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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    • "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.
    Journal of Biogeography 05/2015; 42:1367–1382. · 4.59 Impact Factor
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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.
    PLoS ONE 10/2012; 7(10):e48380. DOI:10.1371/journal.pone.0048380 · 3.23 Impact Factor
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    • "The Amazonian capybara is currently the largest living rodent, but it is by no means the largest rodent ever: three now extinct larger rodent species that once roamed the Americas are the Castoroides , estimated to weigh up to 200 kg [Reynolds, 2002], Phoberomys , estimated to weigh 700 kg [Sánchez-Villagra et al., 2003], and Josephoartigasia , predicted to weigh about 1,200 kg [Rinderknecht and Blanco, 2008]. The estimated time of divergence of these species from their common ancestor with the species in the present dataset implies that the same cellular scaling rules that apply to the brains of modern Glires must also have applied to them. "
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    ABSTRACT: Brain size scales as different functions of its number of neurons across mammalian orders such as rodents, primates, and insectivores. In rodents, we have previously shown that, across a sample of 6 species, from mouse to capybara, the cerebral cortex, cerebellum and the remaining brain structures increase in size faster than they gain neurons, with an accompanying decrease in neuronal density in these structures [Herculano-Houzel et al.: Proc Natl Acad Sci USA 2006;103:12138-12143]. Important remaining questions are whether such neuronal scaling rules within an order apply equally to all pertaining species, and whether they extend to closely related taxa. Here, we examine whether 4 other species of Rodentia, as well as the closely related rabbit (Lagomorpha), conform to the scaling rules identified previously for rodents. We report the updated neuronal scaling rules obtained for the average values of each species in a way that is directly comparable to the scaling rules that apply to primates [Gabi et al.: Brain Behav Evol 2010;76:32-44], and examine whether the scaling relationships are affected when phylogenetic relatedness in the dataset is accounted for. We have found that the brains of the spiny rat, squirrel, prairie dog and rabbit conform to the neuronal scaling rules that apply to the previous sample of rodents. The conformity to the previous rules of the new set of species, which includes the rabbit, suggests that the cellular scaling rules we have identified apply to rodents in general, and probably to Glires as a whole (rodents/lagomorphs), with one notable exception: the naked mole-rat brain is apparently an outlier, with only about half of the neurons expected from its brain size in its cerebral cortex and cerebellum.
    Brain Behavior and Evolution 11/2011; 78(4):302-14. DOI:10.1159/000330825 · 2.01 Impact Factor
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