The squirrel monkey, Saimiri, is a pan-Amazonian Pleistocene radiation. We use statistical phylogeographic methods to create a mitochondrial DNA-based timetree for 118 squirrel monkey samples across 68 localities spanning all Amazonian centers of endemism, with the aim of better understanding (1) the effects of rivers as barriers to dispersal and distribution; (2) the area of origin for modern Saimiri; (3) whether ancestral Saimiri was a lowland lake-affiliated or an upland forest taxa; and (4) the effects of Pleistocene climate fluctuation on speciation. We also use our topology to help resolve current controversies in Saimiri taxonomy and species relationships. The Rondônia and Inambari centers in the southern Amazon were recovered as the most likely areas of origin for Saimiri. The Amazon River proved a strong barrier to dispersal, and squirrel monkey expansion and diversification was rapid, with all speciation events estimated to occur between 1.4 and 0.6Ma, predating the last three glacial maxima and eliminating climate extremes as the main driver of squirrel monkey speciation. Saimiri expansion was concentrated first in central and western Amazonia, which according to the "Young Amazon" hypothesis was just becoming available as floodplain habitat with the draining of the Amazon Lake. Squirrel monkeys also expanded and diversified east, both north and south of the Amazon, coincident with the formation of new rivers. This evolutionary history is most consistent with a Young Amazon Flooded Forest Taxa model, suggesting Saimiri has always maintained a lowland wetlands niche and was able to greatly expand its range with the transition from a lacustrine to a riverine system in Amazonia. Saimiri vanzolinii was recovered as the sister group to one clade of Saimiri ustus, discordant with the traditional Gothic vs. Roman morphological division of squirrel monkeys. We also found paraphyly within each of the currently recognized species: S. sciureus, S. ustus, and S. macrodon. We discuss evidence for taxonomic revision within the genus Saimiri, and the need for future work using nuclear markers.

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Saimiri collinsi is a primate that occurs in the Amazon biome and recently was elevated to species status. Despite being an abundant and widespread species, S. collinsi distributional limits are still unknown in the transitional region between Amazon and Cerrado biomes. Here we provide 25 new records for the species, obtained through field observation and analysis of museum specimens. Twenty-one records are from Maranhāo state, three from Tocantins where the species had not yet been registered and one in Pará state. These records expand its known distribution, which now includes the area of transition between the Amazon and Cerrado, as well as one record in the Cerrado biome. We registered the species in areas with intense forest fragmentation and within different habitat types, including primary and secondary forest, babassu palm forest and capoeira forest. This indicates that S. collinsi is a species that can survive in locations with extreme anthropogenic alterations. Nevertheless, out of these new records only the ones in Maranhāo are within protected areas. Even these protected areas are undergoing pressures from deforestation, agriculture, livestock and mining, suggesting that these squirrel monkey populations might be threatened in this region.

A cuíca Marmosa demerarae é uma espécie onívora, que se alimenta principalmente de insetos e frutos. O conhecimento sobre a história natural dessa espécie ainda é incipiente. Existe apenas um registro de M. demerarae alimentando-se de vertebrados na literatura, tendo este sido causado por interferência humana no ambiente. Nesta nota, nós reportamos o primeiro registro de predação do lagarto Norops fuscoauratus por M. demerarae, que foi realizado no município de Barcarena, Pará, Brasil. Este registro é relevante para incrementar o conhecimento sobre a ecologia alimentar de M. demerarae na Amazônia.