Formerly mammals with astonishingly precise bite

denture

Jaw and bite of Priacodon fruitaensis. (Photo: Thomas Martin, Kai RK Jäger / University of Bonn)

The teeth and jaws of early mammals reveal a lot about their way of life, diet and evolution. Researchers have now analyzed the teeth of a tiny predator that lived in the northern hemisphere around 150 million years ago. Priacodon fruitaensis was able to bite with amazing precision. The chewing strips, which were provided with even humps, matched each other perfectly and could chop both meat and insects. But it was precisely this perfect pine architecture that ensured that small deviations resulted in major disadvantages. That reduced the evolutionary flexibility.

Most of the teeth and jaws of many of the early mammals that populated the earth at the same time as the dinosaurs are preserved. The scientific system of these animals is therefore often based primarily on their teeth. However, little is known so far about how the chewing apparatus of the respective specimens actually worked. A group of these primeval mammals are the Triconodontidae, named after three even cusps that they have on each of their molars.

Bite like today’s mammals

Researchers led by Kai Jäger from the Rheinische Friedrich-Wilhelms-Universität Bonn have now reconstructed how the Triconodontidae probably chewed. To do this, they analyzed the teeth of the primeval predator Priacodon fruitaensis, which were only a few millimeters in size, with the help of micro-computer tomography and 3D models. “Up until now it was unclear exactly how the teeth in the upper and lower jaw interlock,” explains Jäger’s colleague Thomas Martin. “We have now been able to answer this question.”

In the first mammalian ancestors, the molars in the upper and lower jaw were arranged exactly opposite one another. In today’s mammals, on the other hand, they are slightly shifted from one another, so that each molar engages between two opposing teeth – virtually on a gap. In order to clarify which tooth scheme applies to Priacodon fruitaensis, the researchers simulated the chewing movements for both variants. “It showed that the animal bit like a modern mammal,” says Jäger. Otherwise the contact between the upper and lower jaw would have been too little to efficiently chop up the food.

Carnivores and insectivores

With an estimated body weight of only 40 to 60 grams, Priacodon fruitaensis is just about the size of a mouse weasel, the smallest predator living today. How did it feed in a time when giant dinosaurs ruled the earth? The teeth also provide information about this: the perfectly coordinated, mutually displaced chewing strips enable meat to be cut up almost as if with scissors. At the same time, the molars also have the cusps typical of Triconodontidae. “Such humps are particularly well suited to perforating and crushing insect shells,” explains Jäger. “They are therefore also found in today’s insectivores.”

The unique combination of characteristics put the primeval predator in a position to eat other small mammals as well as insects. The cusps on the molars enabled the Triconodontidae to eat a wide variety of foods. Since the bumps were all nearly the same size, they made chewing very precise and efficient. With just a single bite, a hard insect shell could be broken into many small pieces. But the perfect match had a disadvantage: Small changes in the shape of the cusps would have worsened the chewing performance so much that individuals with such a variation would have had significantly lower chances of survival and reproduction. “That may have made it difficult to develop the dental system further,” says Jäger.

Mammals with less uniform teeth, on the other hand, had greater evolutionary flexibility, which enabled them to adapt to changing feeding conditions. In the course of evolution, this variant prevailed over the more efficient but inflexible.

Source: Kai Jäger (Rheinische Friedrich-Wilhelms-Universität Bonn) et al., Scientific Reports, doi: 10.1038 / s41598-020-79159-4

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