Mexican officials say fishermen have found two conjoined gray whale calves in a lagoon in Baja California.
A government biologist, Benito Bermudez, said the whales were found alive in the Ojo de Liebre lagoon but died shortly after being born.
He said they were linked at the waist, with two full heads and tail fins.
Every year, thousands of gray whales swim south from the US state of Alaska to warmer waters in Mexico where they mate and give birth.
Mr Bermudez, who works for Mexico’s National Natural Protected Areas Commission, or CONANP, described the discovery as “exceptionally rare”.
“It’s the first record we have of this event in the history of whale censuses we’ve conducted since 1985,” he told the EFE news agency.
He said scientists were collecting skin, muscle and baleen samples to study the creatures.