The Sint Pietersberg hill near Maastricht has yielded the oldest undocumented bird skull in the world, the city’s natural history museum has announced.

The fossil parts containing the bird’s skull and other skeleton parts, found by Maarten van Dinther from Leiden University in 2000, were only recently sent to Cambridge University in Britain for further analysis. A high resolution CT scan revealed a hitherto unknown bird species, the Asteriornis maastrichtensis, which dates back 66.7 million years.

‘The eagle eye of Maarten van Dinther has given us a fantastic gift, this is a world first,’ a jubilant John Jagt, palaeontologist at the museum, said.  ‘I bounced up and down when I saw the first images of our cretaceous chick!’

The fossil is important because it gives insight into the earliest stages of the evolution of modern birds. It is closely related to a common ancestor of the group that now comprises chickens, ducks and geese, or Galloanserae, Jagt said.

The new species combines both chicken and geese-like characteristics and has been dubbed the ‘Wonder chicken’.

A comparison with modern birds suggests that Asteriornis weighed about 390 grams and that it may have lived along the edges of the subtropical sea which covered the area at the time. Contrary to the group of fish eating birds, the newly discovered species had no teeth.

The fossil is an unusual find in that bird skeletons are very brittle and don’t fossilise easily, Jagt said.

A large 3D print of the find, which has been described in prestigious journal Nature, will go on show at the museum once it reopens, the museum said. The museum is currently closed because of the Coronavrus crisis and the fossils will remain in Cambridge until the final stage of the research has been concluded.

The Sint Pietersberg’s cretaceous layers have been a fossil hunting ground for the last 250 years. Small snails, sea urchins, crabs, corals, and various species of fish are common finds but palaeontologists have also found parts of a Mosasaurus skeleton and sea turtles which inhabited the shallow and warm sea around 68 and 66 million years ago.