Late Pleistocene echimyid rodents (Rodentia, Hystricognathi) from northern Brazil.

Echimyidae (spiny rats, tree rats and the coypu) is the most diverse family of extant South American hystricognath rodents (caviomorphs). Today, they live in tropical forests (Amazonian, coastal and Andean forests), occasionally in more open xeric habitats in the Cerrado and Caatinga of northern South America, and open areas across the southern portion of the continent (Myocastor). The Quaternary fossil record of this family remains poorly studied. Here, we describe the fossil echimyids found in karst deposits from southern Tocantins, northern Brazil. The analyzed specimens are assigned to Thrichomys sp., Makalata cf. didelphoides and Proechimys sp. This is the first time that a fossil of Makalata is reported. The Pleistocene record of echimyids from this area is represented by fragmentary remains, which hinders their determination at specific levels. The data reported here contributes to the understanding of the ancient diversity of rodents of this region, evidenced until now in other groups, such as the artiodactyls, cingulates, carnivores, marsupials, and squamate reptiles.

A new Mammutidae (Proboscidea, Mammalia) from the Late Miocene of Gansu Province, China.

The "Yanghecun specimen", a proboscidean specimen represented by a mandible from Miocene of China and previously described as Gomphotheriidae, is here reviewed and described as a new genus and species of Mammutidae: Sinomammut tobieni. This taxon is a longirostrine mastodon, lacking lower tusks, and bearing a wide last molar with oblique and non-inflated lophids, broad transverse interlophids, and yoke-like wear figures. Phylogenetic analysis of Mammutidae based on dental and mandibular features recovered S. tobieni as sister group of the mastodon Mammut. The longirostrine condition and the well-developed lower incisors seem to be primitive for Mammutidae, while the brevirostry is the derived condition, probably emerged during the middle Miocene (12-11 Mya). However, two derived conditions are recognized to the lower tusks: the absence of lower tusks (S. tobieni) and the occasional presence of vestigial lower tusks (Mammut).

The Dance of Tusks: Rediscovery of Lower Incisors in the Pan-American Proboscidean Cuvieronius hyodon Revises Incisor Evolution in Elephantimorpha.

The incisors of proboscideans (tusks and tushes) are one of the most important feature in conservation, ecology and evolutionary history of these mammals. Although the absence of upper incisors is rare in proboscideans (occurring only in deinotheres), the independent losses of lower incisors are recognized for most of its lineages (dibelodont condition). The presence of lower incisors in the Pan-American gomphothere Cuvieronius hyodon was reported a few times in literature, but it was neglected in systematic studies. We analyzed several specimens of Cuvieronius hyodon from the Americas and recognized that immature individuals had lower incisors during very early post-natal developmental stages. Subsequently, these are lost and lower incisors alveoli close during later developmental stages, before maturity. Moreover, for the first time in a formal cladistic analysis of non-amebelodontine trilophodont gomphotheres, Rhynchotherium and Cuvieronius were recovered as sister-taxa. Among several non-ambiguous synapomorphies, the presence of lower incisors diagnoses this clade. We recognize that the presence of lower incisors in Cuvieronius and Rhynchotherium is an unique case of taxic atavism among the Elephantimorpha, since these structures are lost at the origin of the ingroup. The rediscovery of the lower incisors in Cuvieronius hyodon, their ontogenetic interpretation and the inclusion of this feature in a revised phylogenetic analysis of trilophodont gomphotheres brought a better understanding for the evolutionary history of these proboscideans.

Didelphidae marsupials (Mammalia, Didelphimorphia) from the late Pleistocene deposit of the Gruta dos Moura Cave, northern Brazil.

The present study acknowledges the diversity of fossil marsupials from the Gruta dos Moura cave, as well as environmental and climatic aspects during the Quaternary. The results show that this is the largest diversity of Pleistocene marsupials recorded in a single cave: Didelphis albiventris, D. aurita, Gracilinanus agilis, G. microtarsus, Marmosa murina, Monodelphis brevicaudata, M. domestica and Sairadelphys tocantinensis. Furthermore, the described specimens are also part of the only fossil assemblage unequivocally referable to the late Pleistocene. Paleontological studies suggest an intimate association with dry and open environments with high abundance of water sources. Since most of the identified taxa are characteristic of open forests and gallery forests, this could represent the actual environment around the Gruta dos Moura cave. Recent studies identified sympatric occurrences between species from open and dry environments and species from humid forests that were identified among our material and are characteristic of humid regions. Therefore, these species could inhabit gallery forests and capons, or even ecotones, inside a dry and open environment. Moreover, the extinction of Sairadelphys could also indicate that the climatic and environmental conditions changed or that the past environment was more heterogeneous than the current environment of the region.

Late Pleistocene carnivores (Carnivora: Mammalia) from a cave sedimentary deposit in northern Brazil.

The Brazilian Quaternary terrestrial Carnivora are represented by the following families: Canidae, Felidae, Ursidae, Procyonidae Mephitidae and Mustelidae. Their recent evolutionary history in South America is associated with the uplift of the Panamanian Isthmus, and which enabled the Great American Biotic Interchange (GABI). Here we present new fossil records of Carnivora found in a cave in Aurora do Tocantins, Tocantins, northern Brazil. A stratigraphical controlled collection in the sedimentary deposit of the studied cave revealed a fossiliferous level where the following Carnivora taxa were present: Panthera onca, Leopardus sp., Galictis cuja, Procyon cancrivorus, Nasua nasua and Arctotherium wingei. Dating by Electron Spinning Resonance indicates that this assemblage was deposited during the Last Glacial Maximum (LGM), at least, 22.000 YBP. The weasel, G. cuja, is currently reported much further south than the record presented here. This may suggest that the environment around the cave was relatively drier during the LGM, with more open vegetation, and more moderate temperatures than the current Brazilian Cerrado.

Distributional patterns of herbivore megamammals during the Late Pleistocene of South America.

The geographic distribution of 27 species of the South American megafauna of herbivore mammals during the Late Pleistocene was analyzed in order to identify their distributional patterns. The distribution of the species was studied using the panbiogeographical method of track analysis. Six generalized tracks (GTs) and two biogeographic nodes were obtained. The GTs did not completely superpose with the areas of open savanna present in Pleistocene, nor with the biotic tracks of some arthropods typical of arid climate, indicating that these animals avoided arid environment. Overall, the GTs coincided with some biogeographic provinces defined on the basis of living taxa, indicating that certain current distributional patterns already existed in Pleistocene. The biogeographic nodes coincided with the borders between the main vegetal formations of the Pleistocene, showing that the type of vegetation had great influence in the distribution of the mammalian megafauna. The node 1 confirmed the existence of contact zones between paleobiogeographic regions near Argentina-Uruguay border. The node 2 connects the Brazilian Intertropical regions.

Population structure of the gomphothere Stegomastodon waringi (Mammalia: Proboscidea: Gomphotheriidae) from the Pleistocene of Brazil.

The Quaternary fossil record of Águas de Araxá (Q AA) is represented mainly by an accumulation of skeletal elements of several sizes, which are assigned to a population of Stegomastodon waringi. We analyzed 97 molars according to the ear stages of Simpson and Paula-Couto (1957), and developed a morphometric ear index. The population structure (proportion of immature, subadult, adult, mature adult and senile adult individuals) was identified, and these five age classes were compared to those of extant elephant populations and defined with social implications. The analysis made possible to establish that the population is largely composed of adults: 14.89% are immature individuals, 23.04% subadults, 27.65% adults, 17.21% mature adults and another 17.21% senile adults. Based on population structure, we do not discard the possibility that the fossil population was stable or in recovery, and/or was experiencing a high-predation period on younger individuals. The number of individuals composing the past population studied here could suggest that the occupied environment was open due to comparisons to populations of extant elephants. We consider this population as an aggregation of family units, which suggests a time of low environmental humidity. Based on literature and our findings, their extinction appears to be regional and probably related to a catastrophic event.

Population structure of the gomphothere Stegomastodon waringi (Mammalia: Proboscidea: Gomphotheriidae) from the Pleistocene of Brazil

The Quaternary fossil record of Águas de Araxá (Q AA) is represented mainly by an accumulation of skeletal elements of several sizes, which are assigned to a population of Stegomastodon waringi. We analyzed 97 molars according to the ear stages of Sipson and Paula-Couto (1957), and developed a orphoetric ear index. The population structure (proportion of immature, subadult, adult, mature adult and senile adult individuals) was identified, and these five age classes were compared to those of extant elephant populations and defined with social implications. The analysis made possible to establish that the population is largely composed of adults: 14.89 percent are immature individuals, 23.04 percent subadults, 27.65 percent adults, 17.21 percent mature adults and another 17.21 percent senile adults. Based on population structure, we do not discard the possibility that the fossil population was stable or in recovery, and/or was experiencing a high-predation period on younger individuals. The number of individuals composing the past population studied here could suggest that the occupied environment was open due to comparisons to populations of extant elephants. We consider this population as an aggregation of family units, which suggests a time of low environmental humidity. Based on literature and our findings, their extinction appears to be regional and probably related to a catastrophic event.

O registro fossilífero do Quaternário de Águas de Araxá (QAA) é representado principalmente pelo acúmulo de restos dentários e de esqueleto de diversos tamanhos, atribuídos a uma população pretérita do mastodonte Stegomastodon waringi. Foram analisados 97 molares de acordo com os estágios de desgaste propostos por Simpson e Paula-Couto 1957, e desenvolveu-se um índice morfométrico de desgaste. A estrutura populacional (proporção entre indivíduos imaturos, subadultos, adultos, adultos maduros e adultos senis) foi identificada e comparada com populações de elefantes atuais. Foi possível estabelecer que esta população era amplamente composta por adultos: 14,89 por cento eram indivíduos imaturos; 23,04 por cento eram subadultos; 27,65 por cento eram adultos; 17,21 por cento eram adultos maduros e outros 17,21 por cento eram adultos senis. Baseados na estrutura populacional observada, não se descartou a possibilidade desta população estar estável ou em recuperação e/ou de ter passado por um período de predação dos indivíduos mais jovens. O número de indivíduos encontrados nesta população sugere que esta ocupava um ambiente aberto, de acordo com comparações com populações de elefantes atuais. Considerou-se a assembléia de mastodontes do Quaternário de Águas de Araxá como uma agregação de unidades familiares, o que sugere um momento de baixa umidade ambiental. Baseados em literatura e nos resultados encontrados, a sua extinção parece ser regional e possivelmente relacionada a um evento catastrófico.