Maybe we are stretching it a bit, but Dinosaurs were all over the world at one time. So this week at Hearing International we ask the question, What did the Dinosaurs hear? Did they hear anything? Were they deaf? Did they hear the “big bang” coming? Judging from movies like Jurassic Park, one would get the impression that they had very sensitive hearing, but let’s look at what is known.
Dooling et al. (2007) say that we know very little about dinosaur behavior because our information about these magnificent creatures comes almost exclusively from skeletal fossil remains. Mammal-like reptiles were the dominant land vertebrates several hundred million years ago, but most of these creatures perished in the Permian-Triassic extinction event (around 250 million years ago).
Dooling et al. further state that the remaining Archosaurs (Greek for “ruling lizards”) are today represented by birds and crocodiles, but this group also included the dinosaurs, which became extinct about 65 million years ago. Fortunately, the inner ears of the various archosaurs (birds, crocodilians, and extinct dinosaurs) show a high degree of structural similarity. This enables Dooling and colleagues to make predictions about the function of the inner ear in extinct species based on relationships among similar variables in living birds, which are the closest surviving relatives of the dinosaurs.
There is considerable similarity in the anatomy of the labyrinth among all archosaurs in spite of large differences in scale. It is on the basis of this similarity that scientists draw conclusions about hearing in extinct dinosaurs. Science Daily (2007) states that researchers focused on the part of the inner ear called the basilar membrane to conjecture about dinosaur hearing. Small, lightweight species with a short basilar membrane – a bird, for instance – can hear higher frequencies than larger species with a longer basilar membrane – a dinosaur.
In the figure below, the solid line represents human hearing. The other species represented are the Great Tit (a small small songbird), dogs and, of course, the brachiosaurus. To the researchers, it was obvious that the range of best hearing is much lower in these big dinosaurs than in their living relatives. Dooling et al. (2007) present the thresholds for various mammals related to dinosaurs as a function of frequency. For humans a thick continuous line, dogs a dot dashed line as mammalian representatives, and the great tit presented by a dotted line representing a small songbird.
Based upon analysis of the other species, a representation of the hearing ranges for Brachiosaurus brancai is represented by the wide gray line. Dooling and colleagues explain that the dotted area extending from the high-frequency limb of the human audiogram toward lower frequencies (small arrows) indicates a progressive high-frequency hearing loss that is, to a variable degree, characteristic of the hearing of many elderly humans. These curves show that hearing in dogs (and many other mammals) extends to frequencies in the ultrasonic range above 20 kHz, much higher than in humans and archosaurs. The high-frequency limit in birds, such as the Great Tit, is below that of normal-hearing humans and large dinosaurs have an even more restricted range of high-frequency hearing (below 1.5 kHz), which is well below that of humans.
Although I would like to take credit for this one, Dooling et al. end their article with this statement:
“Because the modern world is very noisy, it is not uncommon for aging humans to experience a progressive high-frequency hearing loss. In jest, we sometimes irreverently refer to aging humans as ‘dinosaurs.’ Interestingly, as hearing in aged humans becomes more limited at high frequencies, it does in fact become more like that of the dinosaurs!!”