Genomics resolves historical uncertainties on phylogenetics and accommodates the systematics of marmosets and Goeldi’s monkey (Primates: Platyrrhini)

Marmosets, with a total of 24 species classified into four genera ( Callithrix , Cebuella , Mico and Callibella ), are the smallest of the anthropoids and one of the most diverse and widespread groups of primates in South America. In contrast, the Goeldi’s monkey ( Callimico goeldii ) is represented by a single species of black, small, fungi-eating primates, endemic to west Amazonia. The phylogenetic relationships of marmoset genera and the phylogenetic position of Goeldi’s monkey, and consequently their systematics, remain uncertain and subject to debate because earlier studies revealed incongruent conclusions. Here we tackle this issue by first reviewing the systematics and the history of phylogenetic studies of marmosets and Goeldi’s monkey. We then explore their phylogenetic relationships by reconstructing a time-calibrated phylogeny using a genome-wide sampling of all lineages of marmosets, tamarins, Goeldi’s monkey, lion tamarins, capuchins, and squirrel monkeys. Our results clearly demonstrate that historical disagreements on phylogenetics and systematics of marmosets are due to incomplete lineage sorting, low phylogenetic signal of morphological and ecological characters, and low sampling at the DNA level. We show that Goeldi’s monkey is a sister lineage to marmosets and suggest that past incongruencies between studies on its phylogenetics and systematics are due to homoplasy of morphological characters traditionally used to infer primate relationships. Accordingly, we accommodate a genus-level classification for marmosets based on a fully-resolved phylogeny and multiple biological traits, redefine the genus Mico , update the definitions of Callibella , Callithrix , and Cebuella , and sediment the family-level classification of Goeldi’s monkey. ### Competing Interest Statement The authors have declared no competing interest.