Taeniodonta

Taeniodonta is an extinct order of eutherian mammals. The name means "banded teeth." These animals lived in North America and Europe. They existed from the late Cretaceous period until the middle Eocene. They were significant because they were among the first mammals to evolve large body sizes. Some reached sizes comparable to a modern wild boar. Others grew as large as an American black bear.

Scientists classify taeniodonts into two main families. The first is Conoryctidae. This is a paraphyletic family of small to medium animals. They weighed between 5 and 15 kilograms. They had generalized body forms. Their cheek teeth had hypsodont crowns. These are high-crowned teeth used by plant-eaters. These fossils disappear from the record before the Eocene begins.

The second family is Stylinodontidae. This is a monophyletic family of medium to large animals. Their weight ranged from 10 to 110 kilograms. They evolved much larger bodies very quickly. They had huge, compressed, and recurved claws on their middle toes. Their forelimbs were adapted for digging. Later genera, such as Stylinodon, possessed teeth that grew continuously.

The feeding mechanism of stylinodonts was very unique. Their faces were unusually short. They had massive jaws and large attachments on the skull for chewing muscles. Their front teeth were curved and ever-growing. These teeth had enamel only on the outside surface. Because enamel is harder than the rest of the tooth, the tooth wears at an angle. This creates a battery of self-sharpening chisels. Modern rodents use a similar method. However, stylinodonts used their canines instead of incisors to achieve this.

Their rear teeth were also specialized. These molars became ever-growing pegs. The enamel was restricted to bands on the sides of the tooth. While root hypsodont molars are usually for hard vegetable food, enamel loss makes the tooth softer. Stylinodont molars could crush food but could not grind it. They did not use high-pressure chewing at the back of the mouth like modern horses or elephants. Instead, they moved more of their chewing power to the front teeth.

We can learn about their behavior from their anatomy. A preserved braincase of Onychodectes tisonensis shows a flat cerebrum. The cerebrum is the part of the brain used for higher functions. It lacked convolutions, which suggests limited intelligence. However, they had very large olfactory bulbs. These are the parts of the brain used for smelling. This suggests taeniodonts relied heavily on their sense of smell. Their forelimb adaptations also prove they were strong diggers.

Taeniodonts were likely basal placental mammals. A 2022 study by Bertrand and Shelley suggests they are not closely related to any living family. They may have been among the first specialist mammals in upland areas. They likely sought hard-coated plants and fruits in hothouse environments. Eventually, they disappeared from the fossil record. This coincided with the appearance of the first pig-like artiodactyls. These new mammals were faster and more intelligent. They could also grind food more effectively, which may have led to the extinction of the taeniodonts.