Moa footprints discovered in Ōtākou/Otago date about 3.6 million years ago, researchers said on Wednesday.
That makes them the second-oldest moa traces or fossils ever found.
It comes after Ranfurly man Michael Johnston discovered the seven fossilised prints in 2019, in the bed of the Kyeburn River in Maniototo.
Kane Fleury, natural science curator at Tūhura Otago Museum, said the four-year process of studying the moa prints was "incredible".
“Conditions had to be absolutely perfect for these tracks to be preserved and they had to be just right again to expose the fossils without destroying them."
Scientists got to work after Johnston asked the museum about the prints.
Word got out quickly and international media were interested.
"The public really got on board with how spectacular this find was and had heaps of questions, so it’s a great feeling to be able to follow up with some answers," Fleury said.
He said the high community interest helped drive the research.
“The project really captured people's imaginations."
A paper published in the Journal of the Royal Society of New Zealand shed some light on the moa prints.
Most of them were likely from an 84kg bird from the Pachyornis genus, standing 109cm tall at the hip, the researchers said.
The Pachyornis genus includes the heavy-footed moa, Mantell's moa and crested moa - meaning it was probably one of these three species.
Using cosmogenic nuclide dating, scientists could estimate when the sediment was buried or exposed, determining that it was about 3.6 million years ago.
They said the moa had already evolved to their gigantic size by the time they walked through the Maniototo riverbed all those years ago.
And surprisingly, when the researchers began investigating the riverbed, they found a faint print from a 158kg bird - likely a moa nunui (South Island giant moa) or a kuranui (North Island giant moa).
Fleury said most remains or traces of moa are less than 10,000 years old but the Maniototo prints gave hints about moa evolution.
"We've cracked that door open a bit more," he added.
Ian Griffin, director at Tūhura Otago Museum, said it was important mahi despite not receiving Government funding.
"We linked up with experts from NZ and elsewhere and assembled a team that carried out one of the coolest and most important fossil recoveries in recent times.
"I'm stoked to see what's come of that."
