a) The extinct animal has been described through re-examination of a specimen that's been in a museum collection since 1951.
c) Researchers think it is a relative of the endangered South Asian river dolphin, offering clues to the evolutionary history of modern species.
d) The findings have been published in the journal open access Peer J.
e) The fossil, a partial skull about 22cm (9ins) long, was discovered in south eastern Alaska by geologist Donald J Miller in 1961.
b) It then spent decades in the collection of the Smithsonian Museum of Natural History in Washington DC.
