A giant goose-like bird that was the size of a light aircraft and had a beak like a crocodile’s jaws has been found to have soared above Britain 50 million years ago.

A fossil skull preserved in London clay has been identified as belonging to a relative of modern ducks and geese with a wingspan of 5m (16ft) and armed with a beakful of teeth. The ancient creature has been nicknamed Mother Goose by Gerald Meyr, the palaeontologist who identified it, because of the bird’s extraordinary size.

It is thought to have had a similar lifestyle to the albatross of today, which spends most of its life at sea and is a master at using thermals and air currents to remain airborne with minimum effort.

The ancient goose, one of the biggest species of bird to take to the skies, was even bigger than the wandering albatross, which, at up to 3.7m wing tip to wing tip, has the biggest wingspan of all living birds. Mother Goose, more properly named Dasornis emuinus, is thought to have had a wingspan almost 50 per cent bigger than the wandering albatross.

“Imagine a bird like an ocean-going goose, almost the size of a small plane,” said Dr Meyr, of the Senckenberg Research Institute and Natural History Museum in Frankfurt. “They had lightweight bones so despite their great size they weren’t very heavy. I think they were capable of soaring and gliding – though they would probably have needed strong winds to take off.

“By today’s standards these were pretty bizarre animals, but perhaps the strangest thing about them is that they had sharp, tooth-like projections along the cutting edges of the beak.

“The beak was so covered in bony teeth that it looked like a crocodile.”

Some early birds had enamel teeth but these were lost about 100 million years ago, yet Mother Goose reevolved them, this time made from bone and possibly covered with a layer of keratin, the biological material used for the beak. Dr Meyr believes that the 60 to 80 teeth in the beak, estimated at 20-25cm long, were developed to help the prehistoric bird keep a grip of the fish and squid it would have snatched from the sea.

“No living birds have true teeth – which are made of enamel and dentine – because their distant ancestors did away with them more than 100 million years ago, probably to save weight and make flying easier,” he said.

“But the bony-toothed birds, like Dasornis, are unique among birds in that they reinvented tooth-like structures by evolving these bony spikes.

“It’s linked to diet. These birds probably skimmed across the surface of the sea, snapping up fish and squid on the wing. With only an ordinary beak these would have been difficult to keep hold of, and the pseudo-teeth evolved to prevent meals slipping away.”

The fossil skull was found in clay on the Isle of Sheppey and in its day the bird would have cruised above the waters covering what is now Essex, Kent and London.

When the bird died it sank to the bottom of the sea, where it was preserved after becoming covered in sediment. It was discovered about five years ago by a private collector but has only now been fully analysed, and the findings reported in the journal Palaeontology. Although the bird had a similar lifestyle to the albatross, analysis of its remains has shown that its closest relatives, living or extinct, are ducks and geese.

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