Meet the ‘Old Mother Goose’ from NZ’s subtropical prehistoric past

During the early to mid Miocene period, 14 to 19 million years ago, a vast lake covered much of what is now Central Otago.

Along the shores of Lake Manuherikia, whose remnants are found near present-day St Bathans, lived crocodilians, turtles, and bowerbirds, as well as early relatives of bats, moa and kiwi, and a rich diversity of waterfowl such as ducks and swans.

This lost ecosystem is known today from the famous St Bathans fossil deposits, which preserve one of the world’s richest records of the Miocene and offer a rare window into Aotearoa’s warmer, more subtropical ancient past.

Our newly published research adds another waterfowl species to this remarkable menagerie. It also sheds important new light on the origins of New Zealand’s recently extinct giant, flightless geese of the genus Cnemiornis.

NZ’s long-lost waterfowl

Spanning 5,600 square kilometres, Lake Manuherikia was ten times the size of New Zealand’s Lake Taupo. It was a dynamic habitat that supported a diverse range of waterfowl, including five stiff-tailed ducks, one swan, two shelducks, one dabbling duck and our new goose.

While many of these waterfowl are incredibly common in the fossil deposits around St Bathans, others, including the largest species, are quite rare.

Our team reexamined the remains of all the bones previously identified as belonging to geese. We then compared them with other large waterfowl bones from the deposits and a broad collection of comparative bird skeletons housed in the Museum of New Zealand Te Papa Tongarewa.

We determined that the bones included an undescribed species the size of a small goose.

We named our new bird the St Bathans goose Meterchen luti, as a play on the nursery rhyme “Old Mother Goose”. In our case, an ancient goose rises up out of the mud of the fossil deposit. Meterchen means “mother goose” in ancient Greek, while luti is Latin for “of the mud”.

With ten unique species of waterfowl now described from the fossil deposits, across a range of sizes, Lake Manuherikia was clearly a very productive and dynamic lake system, supporting a large and complex ecosystem.

Not as ancient as first thought

Our St Bathans goose is only based on fragmentary remains but there is enough preserved to show that it is not a close relative of the giant flightless Cnemiornis geese, nor their Australian cousin, the Cape Barren goose Cereopsis novaehollandiae.

Recent genetic research is showing the evolutionary origin of New Zealand’s birds is more dynamic than previously thought, with influxes from Australia, South America, the Northern Hemisphere and places unknown.

Throughout geological history, many birds arrived in Zealandia, the now-mostly submerged continent that includes New Zealand. But the ancestors of some of our large birds only arrived here surprisingly recently – in the past 4-5 million years – including takahē, the Eyles or Forbes’ harrier and the giant Haast’s eagle.

An earlier theory argued that the St Bathans goose represented the direct ancestors of giant flightless Cnemiornis geese, implying this lineage had been present in Zealandia for at least 14 million years.

However, this conflicts with genetic evidence suggesting the ancestors of Cnemiornis arrived from Australia only 7 million years ago, which proponents of the earlier theory discarded.

Our reassessment, based on a much broader set of comparative bird skeletons, rather than single exemplars, does not support the earlier-arrival hypothesis and instead supports the later arrival.

Turnover and transformation

Increasingly, our multidisciplinary research is showing that there have been considerable levels of biological turnover throughout Zealandia’s history.

While the ancestors of the St Bathans goose no doubt arrived in Zealandia earlier than 14 million years ago, no descendants survived, with the ancestors of the giant Cnemiornis geese colonising much more recently, only for their descendants to go extinct shortly after human arrival due over-hunting and predation.

The relatively recent evolution of the giant flightless Cnemiornis geese offers another striking example of the rapid morphological change that can occur within a short timespan on islands, where evolution can run rampant. At one metre tall and weighing up to 18kg, these were the largest geese in the world.

By using all the scientific tools in the toolbox, we can reconstruct how the dynamic geological, climatic and human history of Zealandia has shaped the evolution of Aotearoa’s fauna in ever more detail.

Each new discovery is a reminder that the story of New Zealand’s birds – and of Zealandia itself – is very much still being written.