Rare Fossil Goose Discovery Rewrites New Zealand's Avian Evolution

The discovery of a rare fossil goose in an ancient Central Otago lake indicates that the evolutionary history of Aotearoa New Zealand birds is more dynamic than previously understood. Researchers from the University of Otago, Te Papa Museum, and the University of Cambridge collaborated on a paper analyzing the fossil and its origins, published in the journal Historical Biology.

A New Ancient Species Unearthed

The research team re-examined bones previously identified as belonging to geese from fossil deposits around St Bathans. This analysis led to the identification of an undescribed species, comparable in size to a small goose. The newly identified species was named Meterchen luti, a reference combining ancient Greek for "mother goose" and Latin for "of the mud," signifying its ancient origins from fossil deposits.

It was determined that the St Bathans goose is not closely related to the recently extinct giant flightless New Zealand geese (Cnemiornis species) or their Australian relative, the Cape Barren goose.

This finding, alongside other recent genetic research, suggests a more complex evolutionary pathway for New Zealand's bird species.

Challenging Previous Theories

An earlier theory proposed that the St Bathans goose represented the direct ancestors of Cnemiornis geese, suggesting a lineage of at least 14 million years in Zealandia. However, this conflicts with genetic evidence indicating that the ancestors of Cnemiornis arrived from Australia approximately seven million years ago. The recent reassessment of the fossil records supports the later arrival theory.

Dynamic Evolution in Zealandia

While the ancestors of the St Bathans goose arrived in Zealandia prior to 14 million years ago, no descendants from this specific lineage survived. The use of both DNA and fossil evidence provides a detailed reconstruction of how Zealandia's geological, climatic, and human history has shaped the evolution of its fauna. The relatively recent evolution of the giant flightless Cnemiornis geese, which grew to one meter tall and weighed up to 18kg, serves as an example of rapid morphological change possible on islands within a short timeframe.