1. Can Sound Reach Whales and Dolphins If Their Ear Holes Are Closed?
The deeper you go in the sea, the darker it becomes. For animals living there, sound is a clue that replaces sight. Sound travels far in dark places and curves around objects [2]. Also, sound moves faster in water than in air. It is said to be about 1500–1530 m/s (approx. 4920–5020 ft/s) in water and about 340 m/s (approx. 1115 ft/s) in air [1]. If you calculate 1530 divided by 340, the result is about 4.5 times faster. Some materials round this to "5 times," but the calculation shows it is roughly four and a half times.
However, whale species have sealed ear holes. Sound reaching their faces must travel through skin to reach the inner ear [3]. The material for this path is "acoustic fat" packed in the head. Fat transmits sound easily, and acoustic fat in the head helps conduct sound [1]. Also, whales do not have functional ear flaps. It is explained that fat gathers underwater sound instead of an ear flap and guides it to the middle ear [1]. So, which part of a dolphin’s face acts as the "ear"?
2. How Dolphins and Toothed Whales Receive Sound Through the Lower Jaw
In dolphins and toothed whales, it is thought that sound enters through thin parts of bone at the back of the lower jaw. This part is called the "acoustic window." Sound passes from the acoustic window through fat bodies in the lower jaw to the bones of the middle ear [4]. A researcher named Norris proposed this path in 1964, and it remains a leading explanation today [4]. However, we cannot say for sure that it is "only" the lower jaw. The same paper reports the possibility of another entrance closer to the throat [4].
Dolphins emit click sounds and project them as a narrow beam forward. Sound bouncing off prey is caught at the acoustic window in the lower jaw, passes through the middle ear, and goes to the brain [5]. Here, we focus on receiving the returning sound, not the side that produces it. Even if a house’s front door is closed, people can enter through a window. A dolphin’s lower jaw is like a window for sound entering. But this is just a simple analogy; in reality, it is a more complex structure combining bone, fat, and the middle ear. Where did these fat bodies come from?
3. Is the Fat in a Dolphin's Lower Jaw Left Over from Chewing Muscle?
Research from Hokkaido University provides clues about the origin of this fat body. It was found that acoustic fat in dolphins (the melon on the head and the lower jaw) shows gene activity that is intermediate between muscle and fat [3]. The research suggests that some chewing muscles, which became unnecessary as whales started swallowing prey whole, changed into fat bodies that transmit sound [3].
Tissue that lost its function as muscle may have taken on a new role. However, this is a view derived from how genes work; it cannot be said to be proven evolutionary fact. If the lower jaw is useful for small toothed whales, is it the same for baleen whales with much larger bodies?
4. How Baleen Whales Hear Low Sounds with Their Skull Bones
In 2015, researchers from UC San Diego and other institutions performed a 3D simulation of the head of a sei whale. For baleen whales, vibration of skull bones (bone conduction) is thought to be the main way they hear. In the simulation, for low sounds between 10–130 Hz, bone conduction was up to 10 times more sensitive than paths through soft tissue [6]. This was a result on a computer, not a measurement of living whales. The "up to 10 times" figure is also the upper limit within that low-frequency range.
In 2025, vibration experiments using the skull of a gray whale were reported. When underwater vibrations of 170–1000 Hz were applied, the bone on the middle ear side (tympanic bulla) moved more than the skull itself, showing that vibration was amplified in the specimen [7]. This supports the path where low sounds travel from the skull to the inner ear, but it was an experiment on a specimen, not a hearing test of a live whale.
The shape and number of turns in the cochlea spiral inside the inner ear are strongly related to the range of audible pitch. A study analyzing 41 specimens, including fossils, estimated that the ability to hear ultra-low sounds at or below 50 Hz was present by the mid-Miocene (about 23–5 million years ago), and the ability to hear below 20 Hz by the late Miocene [8]. How many Hz baleen whales can actually hear is not clear because there are few measurements of living individuals.
5. Do Seals' Ears Fill With Blood When They Dive?
Seals hear sounds in both water and air. A study reported in July 2026 states that sponge-like tissue in the middle ear of seals fills with blood when they dive, swelling to help transmit underwater sound to the eardrum. When they return to land, the blood drains away, and the structure returns to being filled with air [9].
This study analyzed over 200 living and fossil specimens using micro-CT scans. It states that this mechanism developed before about 26.7 million years ago. Some reports say about 26 million years ago, so it is safe to read this as a range of about 26–27 million years ago. The content introduced here is based on news reports [9].
Even within the same group, ear usage differs by species. Sea lions are types that hear well in air. Harbor seals hear almost equally well in air and water. Elephant seals are specialized for underwater hearing, so their sensitivity in air is sacrificed [10]. Fat, bone, blood—marine mammals used different materials as part of their "ears."
6. How to Look for Ear Holes on Marine Animals in Books and Aquariums
What you can do today: Line up photos of whale, dolphin, seal, and sea lion faces from books or photo collections. Try to find the "ear hole" and "ear flap." It is hard to see prominent ear holes or flaps on whales. Comparing this with the faces of seals and sea lions is good practice.
Also, try calculating 1530 divided by 340 on a calculator. This shows how many times faster sound travels in water than in air. It is sometimes rounded to "5 times," but dividing it yourself gives you 4.5.
What you can do when you go out: If you see dolphins, sea lions, or seals at an aquarium, compare where on their faces looks like an ear. When approaching the glass, observe quietly and follow the rules.
The question for next time: This article did not cover the story that "low sounds travel farther." Investigating why whale songs reach far away will reveal more about how sound travels in water.