Scientists have revealed that there is not one but two types of killer whale living in UK waters.

Each differs in its appearance and diet, with males of one type being almost two metres longer than the other.

The killer whales could be at an early stage of becoming two separate species, the researchers say.

The international group of scientists has published its results in the journal Molecular Ecology.

"It's exciting to think about two very different types of killer whale in the waters around Britain," says Dr Andy Foote from the University of Aberdeen, UK, who undertook the study.

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