30-Million-Year-Old Fossils Shed Light on How Whales, Dolphins’ Echolocation Evolves

Dolphins and whales do not have ears and rely on their echolocation abilities to hunt and navigate. A new study has shed light on how this particular skill evolved.

Echolocation Evolution in Dolphins, Whales

In a new study, New York Institute of Technology's Professor Jonathan Geisler and Dr. Robert Boessenecker from the University of California Museum of Paleontology examined an extensive fossil collection that included two species of dolphins from the same genus Xenorophus - the Xenorophus sloanii and the newly-discovered species Xenorophus simplicidens.

All living echolocating whales and dolphins belong to the suborder Odontoceti, which includes some of these primitive species. Xenorophus dolphins were massive, 3-meter-long animals that lived in the waters of Eastern North America about 25-30 million years ago. They consumed fish, sharks, sea turtles, and small marine mammals for food.

They featured several interlocking molar-like teeth, much like an archaic terrestrial animal, but they looked like modern dolphins from the outside. Xenorophus shared an asymmetry surrounding the blowhole with modern odontocetes, but they were not as noticeable as its extant relatives. Moreover, their snouts were noticeably twisted and shifted several degrees to the left.

This "snout bend" may be related to the asymmetrical arrangement of fat bodies in the jaw, which improves directional hearing, according to earlier research on other ancient whales.

But Xenorophus went one step farther than that. Their slanted lower jaws, which served as their equivalent of land mammal external ears, amplified their directional hearing even more.

The asymmetrical ears of owls, which can pinpoint the exact location of prey based on their sounds, may have been comparable to the bending of the snout and tilting of the fat bodies.

The new data implies that Xenorophus would not have been as skilled at hearing high frequencies or making high-pitched sounds as modern odontocetes due to less obvious asymmetry at the blowhole.

Still, the researchers managed to pinpoint the exact locations of noises. Thus, Xenorophus most likely signified a significant turning point in whale and dolphin echolocation evolution.

Although other ancient whales exhibit this asymmetry, Dr. Boessenecker stated that Xenorophus exhibits the strongest of all whale, dolphin, and porpoise species, whether they are extinct or still alive. Furthermore, the twisting and shifting of the snout is no longer observed in modern odontocetes, even though the blowhole-focused asymmetry in these animals can be traced back to Xenorophus and their cousins.

"This suggests that Xenorophus is a crucial puzzle piece in understanding how whales and dolphins evolved their echolocation abilities," the expert concluded.

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What Are Cetaceans?

Cetacean refers to any member of the entire aquatic group of mammals known as whales, dolphins, and porpoises. They are considered mammals because they have hair, breathe air, give birth to live young, and produce milk. However, cetaceans were frequently categorized as fish because of how their bodies were built.

Meanwhile, manatees, dugongs, and Steller's sea cows are among the members of the order Sirenia. They were once known as the "herbivorous Cetacea." Nevertheless, cetaceans are exclusively carnivorous.