LAUSR

ABSTRACT We describe a new specimen attributed toMacranhinga ranzii, a taxon whose holotype is a left femur, being collected from rocks in the Solimões formation, Southwestern Amazon. The new material is an almost complete pelvic girdle and synsacrum (UFAC 6471), collected in a new fossiliferous locality named Cajueiro. The compatibility between the diameter of foramen acetabuli of UFAC 6471 with the caput femoris of the holotype and the synapomorphies present in the specimen allowed us to attribute it to M. ranzii and emend the diagnosis for this species. Based on three linear measurements of the pelvic girdle and the medium weight of extant Anhinga, we estimate the adult animal’s body mass at 8.6 kg. The phylogenetic inference resulted in two equally probable evolutionary hypotheses: one of them with a monophyletic Macranhinga and in the other Meganhinga chilensis as the sister clade of a Macranhinga (in part) plus Anhinga clade. In both scenarios, Macranhinga ranzii is closely related to G. kiyuensis. The morphological and myological data gained in this study enabled us to recognise Macranhinga ranzii as a proficient swimmer and diver, and consequentially a skilled fish hunter in deep waters.