January 23, 2021

Sunday Vision

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Early mammals with remarkably accurate sting – everyday heritage

Paleontologists at the University of Bonn (Germany) succeeded in reconstructing the chewing movement of an early mammal that lived about 150 million years ago.

This showed that his teeth were operated with surprisingly high precision. However, it is possible that this particular aspect is a flaw in the course of evolution.

At just twenty centimeters long, the smallest weasel is considered the world’s smallest carnivore alive today. The mammals that the researchers at the University of Bonn studied were unlikely to be larger. However, the species to which they belong became extinct long ago: Priacodon fruitaensis (scientific name) lived nearly 150 million years ago, at a time when dinosaurs dominated the animal world and a mammalian victory was still to come.

In their study, paleontologists from the Institute of Geosciences at the University of Bonn analyzed parts of the upper and lower jaw bones of a fossil sample. More precisely: his cheek teeth (molars). Because experts can learn a lot from it, not only about the animal’s diet, but also about its position in the family tree. In P. fruitaensis, each molar is barely more than one millimeter. This means that most of their secrets remain hidden from the unarmed eye.

So the researchers from Bonn used a special tomography method to produce high-resolution 3D images of the teeth. They then analyzed the CT images using various tools, including special software jointly developed at the Bonn-based institute. Professor Thomas Martin, who holds the chair of palaeontology at the University of Bonn, explains: “Until now, it was not clear exactly how the teeth in the upper and lower jaws fit together.” “We have now been able to answer that question.”

How did creatures chew 150 million years ago?

Both upper and lower jaws contain multiple molars. In mammalian ancestors, the 1 molar of the upper jaw was bitten precisely on the molar 1 of the lower jaw when chewing. However, in more advanced mammals, the rows of teeth are shifted against each other. The molar 1 hits exactly on top between molar 1 and molar 2 when bitten, so that it comes into contact with two molars instead of one. But what were things like in the early mammals P. fruitaensis?

“We compared both options on the computer,” explains Kay Jagger, who has written the doctoral thesis for the Thomas Martin Research Group. “This showed that the animal was biting like a modern mammal.” The researchers fully simulated the chewing motion of both alternatives. In the original version, the contact between the upper and lower jaws was too small for animals to efficiently crush food. This differs with the “more modern” alternative: in this case, the edges of the severed molars slipped in front of each other when chewing, like the blades of the pink scissors that children use today for arts and crafts.

So its teeth must have made it easier for P. fruitaensis to cut the flesh of its prey. However, the animal was probably not a pure carnivore: its molars have conical heights, resembling mountain tops. “These porches are especially useful for drilling and crushing insect shields,” says Jäger. “Therefore it is also found in insectivores today.” However, the combination of carnivorous and insectivorous teeth is perhaps unique in this form.

Balconies can also be noticed in other ways: they are approximately the same size across all molars. This made the teeth very accurate and effective. However, these advantages came at a price: small changes in the structure of the terraces probably greatly degraded their chewing performance. “This potentially makes it more difficult for the dental system to develop,” says Jäger.

This type of tooth has in fact remained virtually unchanged in certain lineages of evolutionary history over a period of 80 million years. But at some point, their owners became extinct – perhaps because their teeth couldn’t adapt to the changing dietary conditions.

Bonn University

Banner photo – examined teeth for P. fruitaensis. The upper molars (M2, M3) are compensated for the lower molars (M2, M3). This interlocks the fringes in a way that creates a sharp cutting edge. Image Credit: Thomas Martin, Kai RK Jäger / University of Bonn