Research co-author and University of the Otago Palaeogenetics Laboratory director Associate Prof Nic Rawlence believed the foot bone belonged to a bird that was very similar to a bowerbird.
These days, bowerbirds are only found in Australia and New Guinea, but an international collaboration by the University of Otago, the Museum of New Zealand Te Papa Tongarewa and the University of Cambridge shows they may have resided in New Zealand 14-19 million years ago.
"To many people in the world, bowerbirds were made famous by Sir David Attenborough’s nature documentaries and their elaborate courtship behaviours, where males construct an arched structure called a bower, decorated with sticks and sometimes brightly coloured objects like fruit, leaves or even pieces of plastic, all in an effort to attract a mate."
The foot bone found in St Bathans fossil deposits had a close similarity to bowerbirds, particularly "avenue bower builders" that included the brightly-coloured flame bowerbird and the satin bowerbird.
However, the bone specimen found was from a much smaller bowerbird than the living species, Assoc Prof Rawlence said.
"It is smaller than living and extinct bowerbirds, weighing in at 33g, compared to 96g-265g for other species."
The discovery provided a "wonderful and unique" insight into the biological history of New Zealand birds.
Lead author and University of Cambridge Field Palaeobiology Lab researcher Dr Elizabeth Steell said if the bird was a relative of the bowerbirds, it could represent an entirely new songbird family for New Zealand.
"That’s especially significant, given the limited understanding we have of the ancient songbird fossil record in this region.
"The St Bathans bowerbird is the latest songbird lineage to have a long evolutionary history in Aotearoa, where the oldest members of many different groups occur here, including huia, kōkako, tīeke, piopio and mohua.
"It’s likely that all these species represent the descendants of a rapid burst of evolution and dispersal from Australia to New Zealand."
Assoc Prof Rawlence said there were no living descendants of the St Bathans bowerbird left in New Zealand because they would have been particularly susceptible to cooling temperatures before the Ice Ages and the associated changes in forest makeup and distribution.
The foot bone is now stored at Te Papa, in Wellington.
Research was continuing in the fossil grounds of St Bathans, he said.
"This was just one fossil.
"There will be other songbird fossils from the site, and there might be more surprises waiting."
