Dinosaur footprints, thought to be about 70 million years old, have been discovered by a geologist working in the north-west Nelson region. The discovery of the first dinosaur footprints ever found in New Zealand and the first evidence of dinosaurs in the South Island has amazed scientists around the world.
Footprints preserved in coastal deposits
The footprints were discovered by geologist Greg Browne of GNS Science while he was investigating the properties of the rock and sediment formations in the north-west Nelson region, near the Whanganui Inlet. The footprints appear in 6 locations over an area of about 10 kilometres. At 1 location, there are up to 20 footprints left by dinosaurs.
The footprints are preserved in coastal deposits from when the area was covered by very shallow intertidal sea water. The prints are roughly circular depressions, with the largest about 60cm in diameter. Most are smaller, typically between 10–20 cm in diameter and were probably formed by dinosaurs 2–6 metres long and weighing several tonnes.
Footprints made by sauropods
After careful investigation, including comparisons with dinosaur footprints in similar aged rocks in other parts of the world, Dr Browne believes the footprints were most likely made by sauropods – large herbivorous dinosaurs with long necks and tails and pillar-like legs.
“What makes this discovery special is the unique preservation of the footprints in an environment where they could easily have been destroyed by waves, tides or wind,” says Dr Browne.
Delicate structures of footprints preserved
The footprints were preserved when the tide came in and quickly filled the original footprints made in sand with soft muddy sediment. Dr Browne says that quite delicate structures were preserved, allowing the scientists to work out which way the dinosaurs were walking, which parts were their heel and toe portions, how soft the sediment was when they moved through the area, how fast they were travelling and how heavy the animals were.
As with much of New Zealand, north-west Nelson was largely submerged under the sea between 20–70 million years ago, and over time, the footprints would have been covered by hundreds of metres of marine sediments.
Then, due to tectonic plate movement, New Zealand was uplifted, and north-west Nelson emerged from the sea. During the past 20 million years, the overlying sedimentary rock has been eroded away to expose the footprints again. Dr Browne says that, amazingly, despite the sinking and re-emergence of the land, the area now is much as it would have been 70 million years ago.
Dinosaurs in New Zealand
While palaeontologists know that dinosaurs were present in ancient New Zealand, which they refer to as Zealandia, the record of their presence is very sketchy.
Dinosaur bones, mostly vertebrae, have been found at only 3 locations – northern Hawke’s Bay, Port Waikato and the Chatham Islands.
Dr Browne’s discovery was published in the December 2009 issue of the New Zealand Journal of Geology and Geophysics.