Baleen whales have sung basso profundo for 34 million years
Surprisingly, the blue whale’s deep voice was around long before its huge body.
Baleen whales produce and hear the lowest frequency sounds of any animal alive. Among evolutionary biologists it was generally assumed that such extreme acoustic ability was an adaptation linked to huge body size.
In a surprising finding, Australianled research published in Proceedings of the Royal Society B suggests the trait was around long before whales grew big.
Travis Park from Monash University in Melbourne set out to test the hypothesis that the big sounds of baleen whales had co-evolved with their size by investigating the fossilised earbones of their more diminutive ancestors – dolphin-sized toothed whales.
His team focused on fossils from 34 million years ago, the period during which filter feeders emerged as a distinct evolutionary line. Three-dimensional models were made of the whales’ cochleae – the spiral, hollow, conical bone chambers in the ear that facilitate hearing. The precise architecture of the structures allowed Park’s team to calculate the frequency ranges the whales could detect, and compare them with those heard by modern species.
The results showed striking similarities. The cochleae of the whales, big and small, ancient and modern, were adapted to very similar ranges. This suggests that low-frequency hearing is not an emergent property of increased mass but a pre-existing ability.
The finding is controversial, contradicting earlier research.
Park’s paper concludes that lowfrequency hearing is of very ancient origin, emerging long before the high-frequency sensitivities and echolocation abilities associated with toothed cetaceans such as sperm whales, narwhals and porpoises.
“The similarities of baleen whale cochleae to older whales shows us that this ability evolved well before other extreme adaptations such as baleen, filter feeding and gigantic body size,” says Park.
PARK’S PAPER SUGGESTS THAT, CONTRARY TO CURRENT ORTHODOXY, LOW- FREQUENCY HEARING IN WHALES IS OF VERY ANCIENT ORIGIN.