2011/08/22 by Julia M. Fahlke, Philip D. Gingerich, Robert C. Welsh +1 · 4 citations
Environmental Science · Earth and Planetary Sciences · Biochemistry, Genetics and Molecular Biology · #Marine animal studies overview #Underwater Acoustics Research #Animal Vocal Communication and Behavior
paper · pdf · doi:10.1073/pnas.1108927108
openalex publication_date 2011/08/22 · openalex created_date 2025/10/10 · openalex updated_date 2026/06/11
Eocene archaeocete whales gave rise to all modern toothed and baleen whales (Odontoceti and Mysticeti) during or near the Eocene-Oligocene transition. Odontocetes have asymmetrical skulls, with asymmetry linked to high-frequency sound production and echolocation. Mysticetes are generally assumed to have symmetrical skulls and lack high-frequency hearing. Here we show that protocetid and basilosaurid archaeocete skulls are distinctly and directionally asymmetrical. Archaeocete asymmetry involves curvature and axial torsion of the cranium, but no telescoping. Cranial asymmetry evolved in Eocene archaeocetes as part of a complex of traits linked to directional hearing (such as pan-bone thinning of the lower jaws, mandibular fat pads, and isolation of the ear region), probably enabling them to hear the higher sonic frequencies of sound-producing fish on which they preyed. Ultrasonic echolocation evolved in Oligocene odontocetes, enabling them to find silent prey. Asymmetry and much of the sonic-frequency range of directional hearing were lost in Oligocene mysticetes during the shift to low-frequency hearing and bulk-straining predation.