Studies involving Professor Robert Reisz, a paleontologist at Toronto Mississauga University, appear in recent issues PLOS ONE in Proceedings of the Royal Society B.
In the first article, Reisz and his colleagues at the University of Jilin, China, examined teeth Changchunsaurus parvus, a small vegetable dinosaur from the Cretacean period.
Ornithic ("avant-garde") dinosaurs have developed an incredible variety of teeth, including complex dental accumulators from derived ornithopods (such as known dinosaurs of duck), but little is known about how these complex arrangements originated from simple dental arrangement of early dinosaurs. Changchunsaurus parvus belongs to the branch on or near the original ornitopods, so it can provide an insight into the development of an early ornithological tooth.
In this study, Reisz and his colleagues found a unique method of swapping teeth that enabled Changchunsaur to recycle teeth without disturbing the permanent shear surface formed by her tooth line. The authors also find that teeth have a wavy enamel, a type of tissue that previously thought that it developed only in more modern ornithopods. The authors assume that these features may have already happened, as this group of dinosaurs has become specialized in plant nutrition.
Complete teeth: how mammals have developed their unique tooth anchoring system
In another study, published in Proceedings of the Royal Society BReisz worked with his students who are now at the University of Alberta and the University of British Columbia, as well as associates at the University of Washington in Seattle and Unidad Ejecutor Lillo in Argentina.
Anyone who has worn carriers knows that your teeth can slowly swing and pull to their right spots. You can not know that this movement is enabled with a special conjunction that has all the teeth in its socket. This ligament also serves to alleviate every tooth when we chew food. The origin of this ligament was a mystery.
This study, conducted by the former University of Toronto Mississauga Ph.D. student Aaron LeBlanc, solved the secret of how mammals developed their complex dental system. For over a century now, scientists thought that this ligament appeared in the first mammals when they first began to chew, but this new article suggests that this system first appeared in extinct mammalian relatives called terapseids.
LeBlanc and his colleagues, with a review of CT scanning and the production of thin parts of fossil therapeutic teeth and jaws, found that mammals' teeth are not as unusual as we used to think. "We found evidence of this linkage system in several groups of extinct therapy, which told us that it developed before the first mammals chewed their food," LeBlanc says.
Researchers also think that they have figured out how our therapeutic ancestors developed this anchor system. They found that in many fossil synapsids, dental bones rapidly conditioned with this bone, but in some therapies, the natural bone is growing more slowly.
"We have found that some therapiids, such as mammals, have to develop this anchor system rather than by developing completely new tissues, but by delaying the growth of the round bone," says Reisz. We believe that mammals are more "advanced" than other extinct therapies, but instead of mammals teeth frozen in the previous state of development compared to animals with teeth attached to the jaw. "
Both studies at Toronto Mississauga University include teeth that are not firmly anchored in the jaw, but in contact with the ligaments. Now there is clear evidence that the ligaments are present in carnivorous and herbivores of dinosaurs and mammals, and these ligaments are not necessarily associated with the evolution of chewing, as previously thought. Reisz hopes that ongoing research will continue to reveal a better understanding of this interesting enigma.
The teeth of the homo antecessor illuminate the trends in the development of the dental development of pleistocene hominine
Chen J, LeBlanc ARH, Jin L, Huang T, Reisz RR (2018) Microstructure for the development of teeth, histology and enamel in Changchunsaurus parvus: Implications for the development of teeth in ornithotic dinosaurs. PLOS ONE 13 (11): e0205206. doi.org/10.1371/journal.pone.0205206