Evolution: Whales, dolphins and hoofed mammals?by Rebecca Priestley
Recent genetic evidence tells us the hippo is the closest living relative of whales and dolphins.
‘In palaeontology, we’re always dealing with extinction,” says Ewan Fordyce, professor of geology at the University of Otago. The species he studies – shark-toothed dolphins, giant penguins, ancient baleen whales – are all extinct, but there are clues to their evolution and extinction in the Waitaki marine sediments Fordyce has been studying for the past 30 years. “In the past couple of decades we have got some eye-opening evidence about the evolution of whales and dolphins,” says Fordyce. Genetic analysis has revealed they are very closely related to hoofed mammals – “perhaps the closest living relative of dolphins and whales would be the hippopotamus” – but there is still a lot to be learnt from fossils. “One of the really exciting advances in understanding whale origins was the discovery of whales with feet, and the feet included the basic double pulley bone, or knuckle bone, that typifies hoofed mammals,” he says.
The very earliest forms of whales and dolphins evolved about 55 million years ago and looked like a strange hoofed land mammal paddling in the sea. Modern whales and dolphins evolved about 35 million years ago. That evolutionary event is what Fordyce is really interested in. “I’ve been pursuing the link between the origins of modern whales and dolphins, the breaking apart of Gondwana, the opening of the Southern Ocean and changes in nutrient cycles in the sea that might have triggered the evolution of the two modern groups.” By looking at the sediments in which the fossils are found, palaeontologists can see what was happening in the oceans at the same time as these groups evolved or disappeared.
One of Fordyce’s students, Felix Marx, recently linked the diversification of baleen whales to big pulses of diatoms in the global oceans over the past 25 million years. “So that suggests a link between baleen whale evolution and ocean productivity,” says Fordyce. But many of those species have subsequently become extinct. Understanding why species evolve and then go extinct is the main driver of Fordyce’s work. He hopes that studying the fossil record will provide clues about what tips the balance and drives a species to extinction – these clues can be applied to today’s vulnerable and endangered species. “I feel quite strongly, when I look at the fossil record, that extinction is the norm,” says Fordyce. “Everything is going to go extinct. But today, extinction is a human problem – we’re doing it. If all these groups are already struggling like crazy to survive, then when humans come along that adds another dimension.”
BUT NOT FORGOTTEN
Five extinct New Zealand species it would be cool to still have around.
- The South Island giant moa (Dinornis robustus) was an enormous plant-eater with leg bones up to 1m long. The birds were hunted to extinction soon after the arrival of humans.
- With a wingspan up to 2.6m, the haast eagle (Harpagornis moorei) used its tiger-sized claws to crush moa and its long beak to reach into the carcass to feed. It went extinct once its moa prey disappeared.
- The kairuku, or giant penguin (Kairuku waitaki), was taller and heavier than an emperor penguin, though with its long wings, slender body and spearlike bill it was a very different shape. The kairuku lived in the Oligocene epoch around 28 million years ago.
- The shark-toothed dolphin (Waipatia maerewhenua) had a head like a modern dolphin and a mouth full of sharp teeth. Like the kairuku, this small mammal lived about 25 million years ago, when most of New Zealand was submerged.
- The mosasaur (Prognathodon overtoni) was a marine reptile that lived in the Cretaceous
period around 80 million years ago. These swimming lizards preyed on fi sh and squid and could crack the shells of turtles and ammonites with their strong teeth.
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