If you’ve ever had a fear of dinosaurs, you’ve probably wondered how easy it is for them to hear you. While you probably won’t be hiding from a raptor ever in your life, it’s interesting to think about just how well they could hear their prey.
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Understanding the hearing of dinosaurs is complicated. When it comes to hearing, there are a lot of internal and external things happening all in a matter of seconds. All we have of dinosaurs are their skeletons, so we unfortunately won’t ever have an exact answer to this question.
However, there are definitely things that we can look at to get an educated guess. One of the most important things we can do—and something that researches do all of the time already—is compare animals that we already know to dinosaurs. By comparing the anatomy of these animals, we can figure out how well dinosaurs might have been able to hear. Most of this comparison is going to come from skull structure, but that skull structure does have a purpose.
How Do We Hear?
To actually understand why things like skull structure and comparisons matter, we have to have a general understanding of how hearing works. Hearing is a physiological process that all animals experience in some way and in most cases, it is very similar across the board. To make things simple, though, we will start with the physiological processes behind human hearing.
In humans, hearing starts at the outer ear. Our outer ears are a cone shape, made specifically to direct sound into the ear canal. At the end of that canal is the eardrum, which starts the middle ear.
Sound waves hit the eardrum, which moves tiny bones on the other side called ossicles. These bones move to the vibrations of the sound waves against what is commonly called the oval window but is medically named the fenestra ovalis.
The oval window is a membrane that connects those bones to the cochlea or inner ear. Through that membrane, the vibrations from the ossicles create waves in the cochlear fluid. The movement in the fluid is sensed by hair cells in the cochlea that send messages to the brain. These are the basic physiological processes behind hearing for humans and, in general, most animals.
Almost every animal has the ability to hear, but the strength of that ability depends on a few key factors. If the animal has an outer ear, the size and shape of it determine how much sound information is being funneled into the inner ear. If they do not have an outer ear, however, the size of the ear canal and eardrum are what determined the amount of information gotten.
What This Means:
There is one massively important fact about hearing that this involves this physiology. The bigger the eardrum, the lower the frequencies heard. The smaller the eardrum and ossicles, the higher. This is because heavier eardrums and bones are not going to be able to move fast enough to send messages to the brain about high-frequency sounds. If the bones and drum are light, they can move at a higher speed. These are what qualify any organism as having good or bad hearing.
If we are attempting to hypothesize about the hearing of dinosaurs, a long-extinct species, we must look at the hearing of their modern descendants. First, we can take a look at reptile hearing.
Reptiles do not have what we would think are outer ears. Instead, they have holes in the skull covered by a membrane called the tympanum.
These holes are usually found on either side of the skull where you would think outer ears should be. These holes lead directly into their ear canal. Reptile hearing usually depends on the individual animal. For the most part, reptiles have pretty standard hearing.
Turtles and snakes, however, have notoriously bad hearing for animals. While turtles do actually have outer ears, snakes have no outer ears at all. Their inner ears are very sensitive to ground vibrations (called subsonic sounds), moving the fluid in their inner ears. Turtles can also sense subsonic sounds, though not as well due to their additional outer ears.
Arguably the closes reptilian descendant of the dinosaurs is the alligator. Alligators ears are very similar to other reptiles, but instead of sitting on the sides of the face by the eyes they are placed on the top of the head. These holes are referred to as the upper temporal fenestra. Alligators and crocodiles are known for having good hearing on both land and in water.
The much closer descendant of dinosaurs are birds, which have an equally variant range of hearing between each of them. Unlike reptiles, birds’ outer ear does involve a small funnel shape with no membrane between it and the ear canal. If you are wondering if you just forgot what bird ears look like, don’t worry. Birds’ ears are covered by a layer of feathers called auricular that protect them from damage.
Most birds have a lower frequency range than humans, so they’re not particularly great at it. This is not true, however, for owls who are some of the best hearing terrestrial animals.
While birds do have a great hearing range, the frequencies that they do pick up are heard very precisely. Some birds, like the pigeon, can even hear frequencies so low that they can tell when storms are on their way.
So, while we can quantify hearing by the range of frequencies that are heard, there are many different ways to be good at hearing.
Evidence for Dinosaur Hearing
Now that we understand how some of the dinosaurs’ descendants can hear things, we can start to look at how they are similar and why certain dinosaurs might be better or worse.
When it comes to the anatomy that we need to compare, we obviously need to look no further than the skull. We’ll use three of the most popular dinosaurs—T. Rex, V. Raptor, and Brachiosaurus—as examples of dinosaur skulls.
As you will see when comparing all of these skulls, even with their vast differences, they all include at least two fenestrae on the skull. As you might remember, in human ear anatomy that oval window that begins the inner ear is called the fenestra ovalis. Fenestra, essentially, means small hole.
It is a word used to recognize any holes in the skull of dinosaurs that have not been identified as serving a specific physiological purpose. They can be assumed, however, to do so. Especially depending on the placement.
On all of the dinosaurs used as examples, one of the fenestrae is located in an area that is reminiscent of either bird or reptile ear anatomy. In the T. Rex, there are two fenestrae: a larger one behind the eye and a smaller one on the top of the head.
Due to the average size of the fenestrae on the modern animals that were discussed, the smaller holes seem more accurate. Though, there is something very interesting about the larger fenestrae.
At the top of the larger fenestra is a bone formation that caves into a smaller area. This formation in the skull suggests that the ear did, in fact, begin behind the eye instead of on top of the head for most terrestrial dinosaurs.
This formation can be seen most prominently in the lateral fenestra of the brachiosaurs. The forms of these fenestrae are also reminiscent of the human ear shape, strengthening the theory for it being the hole in which sound is sent to the ear canal.
If we are to go off of the assumption that this is the entry to the ear canal for dinosaurs, by the shape of it we might assume that instead of the outer membrane of the reptile, the dinosaur had a visible outer ear.
This outer ear could mean that dinosaurs have a similar hearing to larger birds, like owls. There is an equally good chance that dinosaurs might have a lower range but a great reaction time and understanding of sounds like pigeons.
What We Know
The best assumption that we might decide on, though, is that hearing was just as vastly different between each individual dinosaur as it is between individual animals today. Overall, experts believe that dinosaurs probably had exceptional low-frequency hearing.
This means that they were probably more pigeon than owl, but it’s important to note that this is all just theory. Unfortunately, we will probably never know how any dinosaur’s hearing was for sure due to a lack of middle or inner ear to look at. Based off of what we think, though, you can rest easy knowing that velociraptors probably didn’t have supersonic hearing.