Auckland pipeline upgrade unearths fossil treasure trove

A huge and diverse hoard of 300,000 Pliocene fossils has been unearthed in Auckland, New Zealand as part of excavations for a major sewage pipeline upgrade.

Palaeontologist Dr Bruce Hayward describes the find, dating between 3.7 and 3 million years old, as “the richest deposit of fossils of this age in New Zealand”.

The diverse material includes fossil species from land and coastal environments, from rocky shores, estuaries, shallow flats and embayments, all likely swept to the site millions of years ago by tidal currents or washed down streams into the sea.

“So when all those different fossils from all those different environments have been brought together, we ended up with a species list at the finish of 266 species, after all that collecting,” he says.

Amongst the fossils are at least ten new, previously unknown species of mollusc which will be described and named in future work.

The treasure trove – located in Auckland suburbia between the city and the airport – was   uncovered when water and wastewater company, Watercare, began digging a set of 30 metre wide and 40m deep shafts at the site of Māngere Wastewater Treatment Plant as part of the wastewater infrastructure upgrade in 2020.

Interested in learning more about the age of shell beds known to be located underneath the site, Hayward asked the contractors if they could collect some fossil samples from the excavation. 

Early finds of incredibly well-preserved fossils soon indicated the scientific significance of the site.

To enable Hayward and palaeontology enthusiasts to better examine the material, the company began stockpiling the excavated material in a nearby paddock, and later funded two graduate students to work for 6 months with the Auckland War Memorial Museum to search through and analyse the material.

The majority of the fossils found at the site are shells from bivalves or gastropods from shallow marine and intertidal environments. But the haul also includes rare finds like baleen whale vertebrae, sharks’ teeth, rare specimens of coral, and bones from eagle rays. 

Most of the fossils were found at depths of 35 – 40m within the Māngere shellbed.

The finds also include the world’s oldest known specimens of flax snails, the ancestors to New Zealand’s iconic modern flax snails.

“Prior to this find, the oldest were on Lord Howe Island at 100,000 years. These are 3 million years old,” says Hayward.

Around 5000 of the best specimens have been retained by the Auckland Museum for the benefit of the public and ongoing research. 

The details are published in the New Zealand Journal of Geology and Geophysics and dedicated to Dr Alan Beu, New Zealand’s leading molluscan fossil expert, who was working on the fossils when he passed away earlier this year.

Hayward says many of the fossils reveal information about the ancestors of species common in New Zealand before the Europeans came. 

The significant fossil find may also help scientists understand the future in the context of climate change, he says.

“The assemblage tells us more about the past temperature of the sea at that time, which is quite a lot warmer than we’ve got now. But what we’re heading for probably by the turn of the century, so we’re looking at what the conditions may be like, around Auckland, in about 2100.”