Here we report the first record of genus Cryptonanus in the state of Rio de Janeiro, Brazil. One specimen (MZUSP35409) was captured in an Atlantic Forest fragment and was identified by morphological characters and molecular analysis using cytochrome‑b (MT-CYB) and von Willebrand Factor (VWF). Phylogenetic reconstructions based on VWF sequences positioned our specimen into the genus Cryptonanus, and the shortest genetic distance of MT-CYB was estimated between our specimen and an undescribed specimen from Piauí. Our record increases the genus’ geographic range approximately 350 km from Cotia and Ibiúna municipalities, São Paulo. The genus Cryptonanus remains taxonomically poorly understood.

Capítulo 3 Mamíferos em um fragmento de floresta Atlântica semidecídua: avaliação de riqueza, abundância e densidade por censos diurnos.