Evolution: whale and dolphin echolocation (Evolution)

by David Turell , Monday, November 20, 2023, 23:27 (158 days ago) @ David Turell

Discussing its history:

https://phys.org/news/2023-11-reveals-clues-whales-dolphins-echolocation.html

"A study published in Diversity provides new insight into how toothed whales and dolphins came to navigate the underwater world using sound waves.

"Whales and dolphins, which lack external ears, rely on a technique called echolocation to navigate and hunt in the dark. Much like shouting and listening for echoes, these animals emit high-pitched sounds that bounce off objects and reflect back at them, allowing them to map out their surroundings.

"Their skulls and soft tissues near and within the blowhole are asymmetrical, meaning that a structure on one side is larger or differently shaped than its counterpart on the other side. This "lopsidedness" enables the production of sound. At the same time, a fat-filled lower jawbone conducts sound waves to the internal ear, allowing the animals to locate where sounds are coming from (directional hearing).

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"Xenorophus was a large creature approximately three meters long that swam the waters of Eastern North America 25–30 million years ago and likely fed on fish, sharks, sea turtles, and small marine mammals. Externally, it resembled modern dolphins but had several interlocking molar-like teeth, much like an ancestral land mammal.

"Similar to today's odontocetes, Xenorophus had asymmetry around the blowhole, though not as pronounced as its living relatives. Notably, it also had a distinct twisting and shifting of the snout several degrees to the left. Previous studies in other ancient whales (archaeocete whales) suggest that this "snout bend" may be linked to the asymmetrical placement of fat bodies in the jaw, increasing directional hearing abilities.

"However, Xenorophus took this one step further. The fat bodies in its lower jaws, which functioned like external ears in land mammals, were tilted, further exaggerating directional hearing. This bending of the snout and tilting of the fat bodies may have been similar to the asymmetrical ears of owls, which can detect the precise location of prey based on their sounds.

"The new evidence suggests that Xenorophus, with lesser pronounced asymmetry near the blowhole, may not have been as adept at producing high-pitched sounds or hearing high frequencies as living odontocetes. However, it was able to determine the location of sounds. Therefore, Xenorophus likely marked a key transition in the history of how whales and dolphins came to use echolocation.

"'While this asymmetry is seen in other ancient whales, Xenorophus displays the strongest of any whale, dolphin, or porpoise, living or extinct," said Boessenecker. "In addition, although the blowhole-focused asymmetry in today's odontocetes can be traced back to Xenorophus and other relatives, the twisting and shifting of the snout is no longer seen today. This suggests that Xenorophus is a crucial puzzle piece in understanding how whales and dolphins evolved their echolocation abilities."

"In addition, while many scientists focus on symmetry in nature, Geisler says their new study demonstrates the importance of also examining asymmetry."

Comment: humans are symmetrical, but our eyes and ears have 3-D interpretation due to being apart. Bats use echolocation as we do with our ears, but dolphins have developed an asshmetical way of doing it