Ancient Sharks Feasted on Fatty Sperm Whale Noses 5 Million Years Ago

Shark ancestors have been found to have preferred to feed on the noses of ancient sperm whales thanks to their large fat content, according to research published in the journal Proceedings of the Royal Society B.

Sperm whales have large, fatty nasal organs, which they use to produce sounds like calls and sonar signals for echolocation. The authors of this paper report that they have analyzed the bite marks on several fossilized sperm whale skulls from the Miocene era, aged between 6 and 6 million years old, from the Pisco formation in Peru.

Bite marks consistent with the jaws of ancient shark species were found on the regions of the sperm whale skulls adjacent to these fatty nasal organs, mostly on the upper jaw bones, and the region around the eye. This indicates a feeding preference by sharks for this area of the whale's body.

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Artwork of a sperm whale carcass being scavenged. © Jaime Bran

"The noses of modern sperm whales have one of the highest concentrations of fats and oils available in nature, which are part of their nasal complex," Aldo Benites-Palomino, lead author of the study and PhD candidate at the University of Zurich, told Newsweek.

While the fossilized sperm whale skulls didn't contain any soft tissue, as fats don't tend to survive millions of years of preservation, the researchers inferred from the overall shape of the skulls that ancient sperm whales also possessed these fatty deposits, making for a perfect meal for sharks.

"Because during the late Miocene baleen whales were slender and smaller, these would have not constituted an ideal fat repository," said Benites-Palomino. "On the other hand sperm whales were a hyperdiverse group with at least seven species known so far from the Pisco region. These animals would have constituted an ideal food source."

In modern seas, sharks are noted to also prefer eating areas containing high concentrations of fats, like the blubber on the bellies of dead whales of all species. This study indicates that this preference has lasted millions of years, and that the sharks figured out that the fattiest part of a sperm whale, much more common back then, was the nasal region.

"As any large predator, sharks can also be opportunistic animals," said Palomino. "This behavior is what we see nowadays with whale carcasses as sharks prefer to scavenge specific regions. If the food is available these animals will prefer to scavenge."

The sharks didn't hunt the sperm whales for their fatty noses, rather scavenged the carcasses of dead whales. This was done before the whale sank to the bottom of the water column in a process known as a "whale fall," with the sharks feeding on the body as it floated.

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Lead author Aldo Benites-Palomino with one of the ancient sperm whale skull parts. © Aldo Benites Palomino

"Our findings indicate that all of these were post-mortem events. The carcasses were floating for days until all the fat was ingested by sharks, not being able to float any more."

According to the paper, the bite marks corresponded to several species of sharks feeding on the nasal region one after another: the overall shape, size and arrangement of the bite marks varied enormously. The most common shark species near Peru during this time period included mako sharks, great white sharks, sand sharks and the giant megalodon.

Several species of shark are involved in the first stages of scavenging dead whales in modern times, with pelagic species like reef sharks and white sharks feeding as the whale carcass floats, followed by benthic species like sleeper sharks after it has fallen to the seafloor.