October 5, 2012
Toothy Tale – Hadrosaurids Could Pulverize Plants With Their Teeth
April Flowers for redOrbit.com - Your Universe Online
A new study has found that duck-billed dinosaurs had an amazing capacity to chew tough and abrasive plants with grinding teeth more complex than those of modern grazers. The study, published in Science, is the first to recover material properties from fossilized teeth.The dinosaurs, also known as hadrosaurids, were the dominant plant-eaters during the Late Cretaceous — about 85 million years ago — in the areas now known as Europe, North America and Asia. With up to 1,400 teeth situated in broad jaws, hadrosaurids were previously thought to have chewing surfaces similar to other reptiles, comprised of just two tissues — enamel, a hard hypermineralized material, and orthodentine, a soft bonelike tissue. Scientists have suspected that they were not that simple, however.
"We thought for a long time that there was more going on because you could just look at the surface of the tooth and see advanced topography, which suggests that there are many different tissues present," said Mark Norell, chair of the American Museum of Natural History's Division of Paleontology.
A team of scientists and engineers engaged in some novel experiments to investigate the dinosaurs' dental structure and properties. The fossilized teeth were sectioned and microscope slides were made from them, which revealed that hadrosaurids had six dental tissues instead of the expected two. Six tissues put the hadrosaurids with four more than reptiles and two more than expert mammal grinders like horses, cows and elephants. The researchers determined the differential hardness and wear rates of the dental tissues using a technique called nanoindentation in which a diamond-tipped probe mimics the grinding of abrasive food by being indented and/or drawn across the fossilized teeth.
Gregory Erikson, biology professor at Florida State University said, "We were stunned to find that the mechanical properties of the teeth were preserved after 70 million years of fossilization. If you put these teeth back into a living dinosaur they would function perfectly."
The hadrosaurid's teeth include giant tubules and a thick mantle dentine, along with the four tissues found in mammalian teeth: enamel, orthodentine, secondary dentine that helps prevent cavities and coronal cementum that supports the teeth's crests. The two additional tissues are thought to be an added protection against abscesses. The dental tissue distribution in hadrosaurids greatly varied in each tooth, unlike a mammals tooth.
The extra tissues and the varied distribution together suggest that hadrosaurids evolved the most advanced grinding capacity known in vertebrate animals. The study authors say this might have led to their extensive diversification.
The advanced tissue modification in the duck-billed dinosaurs appears to have allowed them to radiate into specialized ecological niches where they ate extremely tough plants like fern, horsetail and ground cover. These plants would have been much more difficult fare for dinosaurs with shearing teeth.
Norell said, "Their complex dentition could have played a major role in keeping them on the planet for nearly 35 million years."
The findings also provide strong evidence that dental wear properties are preserved in fossil teeth, opening the door for more studies on the dental biomechanics of fossils from other wide-ranging groups of animals to better understand evolutionary modifications in diet.
Image 2 (below): This photo shows the horse-like chewing surface in a hadrosaurid dental battery. The crests and basins form through differential wear of the dental tissues. Credit: G. M. Erickson/Florida State University