Dinosaur Communication and Vocalization

A Diagram of a juvenile and sub-adult Corythosaurus' nasal crests.

 These passageways in the crest most likely helped the dinosaur with communicating.

Communication in dinosaurs has always been a troublesome concept to understand. Why? Well, nobody's heard a dinosaur in more than 65 million years! All kidding aside, nobody knows what a dinosaur sounded like and sounds don't get fossilized. However, some discoveries and papers were presented recently, and have finally given us a some good clues as to what dinosaurs sounded like. These findings have been very important since knowing what dinosaurs sounded like can give us some good clues about their behavior and tell us what they were like when they were alive.
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The Mesozoic Music of Parasaurolophus

One of the first major finds when it came to dinosaur communication came in 2007. Scientists from the Sandia National Laboratories and the New Mexico Museum of Natural History collaborated together to find out the exact noises and calls of a well recognized dinosaur, Parasaurolophus.

Parasaurolophus was a large herbivorous dinosaur that lived 75 million years ago. It was a member of the Lambeosaurids, a group of duck-billed dinosaurs that thrived at the end of the age of dinosaurs. It's most distinguisable by a elongated crest sticking out of the back of its skull, forming a banana-like structure attached to its nasal passageways. For a long time this crest was thought to be used as a snorkel while foraging underwater, since it was widely thought that these animals were water dwellers. However, the study showed otherwise.

The study used advanced computer tomography and C-T scans on a well preserved 4.5 foot long Parasaurolophus skull. They found that unlike originally thought, Parasaurolophus didn't have an opening on the top of its crest through which it could breathe. Instead, the study found that the skull was filled with complicated tubes and chambers, which showed a striking resemblance to a trombone.

After the C-T scans were made, the computer then made a digital copy of the skull and simulated air flow in a type of 3-D virtual instrument. Variations were then made to accommodate the lack of vocal chords, as it was unknown whether or not Parasaurolophus had them. I'll talk more about this later in the post.

These calls were within the low frequency range -- so low that much of the actual sound isn't picked up in our ears. However, studies of  Parasaurolophus' brain case have shown that it was capable of hearing very low frequencies. This means that Parasaurolophus was using its calls to communicate with others of its species, suggesting that it was possibly a social animal and used its advanced nasal tubes for communicating complex messages with other Parasaurolophus. Thus, this discovery gave us a very good idea as to its behavior and how it lived.

A recreation of Parasaurolophus' odd voice

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The Noses of Armored Behemoths

In the following years, scientists continued to make more and more finds about the sounds dinosaurs made. Many were completely unexpected and downright bizarre. One of them was in 2008 when scientists at Ohio University discovered something in two armored dinosaurs:  Euoplocephalus and Panoplosaurus.

A Euoplocephalus Skull
Note the complicated nasal passages.

Euoplocephaulus (Skull is Pictured right) was an ankylosaurid dinosaur that lived about 72 million years ago. It was a heavily armored quadrupedal herbivore with a thick club at the end of its tail. Euoplocephaulus is probably most famous for the fact that it has a mix of thick armor, spikes, a powerful tail club, and most surprisingly, armored eyelids, making it one of the most well protected animals ever to have lived. Euoplocephaulus is arguably one of the most well documented ankylosaur.  We've got a large number of  partial and complete skulls and skeletons of it and almost every piece of its anatomy is known.

Panoplosaurus lived in the same time and place as Euoplocephaulus, but it didn't seem to be as heavily armored. It was a member of the nodosaurids, close relatives of the Ankylosaurids which have longer tails, legs, and skulls than the ankylosaurids, but don't have as thick armor or the clubed tail. However, unlike Euoplocephaulus, it has long spikes on its shoulders that could also have been useful for defense, and the skull from the only known specimen also shows that it had thick armor plating over its cheeks as well.

The study was started to try and map the complex airways and channels within multiple dinosaurs' skulls and brain cases, from nasal channels to air sacs. However, while examining these two dinosaurs, they found something unexpected. According to the C-T scans, Euoplocehalus' and Panoplosaurus' nasal passages took a long, twisting, looping course through the snout from the nostril all the way to the back of the throat. It was already known that the nasal passageways were well developed and elongated, as it was thought smell was one of their primary senses, but these complex looping chambers were completely unknown.

Since there was an area with large blood vessels surrounding the passageways, the scientists thought it might have something to do with heat exchange. This structure could warm up air that comes into the body, and thus warm up the animal. But more examinations showed these passageways were also oddly similar to Parasaurolophus' nasal chambers, and thus could have also been used as a method of communication.

As the study progressed, they mapped both animals' brain cases and found that the inner ear was fine- tuned to hear low frequencies. This was the same pattern as seen in Parasaurolophus -- long complex nasal chambers and good low frequency hearing -- suggesting again that these dinosaurs used their nasal chambers for communicating.

Euoplocephalus and Panoplosaurus got almost no attention, despite being the most interesting part of the article. Even I didn't hear about the discovery until recently. I hope that this discovery will become more widespread and known in the future.
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What about Vocal Cords?

Mammals have vocal cords. Crocodiles have them as well, but what about dinosaurs? Many people might find this to be a silly question, but actually, most animal groups don't have vocalization structures. Only a select few types of animals are able to communicate vocally with a Larynx (the scientific term for vocal cords). Were dinosaurs able to as well? Let's see.

Modern day crocodilians, as I said before, have vocal cords. Dinosaurs' closest living reptilian relatives are crocodiles, so we should expect them to have it as well. However, it is impossible to find out exactly when the larynx in crocodilians appeared, as it shows no sign of itself on fossils. The latest a larynx could have appeared is during the early Cretaceous, when the ancestors of modern day crocodiles, alligators, and gharials first appeared, known as the Isisfordia. So crocs can't help us here, nor should they.

You see, crocodiles do have a larynx which they use to communicate vocally with low roars, but birds, the decedents of Dinosaurs, don't. Birds instead have a Syrinx (Pictured left), the avian version of vocal cords, which is located farther down near the base of the trachea, and is arguably more advanced. It is a structure that evolved completely independently from the larynx, so the ancestor of both birds and crocodiles, and the ancestor of the archosaurs, had no vocalization organ. Dinosaurs, being part of the bird side of the archosaur family and their immediate ancestors, would have likely had a syrinx instead.

However, their is a twist to this idea. The avian syrinx, unlike the Larynx, leaves evidence of its presence on animal bones, and should be seen in dinosaur anatomy. A major factor for the syrinx in birds to operate is a structure called the clavicular air sac. Located in the chest cavity of birds, it is an organ that allows the syrinx to function, but when looking at Dinosaur anatomy, they seem to lack one. There is no evidence of a syrinx or a clavicular air sac in dinosaurs (with the exception of the Allosauroid Aerosteon, which likely evolved its clavicular air sac independently from birds and developed it for another purpose). The earliest signs of such a structure are seen in the primitive ornithothoracine birds, which means all dinosaurs likely couldn't vocalize. Therefore, noises such as grunts, bellows, chirps, shrieks, and roars were impossible for most dinosaurs.

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Sorry Dinosaur Fans, T-Rex Didn't Roar

The discovery that Dinosaurs lacked vocalization organs definitely will disappoint Dinosaur fans young and old alike, but this doesn't necessarily mean Dinosaurs were silent animals. Just look at modern day animals that lack vocal cords, such as Komodo Dragons. They are still very loud animals that communicate through deep hisses, tooth grinding, and jaw claps. There are also a few species of birds alive today that lack a syrinx, such as California Condors, which instead communicate through hisses and other non-vocal sounds.

Tyrannosaurs, and other large theropods with an increased surface area in their mouths, could create loud, booming claps with their jaws. Hisses could also have been a major way of communicating in carnivores, and the large sizes of the throat and esophagus could deepen these hisses. Smaller carnivores, like Dromeosaurids and Ornithomimids with an elongated trachea, could also change the pitch of their hisses. Swans use a similar method thanks to their elongated trachea structure.

An elongated Trachea is also present in the long necks of Sauropods, and also could deepen and control the pitch of hisses. Their have also been some theories that suggest the tails of Diplodocids could be used to produce noises, similar to how a whip cracks as it slices through air. Personally, I also think there is a possibility that some Stegosaurids could shake the plates on their back to create a sound display.

This discovery, however, doesn't mean the elongated nasal tubes in Lambeosaurids and Ankylosaurs were not capable of creating sound. Some species of snakes are capable of using chambers in the skull and nasal passageways to lower the frequency of hisses, meaning they could still use these chambers to produce noises.  Brachiosaurids also have large nasal chambers on the top of the skull. These chambers could be filled with air and used like Parasaurolophus' crest to amplify noises, somewhat like how a drum amplifies the vibrations around it. Hadrosaurs might have possessed nasal sacs that could do the same thing.

Dinosaurs could even use their environment to communicate.  Modern day animals splash in water, stomp on the ground, knock on trees, and beat their wings (which could be achieved by some feathered dinosaurs) to communicate. But it seems that Dinosaurs likely used other ways to communicate rather than just noises. Like most modern birds and reptiles, dinosaurs mostly used visual displays to communicate.

Most dinosaurs have visual structures on their bodies, such as crests, horns, frills, domes, plates, spikes, sails, and feathers, all of which could be used for visual communication. It seems dinosaurs used similar methods that both reptiles and birds use today, methods they use to distinguish themselves from related species, attract mates, frighten predators, and show their age. This is likely why such structures evolved in the first place, due to pressures to communicate as they became more advanced animals.

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Conclusions

Seems like dinosaurs couldn't roar like they are typically portrayed in popular culture and movies like Jurassic Park, but seem to have found many ways around that problem. Dinosaurs were definitely different in their approach to life than modern day large mammals, and we should expect such things. Dinosaurs aren't mammals, they're archosaurian reptiles, so we shouldn't expect them to act or behave like mammals. We should, however, expect them to behave like reptiles and birds, the animal groups that they actually belong to.

This is why I personally dislike calling Triceratops a "Mesozoic Rhino" or Velociraptor a "Cretaceous Wolf." I'll write a post about those theories in the future. Until then, please leave a comment so I know you're all listening and I'll do my best to answer.

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Link to Sources:

Parasaurolophus Nassal Passageways: http://www.sandia.gov/media/dinosaur.htm

Ankylosaur Nassal Passageways: http://witmerlab.wordpress.com/2011/09/29/an-armored-dinosaur-gets-a-second-opinion%E2%80%94and-the-crazy-straw-nasal-passage-survives/

Vocal Cords were Absent in Dinosaurs: http://www.tandfonline.com/doi/full/10.1080/08912960903033327