general, the results of this meta-analysis bode well for the future coexistence of Brazil nut with different forms of contemporary human land use. Keywords: Amazonian Dark Earth soils, Brazil nut, disturbance, genetic diversity, geoglyphs, historical ecology, megafauna, palaeodistribution, seed dispersal anachronism, terra preta.
    Full-text · Article · May 2015 · Journal of Biogeography
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    • "South American rodents belong to Caviomorpha [21] and evolved during the last 45 million years from hystricognath forms that invaded South America (most likely from Africa) during the Paleogene [13], [20], [22]–[29]. Caviomorphs underwent an extraordinary evolutionary radiation that made this group the rodent clade with the greatest morphological and ecological disparity, including the broadest range of body size within Rodentia [30]–[34]. Examples of the diversity of caviomorph rodents are porcupines (Erethizontoidea), coypus, degus, and spiny rats (Octodontoidea), viscachas, chinchillas, and pacaranas (Chinchilloidea), and capybaras, maras, cavies (or ‘guinea pigs’), and pacas (Cavioidea) [34], [35]. "
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    ABSTRACT: Background Caviidae is a diverse group of caviomorph rodents that is broadly distributed in South America and is divided into three highly divergent extant lineages: Caviinae (cavies), Dolichotinae (maras), and Hydrochoerinae (capybaras). The fossil record of Caviidae is only abundant and diverse since the late Miocene. Caviids belongs to Cavioidea sensu stricto (Cavioidea s.s.) that also includes a diverse assemblage of extinct taxa recorded from the late Oligocene to the middle Miocene of South America (“eocardiids”). Results A phylogenetic analysis combining morphological and molecular data is presented here, evaluating the time of diversification of selected nodes based on the calibration of phylogenetic trees with fossil taxa and the use of relaxed molecular clocks. This analysis reveals three major phases of diversification in the evolutionary history of Cavioidea s.s. The first two phases involve two successive radiations of extinct lineages that occurred during the late Oligocene and the early Miocene. The third phase consists of the diversification of Caviidae. The initial split of caviids is dated as middle Miocene by the fossil record. This date falls within the 95% higher probability distribution estimated by the relaxed Bayesian molecular clock, although the mean age estimate ages are 3.5 to 7 Myr older. The initial split of caviids is followed by an obscure period of poor fossil record (refered here as the Mayoan gap) and then by the appearance of highly differentiated modern lineages of caviids, which evidentially occurred at the late Miocene as indicated by both the fossil record and molecular clock estimates. Conclusions The integrated approach used here allowed us identifying the agreements and discrepancies of the fossil record and molecular clock estimates on the timing of the major events in cavioid evolution, revealing evolutionary patterns that would not have been possible to gather using only molecular or paleontological data alone.
    Full-text · Article · Oct 2012 · PLoS ONE
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