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We analyzed the geographic variations in the shape and size of the cranium and mandible of two woolly opossums, Caluromys derbianus and Caluromys lanatus. Using geometric morphometrics we analyzed 202 specimens of C. derbianus and 123 specimens of C. lanatus, grouped in 7 and 9 populations, respectively. We found sexual dimorphism in shape variables only in the dorsal view of the cranium of Caluromys derbianus, which is not associated with geographical origin. We detected geographic variation in the size of the mandible in two populations (Nicaragua and Northern Panama), but no geographic variation in shape. The size of the cranium of C. lanatus varies significantly, with clinal variation in peri-Amazon populations, with a break between two populations, Bolivia and Paraguay. Shape analyses also revealed some separation between the Paraná population and all other populations. Our results suggest that the available name, Caluromys derbianus, should be maintained for all individuals throughout the geographic range of the species. The same is true for Caluromys lanatus, which can be separated into two distinct morphologic units, Caluromys lanatus ochropus, from the Amazon and Cerrado, and Caluromys lanatus lanatus, from the Atlantic forest.

Caluromysiops irrupta Sanborn, 1951 is a poorly known didelphid marsupial species, currently known from nine localities in south-central and western Amazonia. Only two records of C. irrupta were known from Brazil. Here we report the third record, in Rondônia state, northwestern Brazil. The specimen was sighted in a well-preserved forest area, in the Parque Estadual Guajará Mirim, Guajará Mirim, Rondônia. Although this record does not represent a distribution extension, it represents an additional record for a very poorly known species.