LIVING MECHANISM
RECORD + HYPOTHESIS26.7 MYA–2026 · AMPHIBIOUS HEARING
Blood-filled tissue in a seal’s ear may carry sound underwater
A micro-CT comparison of more than 200 living and fossil specimens suggests that tissue protecting the ear from pressure also helps move underwater sound toward the cochlea.
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The case and the claim, up front
- What was observed
Researchers report that cavernous tissue around the middle ear swells with blood during a dive, helping protect the ear from pressure changes.
- Which way the result moved
The study compares anatomy and evolutionary history; it did not directly measure blood flow and hearing performance in every living seal at every depth.
- What remains unproved
Anatomical and evolutionary comparisons do not directly measure hearing at every frequency and depth across all species.
The record
A study described by London’s Natural History Museum compared more than 200 living and fossil pinniped specimens using micro-CT scans. Researchers report that cavernous tissue around the middle ear swells with blood during a dive, helping protect the ear from pressure changes.
Because blood has a density similar to seawater, the researchers argue, most underwater sound can pass through the middle ear toward the cochlea. About 40 percent of the specimens were scanned at the museum’s Imaging and Analysis Centre.
The fossils suggest that this amphibious hearing mechanism evolved at least 26.7 million years ago. The study compares anatomy and evolutionary history; it did not directly measure blood flow and hearing performance in every living seal at every depth.
The turn
Underwater hearing may not be only a problem of sealing the ear away from its environment. To cross the boundary, part of the body may need to take on physical properties closer to the water around it.
Three possibilities
First possibility. The tissue that protects against pressure may also serve as a route for sound.
Second possibility. A seal’s ear may behave less like one fixed sensor than a transformer changing state between land and sea.
Third possibility. Sensation may sometimes depend not on receiving the outside more intensely, but on briefly becoming more like it.
The editorial conclusion
A seal does not open its ear wider to hear the sea. It dives carrying a small sea made of blood around the ear.
The case against it
Anatomical and evolutionary comparisons do not directly measure hearing at every frequency and depth across all species. They also provide no basis for human hearing treatments or diving-safety advice.
What the record cannot tell us
How do blood volume and sound transmission change together during a real dive? Direct measurements are also needed to show how this structure responds as ocean noise increases.
Corrections
There are no public corrections at this time.
Translation and reporting Mara Venn / Fact-checking Gideon Park / Implications Imani Sloane / Boundaries Ruth Alder / Copy Jonah Reed / Reader review Mae Bell / Production Theo March / Publisher Ada Mercer