A 62-million-year-old partial fossil skeleton suggests that tropicbirds – seabirds found across the Atlantic, Pacific and Indian Oceans – originated in the ancient continent Zealandia, now submerged in the Pacific Ocean.
The find was unearthed at the Waipara Greensand rock unit on New Zealand’s south island, about 50 km north of Christchurch. The specimen includes a nearly complete skull, wing, pelvis and other small, fossilised fragments. It is the second fossilised tropicbird found from the area with an earlier smaller, unnamed tropic bird specimen found in 2016.
Today, there are three species of tropicbird: red-billed, red-tailed and white-tailed tropicbirds.
Tropicbirds have a long evolutionary history with fossils of today’s extant species found dating to the Palaeocene (66–56 million years ago; after the extinction of the non-avian dinosaurs) and Eocene (56–34 million years ago) epochs. These fossils have been found in the northern hemisphere.
But the discovery of a second tropic bird in New Zealand – the oldest in the world – suggests they emerged on the southern ancient microcontinent of Zealandia.
The new fossils have been described in a paper published in Alcheringa: An Australasian Journal of Palaeontology.
It has been ascribed the scientific name, Clymenoptilon novaezealandicum, or Zealandian Tropicbird.
Zealandia is an almost entirely submerged chunk of continental crust in Oceania. It broke away from the ancient supercontinent Gondwanaland 83–79 million years ago. The main portion of Zealandia that is above sea level today is New Zealand.
Debate has raged between geologists as to whether the continental mass is most accurately described as a submerged continent, continental fragment or microcontinent.
In 2017, a team of New Zealand geologists made international headlines when they produced a paper claiming that the 4.9 million km2 mass ought to be considered Earth’s 8th true continent. But the dispute is far from settled.
What is known about the Zealandian Tropicbird, however, is that it had some distinct features.
Unique skull and pelvic traits suggest different feeding or foraging habits compared to living and other extinct tropicbirds. But, because the legs of the specimen were not fossilised, more information about how it lived is tantalisingly elusive.
The presence of two tropicbirds and multiple species of early penguin from the beginning of the Palaeocene at Waipara Greensand suggest these ancient shores were a hub of seabird diversification immediately following the mass extinction at the end of the Cretaceous which saw the end of the “Age of Dinosaurs.”