Dinosaur Dentition: The tribology of Jurassic Park

Dr. Robert M. Gresham, Contributing Editor | TLT Commentary December 2013

A 65-million-years-old duck-billed herbivore reveals how our science helped life develop.

 

KEY CONCEPTS
• A paper at the 2013 WTC studied the teeth of a 65-million-years-old, duck-billed dinosaur called a hadrosaur or “bulky lizard” in Greek.
• The research showed that the hadrosaur’s teeth were composed of both hard and soft materials that wore unevenly, making them good for grinding vegetation.
• We see the same principle at work today in mammalian animals such as horses, bison and elephants.

While at the fifth World Tribology Congress in September in Turin, Italy, I heard a paper titled “Dinosaur Dentition: Tribology 65 million Years Ago,” by Dr. Brandon Krick, (now at Lehigh University) with Dr. Greg Sawyer from the University of Florida. This was a fascinating presentation that explained phenomena that I have observed but didn’t understand. Further, it is another fine example of how the world of tribology enables and impacts so many of life’s different processes. In this case, a process dating all the way back to the time of dinosaurs remains very relevant today.

As some of you might not know, I have owned a horse or two for many years. I have also had to pay veterinarians to treat the horses’ teeth from time to time. Thus, I have had many opportunities to observe horse teeth and some of the problems they occasionally have. While horses basically have incisors and molars like we do, their teeth look very different than human teeth. Indeed, they function in both a similar but also in a very different manner, since humans are more omnivorous and horses are strictly herbivores. Thanks to Drs. Krick and Sawyer, now I know how and why.

Of course, a little bit of knowledge is always a dangerous thing, so for those requiring greater rigor than I can provide, get it straight from the horse’s mouth, so to speak—the original paper in the journal Science, Oct. 5, 2012, by Krick and Sawyer.

They studied the teeth of a hadrosaur (“bulky lizard” in Greek), a dinosaur that lived between 65 and 140 million years ago during the Cretaceous Period. Hadrosaurs were the family of duck-billed, herbivorous dinosaurs ranging from 10 to 40 feet (3-12 meters). They had horny, toothless beaks and hundreds of cheek teeth in the sides of their jaws. The duck-billed version had the most teeth—nearly a thousand.


Hadrosaurs had no teeth in their bills but hundreds of cheek teeth in the sides of the jaws.

Hadrosaurs were particularly adept at eating large coarse forms of vegetation like tree bark and the like. Greg Erickson, a paleobiologist from Florida State University and collaborator on the study, examined the animal’s behavior and physiology and characterized the hadrosaur as “a walking pulp mill.” So how was the hadrosaur able to accomplish this feat?

Conventional wisdom held that dinosaur teeth are basically dentine and enamel like ours. Part of this conclusion comes from the fact that most reptilian teeth are like that, but then most modern reptiles don’t use their teeth for such grinding. Instead, the researchers found that the dinosaur’s teeth were much more complicated than one might expect. They found six different materials making up the hadrosaur’s teeth. Interestingly, mammalian grinders—horses, bison, elephants and the like—independently but well after the hadrosaurs evolved to a similar kind of structure with four major tissues.

By scratching the different tissues with a very fine diamond- tipped stylus and measuring the abrasion, Krick found that the different tissues had differing resistances to abrasion. Thus, as the tooth underwent wear, the softer parts wore preferentially. This resulted in the surrounding harder areas acting like six levels of a recently sharpened tool. In effect, the tooth surface was, over time, in a dynamic state of change resulting in constant resurfacing of the tooth as it wore. This process kept the surface of the tooth rough in texture with degrees of high hard places and some with hard sharp edges—all good for grinding.

It is this differential wearing that I have noticed in my horses’ teeth. Indeed, often the outer edge of the tooth, over time, becomes very hard and sharp and can even cause ulceration on the walls of the horses’ inner cheek. So the vet grinds these hard sharp edges to prevent this and also levels the teeth so that there is better contact along the line of grinding teeth. Like people, horses’ teeth don’t always align perfectly, which exacerbates the problem. The accompanying photo shows an older horse’s molars with a lot of roughness and some misalignment. Regardless, you can see how the different wear patterns of the four structures tends to cause sharp grinding teeth.


You can see how the different wear patterns of the four structures tends to cause sharp grinding teeth.

Needless to say, I can’t wait for my next vet visit so I can astound him with my little bit of dangerous knowledge. More important, this example serves to illustrate the diverse impact of the field of tribology on the world around us—including the world that existed long before us.

By the way, even though hadrosaurs lived during the Cretaceous Period, the era that succeeded the Jurassic, the title of this article isn’t bad paleontology. A group of hadrosaurs are famously depicted stampeding in the movie “Jurassic Park.” If you’ll recall from the Michael Crichton book, the fictional paleontologists extracted dinosaur DNA from fossilized mosquitoes, and so were able to mix dinosaurs from different geologic periods in their theme park.


Bob Gresham is STLE’s director of professional development. You can reach him at rgresham@stle.org.