What Do Sperm Whales Have To Do Late Miocene Sharks? A Lot, It Turns Out.

It’s a show-down as old as time: grand behemouth of a marine mammal versus ancient monster of a shark. These shark–cetacean trophic interactions span eons, preserved as bite marks in our fossil record to be discovered by researchers all around the world. Most of these fossils are isolated or fragmentary findings that bear limited information about major trophic patterns or roles of the past. In a new article, scientists provide evidence of focalized foraging by sharks in the form of tooth bite marks over physeteroids fossil bones from the late Miocene of Peru (from about 23 million to 2.5 million years ago).

Today, Peru is the third largest country in South America, after Brazil and Argentina. While thousands of visitors flock to here to cast their eyes on the Inca citadel of Machu Picchu, this sit is just a flash in the history of this country – or of its surroundings. The oceans back then, much like today, were teeming with life. From the smallest organisms to the largest of predators, physeteroid toothed whales were one heck of a foe to go up against. Yet, something definitely did, as their scattered remains have been uncovered in the Pisco Formation. A geologic formation located in the Ica Desert of southern coastal Peru, it is a globally significant fossil deposit known for its outstanding Cenozoic marine Fossil-Lagerstätten worldwide.

It wasn’t a surprise to see sperm whales (Physeteroidea) here. Physeteroids are among the oldest lineages of crown Cetacea, and while living sperm whales are represented by only three species (Physeter macrocephalus, Kogia breviceps and Kogia sima), their fossil record provides evidence of an ecologically diverse array of different forms. But what was surprising was the marks on the bones.

Bite marks.

This remnant of ancient life helps researchers today by providing direct evidence for trophic interactions and competition in the fossil record. These recently published findings indicate that sharks were targeting the forehead of these whales to actively feed on their lipid-rich nasal complexes. Sperm whales are well-known for their nose accounting for roughly a third of the animal’s total length and weight. One would think this would make for an amazing sense of smell, but all toothed whales lack an olfactory bulb. Instead, that head is filled with spermaceti, which has incredible resonating capabilities that allows for them to find prey by echolocation (a biological sonar used by several animals besides sperm whales). These predators are famous for diving into the deep to hunt for a meal by semding out high-frequency clicks that will then bounce off an object, returning an echo that provides a location of that object (aka the prey). It is essential for sperm whales in capturing prey; and makes them prey themselves. The sperm whale’s enlarged fatty forehead organs are a perfect target, as lipids are major sources of metabolic energy in sharks.

“The main organs of this complex are the spermaceti and the melon, structures rich in fats and oils, but also heavily regulated by the facial muscles,” explained study lead author Aldo Benites-Palomino, a paleontologist at the University of Zurich. “Most of the bite marks have been found on the bones that would be adjacent to these soft tissue structures, such as the jaws, or around the eye, thus indicating that sharks actively targeted this region.”

The bite marks varied, indicating multiple species of sharks took advantage of this feast. Some probably belonged to feared Megalodon, while others seem to coincide more with modern-sharks. But why did they go after sperm whales were baleen whales were also around during the Miocene? “During the Miocene baleen whales were small, but sperm whales would have constituted a perfect fat repository due to their greatly enlarged and lipid-rich nasal organs,” said Benites-Palomino. “Similar bite patterns can be recognized on other Miocene physeteroids fossils from across the globe, suggesting that sharks actively exploited physeteroid carcasses as fat sources.”