Scientists from China, the US and Canada found the fossilised jawbone of Sinosaurus, presumed to have existed 190 million years ago, and concluded that it could be the earliest discovered animal that had a toothache.
The scientists held a dental consultation on the dinosaur, taking X-rays and writing a report on its toothache, which was published in Chinese Science Bulletin last week.
The extinct animal earlier could have developed a toothache after biting into something hard that it damaged its gum, according to the study.
"It was common for carnivorous dinosaurs to lose teeth, but this specimen we were studying was different," Xing Lida, who co-authored the research report.
"Its tooth socket was completely filled, which indicates the tooth loss was because of dental problems instead of external force," Xing told state-run China Daily here today.
In 2007, the Lufeng Dinosaurian Museum recovered an incomplete skull and several postcranial fragments of a new specimen of Sinosaurus from Lufeng Basin in Yunnan province.
Based on other Sinosaurus specimens, the complete upper jaw should have 13 or 14 tooth positions.
The skeleton had two broken teeth preserved in the tooth socket.
An X-ray of the bone shows the outline of the original tooth socket.
The space of the bad tooth is less radiolucent than the adjacent tooth socket - in other words, X-rays don't pass through as much - which indicates that secondary bone filled the space, the report said.
"When the dinosaur's teeth were lost or removed while it was alive, the bony socket remodelled over time, so that there was no longer a tooth socket," Xing said.
Scientists also found no pyrite rot in the socket of the bad tooth, while pyrite growth was observed over all the other tooth spaces.
"The osseous abnormalities after teeth loss is common among mammals, but it is rarely found on reptiles like the dinosaur," professor Bruce M Rothschild, at the University of Kansas Natural History Museum and Biodiversity Research Institute said, in a news release about the research report, which he also co-authored.
Canadian paleontologist Phil R Bell compared the Sinosaurus jawbone to a skeleton of a ring-tailed lemur because the ring-tailed lemur likes chewing hard nuts, which causes teeth problems similar to those of the Sinosaurus.
"The dinosaur might have hurt its teeth and got the teeth problem for similar reasons," Bell said in the news release.
"The study of disease and other abnormalities in the fossil record can reveal unique insights into the behaviour, biology and development of extinct animals.
"For example, among theropod dinosaurs, injury-related trauma like bites, exostoses, fractures, infection and stress fractures are the overriding cause of osteopathy," he said.
