Fossil pushes back whale evolution
New Zealand find represents the oldest baleen whale ever discovered. Andrew Masterson reports.
The world’s oldest known baleen whale has been identified from a fossil found in New Zealand.
Baleen whales, which comprise the suborder Mysticeti, are all filter-feeders, sieving small organisms from water sucked in and expelled through a curtain of keratin bristles. The group contains a wide variety of species, including the right, humpback and blue whales.
Among biologists it is generally agreed that baleen whales evolved from toothed whales (the Odontoceti), although the estimation of when the two orders last shared a common ancestor varies.
A DNA analysis led by Michel Milinkovitch from Yale University, US, and published in the journal Nature in 1993 found that the last common ancestor may have lived as recently as 10 to 15 million years ago.
A more recent genetic study, published in the journal Royal Society Open Science in 2015, suggests the division occurred much earlier, at around 34 million years ago.
Now, research by palaeontologists Cheng-Hsiu Tsai and Ewan Fordyce from New Zealand’s University of Otago seems to support the older date.
In a paper, also in Royal Society Open Science, the pair announce the discovery of an entirely new genus and species, which they call Toipahautea waitaki. Using a variety of dating methods, including the identification of fossilised microfauna found next to the whale, they place it at 27.5 million years ago – making it the earliest known baleen whale ever found.
The distinction, it should be said, is a comparatively narrow one. The area in which the fossil was found, known as the Kokoamu Greensand in the Waitaki region of New Zealand’s south island, is a bit of hotspot for ancient whales.
The area has also offered up Whakakai waipata, dated to 27.3 million years ago, and Horopeta umarere, a relative newcomer at just 25.2 million years old.
Tsai and Fordyce infer T. waitaki sported baleen, based on its jaw shape and evidence that its mouth was well supplied with arterial blood.
As an early – possibly the earliest – representative of the order, they suggest the species may have been a generalist and opportunist feeder – an intermediate form between fully carnivorous toothed whales and the full-time filter feeders that were its descendants.