A group of fishermen accidentally discovered the world's first two-headed porpoise, but tossed it back into the sea for fear of getting into trouble.

The bizarre animal was picked up by a Dutch trawler near Hoek van Holland, and is the first known case of conjoined twin porpoises.

Fearing it would be illegal to keep the specimen, the fishermen took a few quick photographs of the dead creature and threw it back into the ocean.

Experts at the University of Rotterdam are now poring over those photographs in the hopes of learning more about parapagus dicephalus - partial twinning - in marine life.