April 19, 2011

Evolution Meant Toothaches For Ancient Reptiles

A reptile that lived 275 million years ago in present day Oklahoma is giving paleontologists a glimpse of the oldest known toothache, predating by 200 million years the previous record for the earliest known evidence of tooth decay in a terrestrial vertebrate.

The researchers, led by Professor Robert Reisz, who chairs the Department of Biology at the University of Toronto Mississauga, found evidence of bone damage due to oral infection in Paleozoic reptiles as they adapted to living on land. 

"Not only does this fossil extend our understanding of dental disease, it reveals the advantages and disadvantages that certain creatures faced as their teeth evolved to feed on both meat and plants," said Reisz.

"In this case, as with humans, it may have increased their susceptibility to oral infections."

The researchers investigated the jaws of several well-preserved specimens of Labidosaurus hamatus -- an omnivorous, 30-inch long terrestrial reptile -- that lived in North America 275-million-years ago.

One "exquisitely preserved" specimen found near Coffee Creek, Texas, stood out because of missing teeth and associated erosion of the jaw bone.  Using CT-scanning, Reisz and colleagues found evidence of a massive infection, which resulted in the loss of several teeth, as well as bone destruction in the jaw in the form of an abscess and internal loss of bone tissue.

As the ancestors of advanced reptiles adapted to life on land, many evolved dental and cranial specializations to feed more efficiently on other animals and to incorporate high-fiber plant leaves and stems into their diet. The primitive dental pattern, in which teeth were loosely attached to the jaws and continuously replaced, changed in some animals. Instead, teeth became strongly attached to the jaw with little or no tooth replacement.

This was clearly advantageous to some early reptiles, allowing them to chew their food and improve nutrient absorption. The abundance and global distribution of Labidosaurus suggest that it was an evolutionary success.

The researchers theorize that as this reptile lost the ability to replace teeth, the likelihood of infections of the jaw from damage to the teeth increased dramatically.  This is because prolonged exposure of the dental pulp cavity of heavily worn or damaged teeth to oral bacteria was much greater than in other animals that quickly replaced their teeth.

Reisz noted that human susceptibility to oral infection has some parallels to those of ancient reptiles that evolved to eat a diet incorporating plants in addition to meat.

"Our findings suggest that our own human system of having just two sets of teeth, baby and permanent, although of obvious advantage because of its ability to chew and process many different types of food, is more susceptible to infection than that of our distant ancestors that had a continuous cycle of tooth replacement," he said.

The study was published online in the journal The Nature of Science.


Image 1: Fossil of Labidosaurus hamatus. Courtesy Wikipedia (CC BY-SA 3.0)  


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