Low-frequency hearing preceded the evolution of giant body size and filter feeding in baleen whales.
Living baleen whales (mysticetes) produce and hear the lowest-frequency (infrasonic) sounds among mammals. There is currently debate over whether the ancestor of crown cetaceans (Neoceti) was able to detect low frequencies. However, the lack of information on the most archaic fossil mysticetes has prevented us from determining the earliest evolution of their extreme acoustic biology. Here, we report the first anatomical analyses and frequency range estimation of the inner ear in Oligocene (34-23 Ma) fossils of archaic toothed mysticetes from Australia and the USA. The cochlear anatomy of these small fossil mysticetes resembles basilosaurid archaeocetes, but is also similar to that of today's baleen whales, indicating that even the earliest mysticetes detected low-frequency sounds, and lacked ultrasonic hearing and echolocation. This suggests that, in contrast to recent research, the plesiomorphic hearing condition for Neoceti was low frequency, which was retained by toothed mysticetes, and the high-frequency hearing of odontocetes is derived. Therefore, the low-frequency hearing of baleen whales has remained relatively unchanged over the last approximately 34 Myr, being present before the evolution of other signature mysticete traits, including filter feeding, baleen and giant body size.
School of Biological Sciences, Monash University, Melbourne, Australia travis.park@monash.edu.|Geosciences, Museums Victoria, Melbourne, Australia.
Travis
0000-0002-9492-8859
T
Park
School of Biological Sciences, Monash University, Melbourne, Australia.|Geosciences, Museums Victoria, Melbourne, Australia.
Alistair R
AR
Evans
School of Earth Sciences, University of Melbourne, Melbourne, Australia.
Stephen J
0000-0002-5593-2740
SJ
Gallagher
Geosciences, Museums Victoria, Melbourne, Australia.|Department of Vertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.|Department of Life Sciences, Natural History Museum, London, UK.
Erich M G
EM
Fitzgerald
D000818:Animals; D001315:Australia; D005075:Biological Evolution; D049628:Body Size; D005247:Feeding Behavior; D005580:Fossils; D006309:Hearing; D014907:Whales
Cetacea; Mysticeti; Oligocene; cochlea; evolution; fossil