Paleontologists from the University of Bonn (Germany) have managed to reconstruct the chewing movement of an early mammal that lived almost 150 million years ago.
This showed that his teeth worked extremely precisely and surprisingly efficiently. However, it is possible that this aspect proved to be a shortcoming during evolution.
With only twenty centimeters in length, the smallest weasel is today considered the smallest living beast in the world. It is unlikely that the mammal researched by the University of Bonn was now larger. However, the species to which it belongs is long extinct: Priacodon fruitaensis (scientific name) lived almost 150 million years ago, at a time when dinosaurs dominated the animal world, and the triumph of mammals was yet to come.
In their study, paleontologists from the Institute of Geosciences at the University of Bonn analyzed parts of the bones of the upper and lower jaws of the fossil sample. More precisely: cheek teeth (molars). Because experts can say a lot, not only about the animal’s diet, but also about its position on the family tree. In P. fruitaensis, each molar is barely larger than one millimeter. This means that most of their secrets remain hidden from the naked eye.
Therefore, researchers from Bonn used a special tomography method to produce three-dimensional images of teeth in high resolution. They then analyzed these micro-CT images using a variety of tools, including special software jointly developed at the Bonn-based institute. “Until now, it was not clear how the teeth in the upper and lower jaw fit together,” explains prof. Thomas Martin, who chairs the Department of Paleontology at the University of Bonn. “We could answer that question now.”
How did creatures chew 150 million years ago?
The upper and lower jaws contain several molars. In mammalian precursors, the molar 1 of the upper jaw would bite exactly on the molar 1 of the lower jaw when chewing. In more developed mammals, however, the rows of teeth are shifted toward each other. The molar 1 at the tip therefore strikes exactly between the molar 1 and the molar 2 when bitten, so that it comes into contact with the two molars and not with one. But how was it in the early mammal P. fruitaensis?
“We compared both options on a computer,” explains Kai Jäger, who wrote his doctoral thesis in Thomas Martin’s research group. “This showed that the animal was bitten like a modern mammal.” The researchers simulated the entire chewing movement for both alternatives. In the more original version, the contact between the upper and lower jaws would be too small for the animals to efficiently crush food. This is different with the “modern” alternative: in this case, the cutting edges of the molars slid side by side when chewed, like the scissor blades used today for art and craft.
Therefore, his tooth had to make it easier for P. fruitaensis to cut the flesh of its prey. However, the animal was probably not a pure carnivore: its molars have cone-shaped elevations, similar to mountain peaks. “Such nodules are especially useful for perforating and crushing insect caps,” says Jäger. “Therefore, they are also found in today’s insects.” However, the combination of carnivorous teeth and insectivores is probably unique in this form.
The tips are noticeable in other ways as well: They are practically the same size in all molars. This made the toothpick extremely precise and efficient. However, these advantages came at a price: small changes in the structure of the nodules would probably dramatically worsen the chewing. “This potentially hindered the development of the dental appliance,” says Jäger.
This species of tooth has actually survived almost unchanged in certain lineages of evolutionary history over a period of 80 million years. At one point, however, its owners became extinct – perhaps because their teeth could not adapt to changing food conditions.
Header image – Examined tooth P. fruitaensis. The upper molars (M2, M3) were moved from the lower ones (m2, m3). This causes the tips to merge in a way that creates a sharp blade. Image credit: Thomas Martin, Kai RK Jäger / University of Bonn