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In today's oceans, killer whales hunt other species of whales, working in packs to take down their much bigger prey. But living whales have it easy. Those that swam off the coast of Peru around 12 million years ago were hunted by a far bigger predator, a recently discovered animal with a very appropriate name: Leviathan.
Leviathan melvillei, named after the Biblical sea monster and the author of Moby Dick, was a giant sperm whale that has just been discovered by Belgian scientist Olivier Lambert. At between 13.5 and 18.5 metres in length, it was no bigger than the modern sperm whale, but it was clearly far more formidable.
Today's sperm whale has no functional teeth in its upper jaw and only small ones in its lower jaw (which are mostly used in fights). It feeds through suction, relying on a rush of water to carry its prey into its open mouth. But Leviathan's mouth was full of huge teeth, the largest of which were a foot long and around 4 inches wide. This was no suction feeder! Leviathan clearly grabbed its prey with a powerful bite, inflicting deep wounds and tearing off flesh as killer whales do, but with a skull three times bigger.
Leviathan was at the very top of the food chain and it must have needed a lot of food. While modern sperm whales mainly eat squid, Lambert thinks that Leviathan used its fearsome teeth to kill its own kind – the giant baleen whales. At the same point in prehistory, baleen whales started becoming much bigger and they were certainly the most common large animals in the area that Leviathan lived in. Lambert thinks that the giant predator evolved to take advantage of this rich source of energy. He says, "We think that medium-size baleen whales, rich in fat, would have been very convenient prey for Leviathan."
It's perhaps no coincidence that the biggest shark in history – the mighty Megalodon – also appeared at the same time in the same part of the world. It too was thought to have hunted whales and many of its teeth have also been found at Cerro Colorado. For the moment, it's hard to say if the two predators were direct competitors, since they may have swum in different parts of the Peruvian seas. Lambert speculates that the adults of either species could have eaten the young of the other but there's no evidence for this yet.
In the last few years, other smaller prehistoric sperm whales have been found in Peru and Italy. Their powerful teeth told us that these predators bit their prey in the manner of killer whales. The teeth were generally quite small but, as early as 1877, fossil hunters have found much larger teeth that looked very much like those of a sperm whale. The teeth provided tantalising hints of a much bigger animal but they were never accompanied by an actual skull. Their owner remained an enigma.
Lambert set out to find that skull in 2006, leading several expeditions into Peru's Pisco-Ica desert. The digs weren't fruitful but the team's luck took a turn for the amazing at the very end. "In November 2008, on the last day of the field trip, my Dutch colleague Klaas Post discovered a very large cetacean skull," says Lambert. "Usually large skulls belong to baleen whales, but Klaas immediately noted enormous teeth, both on the upper and lower jaw." They had found Leviathan.
The skull is beautifully adapted to capture large, powerful prey. The snout was short and wide, allowing it to bite more strongly with its front teeth and resist the struggles of its prey. Its temporal fossa – the shallow depression on the side of the skull – was enormous and could old huge jaw-closing muscles. The bite would have been the largest of any tetrapod (the animal group that includes mammals, birds, reptiles and amphibians). And the teeth were deeply embedded in the jaw bones for each support, and interlocked to give the animal a shearing, meat-carving bite. They were also angled forwards, giving Leviathan a better grip on prey with curved bodies.
The skull also creates a mystery. Sperm whales have a unique organ in their heads called the spermaceti, and Leviathan's was particularly large. The spermaceti is full of a waxy substance that was originally thought to be the animal's sperm (hence the name). Its purpose isn't clear although there are many theories, all of which must now be considered in the light of Leviathan's very different lifestyle.
The sperm whale might use it to control its buoyancy during a dive by pumping in cold water, solidifying the wax and increasing the density of its head. At the depths, the energy expended during a hunt heats up the wax and melts it again. But Leviathan probably didn't hunt for squid and probably wasn't a deep-diver like the modern sperm whale. In light of this, other explanations become more intriguing. The case containing the spermaceti could be used as a battering ram during fights. It could also boost the sperm whale's echolocation, allowing it to stun its prey with sound, or woo females (the male's organ is particularly big).
Reference: Nature http://dx.doi.org/10.1038/nature09067
More on ancient whales:
- Whales evolved from small aquatic hoofed ancestors
- Sperm whale poo offsets carbon by fertilising the oceans with iron
- Ever since there have been whales, there have been Osedax worms eating their bones
- Scientists, film-makers team up to expose illegal international trade in whale meat
- Echolocation in bats and whales based on same changes to same gene
- Fossil foetus shows that early whales gave birth on land
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