Ancient Whales Could Hear Like Hippos And Camels, Fossils Show

Grapical Abstract:
Mourlam and Orliac describe the inner ear of two partly terrestrial early whales (Protocetidae). Comparisons with other fossil and modern whales and terrestrial relatives reveal that earliest whales’ hearing capacities were similar to those of their terrestrial kin and that infrasonic/ultrasonic hearing evolved after the emergence of modern whales. (Credit: Current Biology (2017) /
doi:10.1016/j.cub.2017.04.061)
The humpback whale (Megaptera novaeangliae) is a species of baleen whale. Baleen whales rely on infrasonic sounds.
(Credit: U.S. National Oceanic and Atmospheric Administration (NOAA) / Public domain)
A mother sperm whale and her calf off the coast of Mauritius. Sperm whales are toothed whales, which hear in the ultrasonic range.
(Credit: Gabriel Barathieu / CC BY-SA 2.0)

The structure of the cochlea, the headquarters of hearing in the ear, is described for two ancient protocetid whales

Field site in Kpogame, Togo, where the early whale ear bone fossils were unearthed. (Credit: L. Hautier 2016 / doi:10.1016/j.cub.2017.04.061)
Figure 1. Digital Endocasts of the Bony Labyrinth of Protocetid Specimens from Kpogame, Togo, with Highlighted Cochlea (A–C) ?Carolinacetus sp. UM-KPG-M164.
(D–F) Protocetidae indet. UM-KPG-M73.
(A and D) In situ cochlea through a translucent rendering of the petrosal bone presented in ventral view.
(B, C, E, and F) Detail of the cochlea in medial (B and E), ventral ©, and antero-ventral (F) views. Abbreviations: ca, cochlear aqueduct; cc, cochlear canal; fc, fenestra cochleae; fv, fenestra vestibuli; pb, petrosal bone; sbl, secondary bony lamina (imprint of basal ridge).

Early amphibious whales had hearing capacities close to those of their terrestrial kin

Figure 2. PCA of Nine Parameters of the Cochlea within Artiodactyla
This dataset was compiled based on the PCA of Churchill et al. [
ref], augmented by the two protocetids from Kpogame, ten land artiodactyls, and data from the literature [ref]. Red stars represent the protocetids; red circles represent the other archaeocetes. Triangles represent extant (orange) and Paleogene (yellow) land artiodactyls. Squares represent Oligocene (cyan), Miocene (light blue), and more recent (black) mysticetes. Crosses represent Oligocene (pink), Miocene (magenta), and more recent (purple) odontocetes. The large symbols correspond to the centroid of the three main morphospaces. Abbreviations: IF, infrasonic frequencies; MF, midfrequencies; UF, ultrasonic frequencies.

Extreme hearing abilities in whales derive from a mid-frequency ancestral ear

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𝐆𝐫𝐫𝐥𝐒𝐜𝐢𝐞𝐧𝐭𝐢𝐬𝐭, scientist & writer

𝐆𝐫𝐫𝐥𝐒𝐜𝐢𝐞𝐧𝐭𝐢𝐬𝐭, scientist & writer

PhD evolutionary ecology/ornithology. Psittacophile. scicomm Forbes, previously Guardian. always Ravenclaw. discarded scientist & writer, now an angry house elf