| Summary: | The family Oceanitidae, formerly considered a subfamily of Hydrobatidae, includes all the small storm-petrels of the southern hemisphere. The ancestor-descendent relationships and evolutionary history of one of its genera, Oceanites, have been partially studied, yielding contrasting results. We revised the phylogenetic relationships of this group using Bayesian inference (BI) based on new sequence data of the mitochondrial gene Cytb and linear morphological measurements of all species and five subspecies-level taxa in Oceanites, including a new taxon from the Chilean Andes. Our BI results show that the Oceanites genus is monophyletic and composed of four well-supported clades (posterior probability > 0.95): (1) chilensis; (2) exasperatus; (3) gracilis, pincoyae, and barrosi sp. nov.; and (4) oceanicus and galapagoensis. The species O. chilensis is a basal clade within Oceanites. According to our time-calibrated tree, the split between Oceanites and the other genera in Family Oceanitidae is estimated to be ~35.9 Mya, and the oldest divergence within Oceanites (the split between O. chilensis and other Oceanites) was dated to the early Miocene, around c. 21.3 Mya. The most probable geographic origin of Oceanites is the Southern Ocean. The morphological data suggest continuous size variation between Oceanites taxa, ranging from smallest in gracilis to largest in exasperatus. Based on our phylogenetic hypothesis, and morphological analyses, we suggest elevating to species status the taxa galapagoensis, chilensis, and exasperatus, and we describe a new taxon barrosi sp. nov., thus recognizing a total of seven species within the genus Oceanites.
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