When Sir David Attenborough opens the University of Cambridge’s zoology museum this week, the proud curators will show him their fabulous discovery.

It’s fair to say the casual visitor might wonder why they are so excited by the scruffy frame containing a few cobwebby grey-brown wisps, discovered during a £4.1m redevelopment of the museum.

However, the scientists are convinced the battered label, which reads “Feathers of Moa”, is correct and the wisps are the remains of huge flightless birds, some standing three metres tall, that were hunted to extinction more than 600 years ago after Polynesian people settled in New Zealand.

The museum’s collection holds about two million objects – “nobody is quite sure, there really are an awful lot of very small insects,” said museum manager Jack Ashby – all of which had to be moved to temporary storage, their condition checked, and returned to the displays or the gleaming new stores.

Stuart Turner, a technician, found the feathers at the back of an old cupboard, read the faded label, and took them to the curators. If a DNA test confirms the feathers are indeed of the moa, they will be a major addition to the fossil bone evidence for the unfortunate creatures, which, like the dodo, proved disastrously edible.

Facebook Twitter Pinterest ‘Feathers of Moa’: one of the incredible rare discoveries from the museum’s redevelopment. Photograph: University of Cambridge

The museum’s new entrance hall is dominated by the 21 metre (69ft) skeleton of a fin whale, a creature Ashby knows well. When he studied in the same building as an undergraduate, the whale was suspended from the concrete roof over an open air piazza, where it survived as a pigeon roost for 45 years. Every inch was cleaned before it could be moved indoors, and it is in remarkably good condition considering its eventful afterlife.

The whale was beached at Pevensey in 1865 and bought by a showman, who somehow moved it to the cricket ground at Hastings and let the public in for sixpence a head (children half price). As Ashby points out, the visitors must have had strong stomachs: an archive photograph clearly shows that the huge carcass had started to bloat and decompose.

The displays include many other extinct creatures, including a sloth that stood as tall as a giraffe. One of Ashby’s favourites is the diprotodon, a cousin of the wombat as big as a rhinoceros. It too is believed to have been hunted to extinction: with its enormous body carried on tree-trunk sized legs, one diprotodon was a lot of meat.

Coiled up in a jar there is a small octopus, believed to have been kept as a pet by Charles Darwin on HMS Beagle. He wrote excitedly to London about watching it changing colour, thinking it a new discovery. His mentor John Stevens Henslow replied kindly that he had reported the phenomenon himself, “but not in such perfection as you seem to have done”.

Hundreds of the objects are on display for the first time, but many marvels remain in the stores, including an antique wooden crate neatly labelled “a selection of dried hearts and stomachs etc”.

Attenborough has described the museum as of the highest importance – “a place where the public can come to see, study and wonder”.

Prof Paul Brakefield, director of the museum, which is still a teaching collection as well as a free public resource, said he would be excited to open the doors on 23 June. “Museums like ours play such an important role in inspiring awe and excitement in the natural world, as well as helping to answer genuinely world-changing challenges like climate change and biodiversity loss.”