New isolated petrosals from the Itaboraí beds of Brazil (late Palaeocene or early Eocene) are here described and referred to the early diverging litoptern Miguelsoria parayirunhor, based on phylogenetic, size, and abundance arguments. Both the external and internal anatomy of these specimens were investigated, which for the first time document many details of the auditory region of a Palaeogene litoptern. Our cladistic analysis, which included our new observations, failed to recover a monophyletic Litopterna but did not exclude it. A constrained analysis for the monophyly of this order showed that several features such as a (sub)quadrangular and anteroposteriorly elongated tensor tympani fossa and a large notch in the vicinity of the external opening of the cochlear canaliculus may constitute synapomorphies for Litopterna. The evolution of several other auditory characters amongst Litopterna is discussed and the relative dimensions of the inner ear and surrounding petrosal in the group were also investigated. This allowed detection of negative allometry of the bony labyrinth within the petrosal, which was confirmed by measurements and regression analysis across a larger sample of placental mammals. This scaling effect probably has an important influence on several characters of the bony labyrinth and petrosal, amongst which are the length of the vestibular aqueduct and cochlear canaliculus. It demonstrates that many aspects of the morphological variation of the bony labyrinth need to be thoroughly investigated before being incorporated into phylogenetic analyses.  © 2015 The Linnean Society of London

-TAPHONOMY OF THE FOSSIL MAMMALS ASSEMBLAGE OF THE "1968 FISSURE", SÃO JOSÉ DE ITABORAÍ BASIN, RIO DE JANEIRO STATE, BRAZIL. Significant amount of taxonomic information has beenextracted from fossil mammal assemblages of the São José de Itaboraí Basin, located at Rio de Janeiro State, Southeastern Brazil. However, taphonomic analysis, which are important for understanding the formation of these taphocoenosis, are rare and superficial. A limestone fissure excavated in 1968 (here called "1968 Fissure") stands out among the several known fossiliferous concentrations by its abundance of skeletal elements and by the unique brownish color of the specimens, which differentiate them from those collected in other fissures. This study aims to identify and interpret taphonomic features observed in the taphocoenosis "1968 Fissure", which include fractures, abrasion marks, desiccation marks, teeth marks, bone representativeness, and preservational patterns diagnostic for the occurrence and type of transport during the formation of fossiliferous concentration. Based on taphonomic analysis, the mammal taphocoenosis of the "1968 Fissure" is characterized as parautochthonous, being exposed for a short time before being deposited in the fissure after a short transport, possibly triggered by floods. Probably, predators did not influence the formation of the fossil assemblage studied. Only small mammals occur in the fissure due to a possible selection during the bioestratinomic phase. During the fossildiagenetic phase, several fractures were produced in the material due to compression generated by sediment deposition in the fissure. The observed pattern in the skeletal completeness shows the influence of anatomical features of mammals in differential preservation of skeletal remains during the process of fossilization.Key words: taphonomy, "1968 Fissure", São José de Itaboraí Basin, mammals, Itaboraian mammal age.RESUMO -Quantidade significativa de informações taxonômicas tem sido extraída das assembleias fossilíferas de mamí-feros da bacia de São José de Itaboraí, situada no Estado do Rio de Janeiro. Porém, análises tafonômicas, importantes para o conhecimento da formação dessas tafocenoses, são raras e superficiais. Dentre as várias assembleias fossilíferas desta bacia destaca-se a procedente de uma fenda escavada em 1968 (denominada "Fenda 1968"), pela abundância e pela coloração marrom dos elementos esqueletais, que os diferencia dos fósseis procedentes das demais fendas. Este estudo tem como objetivo a identificação e interpretação de feições tafonômicas observadas na tafocenose da "Fenda 1968", as quais incluem fraturas, marcas de desgaste, de dentes e de dessecação, representatividade óssea, além de padrões preservacionais diagnós-ticos para a ocorrência e o tipo de transporte durante a formação desta concentração fossilífera. Com base na análise tafonômica, a tafocenose da "Fenda 1968" caracteriza-se como parautóctone, tendo ficado exposta por pouco tempo antes de ser depositada no interior da fenda por um curto tr...

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A new small species of Eocaiman is described on the basis of three anterior left mandibular rami and one isolated tooth. The specimens came from the middle-upper Paleocene Itaboraı ´Basin (Rio de Janeiro State, Brazil; Itaboraian South American Land Mammal Age). The new taxon differs from the other two Eocaiman species, such as its small size, likely participation of the splenial in the mandibular symphysis, a reduced angle between the longitudinal axis of the symphysis and the mandibular ramus, and enlarged ninth and tenth dentary teeth (in addition to the large first and fourth dentary teeth). The participation of the splenial in the mandibular symphysis is a unique character among caimanines (with the only possible exception being Tsoabichi greenriverensis). The new taxon provides new information on the taxonomic and anatomical diversity of the genus Eocaiman, a taxon of prime importance to understand the evolutionary origins of caimans given its position as the basalmost member of Caimaninae. Furthermore, the new taxon has a relatively small body size in comparison with other species of Eocaiman, a case paralleled by other Itaboraian reptilian groups (e.g. snakes), suggesting that this ecosystem provides critical data to test the relationship between reptilian body size and climate. http://zoobank.org/83636F22-D121-4A77-9141-BE68987B6CBF