The fossil darter Macranhinga paranensis (Aves: Pelecaniformes) from the la
te Miocene of Argentina is the largest of all known extinct or living Anhin
gidae. Its body mass is estimated at a mean value of 5.4 kg by using a scal
ing model derived from the logarithmic relationship between measurements of
the least shaft circumference of the femur/ tibiotarsus and body masses. P
redictions of body mass, as well as the analysis of anatomical evidence, ar
e used to infer that Macranhinga paranensis would have probably had a power
ed flapping flight and an aquatic locomotion similar to that of cormorants.
The morphology of the pelvis and the hind-limb would have allowed Macranhi
nga paranensis to catch fishes by means of pursuit-diving rather than stalk
ing them in an anhinga-like manner. As determined by adaptations mainly of
tarsometatarsal morphology, the species had well developed perching and cli
mbing abilities.