An Otago man out for a walk made a significant palaeontological discovery.
It was a ripper of a day, and Michael Johnston, a tractor driver from Ranfurly, thought the dogs could use some cooling off, so they went down to the Kyeburn River for a dip. In the shallows, something caught Johnston’s attention: a giant footprint sunk into the clay. Then another, and another, continuing into the water. Each was the size of a dinner plate: 30 centimetres by 30 centimetres.
Johnston sent photos via Facebook to the Otago Museum, and natural science assistant curator Kane Fleury visited with a wetsuit, snorkel and waterproof camera. The footprints were submerged about a metre deep. Fleury knew immediately that they were important and they needed to be rescued as soon as possible. These were moa footprints, millions of years older than all other known moa footprints, and the only ones found in the South Island.
Several million years ago, a moa walked carefully across a muddy river flat, leaving prints in the clay and silt. After these had hardened slightly, they were covered by more layers of river silt, then buried under millions of years of clay and soil.
Until last summer. Heavy rain and floods in the Kyeburn carved away the river bank, exposing the harder clay layer—and, luckily, someone noticed. A rainier summer and the river would have scoured out the trackway. The prints are in clay that can be dented with a finger and that breaks easily, so they needed to be taken out in sections, rather than as one giant slab.
The removal was done with the full support of iwi but still took months of planning and resource consents, all while the river was slowly eroding the prints away. The river was diverted, the water pumped out, and the prints cut from the clay with a chainsaw.
Everything had to be done in secrecy, in case someone else stumbled across the prints and decided to hack one out and sell it on Trade Me rather than tell a museum.
When trackways like these were discovered in the 19th century, people would take photographs and try to make plaster casts. These days, drones with cameras do photogrammetry, creating a 3D model of the entire site before it’s excavated. Next, Otago Museum will 3D-scan the prints, then slowly dry them over months and stabilise the surface, so that they can be put on display.
If circumstances had been slightly different—an unseasonal flood, or dogs that just wanted to swim somewhere else—the prints would have been destroyed or never discovered. How many other treasures like this are still waiting to be uncovered?