An Aboriginal mission to Europe to negotiate the return of centuries-old artefacts has made a shock discovery in a Berlin museum, uncovering a shield and boomerang that could date from the first encounter between Aboriginal people and James Cook in Botany Bay in 1770.

The crowd-funded team's primary mission was to secure the return of the historic 'Gweagal shield' from the British Museum.

But on the Berlin leg of their journey they stumbled upon an almost identical shield, as well as a boomerang, hidden away in the collection of the city's Ethnological Museum.

The group believes the items in Berlin could have been taken the same day the Gweagal shield was taken from the warrior Cooman, who was shot in the leg in 1770 by Captain Cook's crew when the HMS Endeavour arrived at Botany Bay.

"This is a very positive and historic moment for my people because we just did not know about those items," said Rodney Kelly, a descendant of Cooman and the delegation leader.

"It's of great importance for the people to know about this now, so they can actually know that there are more artefacts there that were taken."

Rodney Kelly believes he is the first Gweagal man to hold the shield and boomerang in 246 years. ( Supplied: Dylan Wood )

First Aboriginal man to hold the shield in two centuries

The group had gone to the Ethnological Museum to look through its collection which contained items from Captain Cook's voyages through the Pacific.

Examining the aged pages of its Aboriginal catalogue from the 18th century, they were stunned to see an entry reading 'Botany Bay 1770'.

Mr Kelly said the museum's curators showed them the items the record related to, a shield and boomerang believed to be made from Red Mangrove and bearing the white ochre hallmarks of Gweagal design.

An 18th century handwritten German catalogue that connects the artefacts to a ship from Botany Bay in 1770. ( Supplied: Dylan Wood )

"The thing that made me sure about the boomerang was the zig-zag lines," Mr Kelly said.

"When Cook and [botanist Joseph] Banks described my ancestors that day, he described them as having zig-zag patterns on them."

Mr Kelly said he believed he was the first Gweagal man to hold the shield and boomerang in 246 years.

"That was a moment, it was sort of sprung on me all of a sudden," he said.

"I was just really proud to be able to hold it and actually see it for the first time, it was very hard to walk away. I didn't want to walk away from it."

Rodney Kelly looking at the catalogue that connected the artefacts to having been brought from Australia. ( Supplied: Dylan Wood )

Artefacts' existence unknown to historians

Mark Wilson, an Australian Institute of Aboriginal and Torres Strait Islander Studies archivist who has been privately supporting the delegation, said it was highly likely the artefacts were taken at the same time as Cooman's shield.

"[Cook's] landing party advanced up the beach to a group of huts where people had vacated quickly," Mr Wilson said.

"Banks' records that they picked up everything that was around the huts, and that was 40 or 50 spears and fishing gigs.

"And although there's no record in the journals from that day of them collecting a shield, certainly there's shields that have been collected."

Rodney Kelly holds the boomerang found at the Berlin museum, believed to have been stolen by James Cook on April 29 1770. ( Supplied: Dylan Wood )

He said the academic literature he had examined so far made no mention of the items held in the Berlin museum, demonstrating how little was known about the thousands of Indigenous artefacts scattered through cultural institutions around the world.

"[This discovery] is a wonderful thing, it's a great thing," Mr Wilson said.

"It's a hard and difficult thing for Indigenous people to connect up to their history, and when artefacts like this show up it's an opportunity to do that.

"I was surprised by the find, I'm surprised by the difficulty of establishing what is in overseas collections.

"There's 6,000 Aboriginal artefacts in the British Museum, and the process of connecting people up with their lost stuff is ongoing."

Cooman and another Gweagal warriors confronting Lt James Cook. ( William MacLeod 1899 )

Mr Kelly said the museum's records showed that the Germans bought the items at an auction in the 1800s.

It is believed that many items from Captain Cook's first voyage to Australia were auctioned off by the funder of the trip, John Montagu, Earl of Sandwich.

Mr Kelly said he was disappointed by the British Museum response to them that it would only loan, but not return the Gweagal shield.

But he said he was encouraged by the Berlin Ethnological Museum's response to the delegation and hopes it will agree to repatriate the items to Australia.