Flightless rails scurried around Central Otago up to 19 million years before the takahe and the weka roamed New Zealand’s forests.
A Flinders University-led team of Australian and New Zealand scientists have discovered that numerous bones found in 19 to 16 million-year-old sediments near St Bathans in Central Otago are those of two new species of tiny flightless extinct rails. They are thought to be the oldest flightless rails known globally. The two new species are miniscule in relation to today’s rails. One is barely larger than a sparrow.
The new research led by palaeontologists from Flinders University with colleagues from University of NSW, Canterbury Museum and the Museum of New Zealand Te Papa Tongarewa is published today in the Journal of Systematic Palaeontology.
Rails, birds in the Rallidae family, include pukeko and coots and are usually seen around wetlands. Many rail species fly and have dispersed to far-flung oceanic islands. But rails have often evolved into flightless forms on islands, more so than any other bird group. The world’s largest flightless rails evolved in New Zealand, notably the takahe and weka.
A 5,600 km2 megalake – Lake Manuherikia - dominated New Zealand’s South Island 19–16 million years ago. It was surrounded by a subtropical rainforest of plants typical of Australia and long lost from New Zealand. Gum trees, sheoaks, palms and cycads were common. Today traces of this giant lake are revealed in sediments around the town of St Bathans.
“Flightlessness in birds is often associated with an increase in size,” says Ellen Mather, lead author of the study and a PhD student at Flinders University. “The weka, which is in the same family as our fossil birds and lives in New Zealand today, is about the same size as a chicken. The Banded Rail, the weka’s closest flying relative, is about half that size.”
The most common of the new fossil rails, which has been named Priscaweka parvales, meaning ancient weka with small wings, was a mere one twentieth of the weight of a weka and similar in size to the recently extinct Chatham rail Cabalus modestus.”
Small flightless birds only exist in the absence of terrestrial mammal predators. New Zealand has long been upheld as the iconic example of an avifauna evolved in the absence of such mammals. When humans discovered New Zealand, the main islands had many flightless birds including giants such as the nine species of moa, two giant geese, two adzebills, even some tiny wrens, and at least five flightless rails.
Dr Paul Scofield Senior Curator Natural History at Canterbury Museum who participated in the research said "The new St Bathans’ rails join a host of other fossil birds recovered from these deposits that show New Zealand has long been a land of birds. The discovery of these two miniscule flightless rails raises the question, ‘Where did they come from?’. The new species are unlike any rail known elsewhere so their exact origin or closest relatives remain a mystery.”
Alan Tennyson of Te Papa, a co-author of the new study, says “This fossil rail discovery reinforces New Zealand’s importance in understanding the evolution of birds worldwide and we are sure that many more important fossil discoveries will be made at this site.”
Other than hints of large flightless moa ancestors these rails are the first flightless birds to be confirmed from the St Bathans fauna. Flightless birds have been a feature of the New Zealand avifauna for millions of years longer than generally thought.
“The ongoing research into the fossil birds of New Zealand builds on that begun over 150 years ago. It continues to throw up revelations into the timing and origins of major groups of birds that characterise modern avifaunas” said Associate Professor Trevor Worthy of Flinders University, Adelaide.
Professor Mike Archer of the PANGEA Research Centre, UNSW, Sydney said “This new discovery emphasises the fact that New Zealand has long been one of the world’s most extraordinary engines driving bird evolution. Charting how lineages like these rails have changed through time on an island that has been geographically isolated for over 60 million years will test basic presumptions made about bird evolution in general.”
To cite this paper: Mather EK, Tennyson AJD, Scofield RP, De Pietri VL, Hand SJ, Archer M, Handley WD & Worthy TH. 2017. Flightless rails (Aves; Rallidae) from the early Miocene St Bathans Fauna, Otago, New Zealand. Journal of Systematic Palaeontology. doi/full/10.1080/14772019.2018.1432710