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‘White whale’ is a ghost of sperm whales’ past

Whales are pretty majestic creatures, in spite of their enormous size. Among living whales, the sperm whale is the largest of the toothed whales, and the largest toothed predator on Earth. It comes from a group known as Physeteridae, which includes just two other species: the dwarfed sperm whale, and pygmy sperm whale of the genus Kogia.

While the larger species of sperm whale is considered to have a vulnerable conservation status, both the pygmy and dwarf sperm are data deficient, which means that any information we can glean on this group could be super important for helping to protect them. Physeterids are considered to the most early branching group of the larger group of toothed whales, known as odontocetes. This also means that any fossils we can find of sperm whales can help us to understand the origins and early evolution of odontocetes.

Researchers have identified a new genus of ancient sperm whale based on re-examination of fossils known for over a century, and published in the open access journal PLOS ONE.

The fossils of the new whale date from an epoch known as the Miocene, around 14-16 million years ago. The remains, including a skull, jaws and teeth, were actually discovered in Santa Barbara County, California, in the 1880s, but their true identity and importance remained locked away until now.

Boersma with the partial whale skull fossil. Credit: A. Boersma
Lead author A. Boersma with the partial whale skull fossil. Image credit: Jame di Loreto, Smithsonian

The bones are bleached white, reflected in the new genus name, Albicetus, which translates in Latin to ‘white whale’, in honour of Herman Melville’s notorious leviathan, Moby Dick. “It only seemed appropriate to evoke Melville’s white sperm whale, Moby Dick, especially since we studied Albicetus oxymycterus alongside the skeletons of some of its modern day relatives in the collections here at the Smithsonian”, says Nick Pyenson, curator of marine mammals in the Department of Paleobiology at the Smithsonian, Washington DC, and co-author of the study. The jaws of Albicetus have been displaced through the ravages of times, providing the inspiration to connect the specimens to the famous literary monster, which was described as a creature of ‘unwonted magnitude’ with a ‘deformed lower jaw’.

Alexandra Boersma, lead author of the study, and an undergraduate student at Vassar College in New York, noticed that the fossils were unlike any known whale species while surveying the collections at the Smithsonian. They were originally described by Remington Kellogg in 1925, and as part of the genus Ontocetus, which is actually an invalid taxonomic name now with the original fossils actually represent a walrus tusk!

Despite their impressive size, and weight of more than 100kg, Boersma managed to construct a cool 3D model of the fossil specimens, which can be found (and played with!) here. Albicetus would have reached a maximum size of around 6 metres in length, much smaller than modern sperm whales which can reach over 20 metres in length. Species of Kogia are much smaller, in case you couldn’t tell from their names, coming in at only around 2.5-3.5 metres in maximum length. As the oldest member of Physeteridae, this implies that large body size in sperm whales evolved independently at least twice.

Larger whales usually tend to have larger teeth, which were probably for catching larger prey to sustain the increasing demands that come with being bigger bodied. Albicetus had very large teeth for its size, which indicates that it might preferentially have chowed down on other marine mammals like seals and smaller whales, differently from modern sperm whales which primarily dive deep to feed on squid, and actually don’t really use their teeth. “This find means that, around 15 million years ago when there were a lot of large sperm whales with big teeth like Albicetus, it may have been a moment of peak richness in the number and diversity of marine mammals serving as prey to these whales,” Boersma suggests.

A pod of Albicetus taking it easy out on the ocean. Image credit: A. Boersma
A pod of Albicetus taking it easy out on the ocean. Image credit: A. Boersma

The re-discovery of Albicetus, and new estimates of its size, have important ecological implications. During the middle of the Miocene epoch, this means that there were multiple, large and hypercarnivorous whales roaming the oceans, and often living alongside one another. Such communities simply do not exist in modern oceans, where hypercarnivory is relatively rare. This might have been due to the high diversity of marine mammals as prey items, but shows once again that we cannot use modern animals exclusively to reconstruct the history of different groups of animals – the fossil record is key!

The timing of this discovery couldn’t be any better, coinciding with the release date of Ron Howard’s new epic, ‘In the Heart of the Sea’, based on the story of Moby Dick and the sinking of the ship, Essex, by Nathaniel Philbrick in a novel of the same name. The film is set to hit screens in the US on December 11th.

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