A hadrosaurid dental battery. The different crests and basins of the chewing… (Gregory M. Erickson / Florida…)
The duck-billed dinosaurs called hadrosaurids sported hundreds of bewilderingly complex teeth that were optimized for grinding away at the fibrous plants they ate, according to a new study.
The hadrosaurids' teeth are made of six distinct materials, according to the report, published Thursday by the journal Science. That makes the teeth far more complex than humans', which are primarily made of two materials, enamel and orthodentine. They are even more complex than the teeth of horses and buffalo, which are made of four materials and also evolved to grind away at plant matter. The hadrosaurids have what scientists call a "dental battery," meaning they have hundreds of teeth that work together when they eat, with new teeth "erupting" into the mouth all the time.
The scientists, led by Greg Erickson of Florida State University, had noticed that the tooth fossils they had of hadrosaurids showed the type of "self-wear" seen in horse and buffalo teeth, where grinding of the teeth against plants leads teeth to change in shape and become ever more effective chompers. This effect generally requires a diverse array of materials within the teeth, something scientists had yet to demonstrate with hadrosaurids even though the fossils had all the signs of self-wear, including crests and basins across the chewing surface.
In addition to an outer coating of enamel and internal orthodentine, the hadrosaurid teeth also had two other types of dentine of varying hardness, as well as a material called giant tubule and a material called cementum.
In our teeth, cementum plays a bit role helping a tooth stay fixed to a root. But in the hadrosaurid teeth, cementum is found throughout the tooth, helping to strengthen and support exposed portions of the tooth that might otherwise chip while grinding hard plant matter. All six materials and the different ways they wore down played a role in the dinosaur's ability to grind and eat plant matter.
The researchers found that the distribution of different materials throughout the teeth meant that as new teeth erupted, the different stages of wear of different teeth led to an ever-changing, dynamic chewing surface that worked much like a nail file.
As part of the study, the group measured the hardness of each of the materials present in the tooth. With this information, they created a 3-D model of the hadrosaurid tooth that showed how they would wear down from eating, beginning with the first exposure of the chewing surface. The model closely matched the fossils.
The scientists believe the complexity of the dinosaur's dentition contributed greatly to its success -- the hadrosaurids are believed to have been the dominant herbivore of their era, with populations spread across present-day Asia, North America, and Europe.
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