Suminia, however, developed a much more advanced way of eating. Microscopic analysis of the reptile's teeth revealed marks indicating that Suminia used its back teeth to chew with a shearing motion that enabled it to shred plant material more effectively.
The researchers said the skull, which was discovered in 1990 in central Russia, looks like that of a monkey or a rodent, with huge eyes and large, distinctive teeth. Dating techniques indicate the animal lived in the Paleozoic era, about 260 million years ago.
"Suminia is the best example we have from such an early era of an animal that is adapted to high-fiber herbivory," said Rybczynski. "It was clearly more specialized to eat coarse, fibrous food than anything else of the time."
Common Trait of Mammals
Developing a more advanced system of chewing enabled ancient herbivores and their descendants to increase their intake of food and process it more efficiently. By shredding leaves into small bits before swallowing, they can absorb the maximum amount of energy and nutrients in the plants they eat.
A class of reptiles related to Suminia, called dicynodonts, were the first successful land-dwelling and plant-eating vertebrates, which means they were probably also efficient in processing their food, the researchers said. But dicynodonts had beaks rather than teeth, so they technically were not able to chew.
In contrast, Suminia's teeth were highly pronounced and similar to the teeth of some plant-eating reptiles and dinosaurs.
"What is immediately striking about this animal is that it has really large teeth and they occlude, or meet," Rybczynski said. "This is unlike iguanas, crocodiles, and most other non-mammalian vertebrates, whose teeth don't even touch. Since the teeth occluded, we knew that Suminia had some sort of specialized chewing mechanism."
Today, mammals are the animals that chew their food, particularly plants, most intensively. Suminia was distantly related to a class of reptiles that eventually evolved into mammals.
The researchers speculate that an advanced chewing ability is tied to the "warm-blooded" nature of mammals (and perhaps dinosaurs).
To maintain a high body temperature and high metabolism, mammals need an efficient way to digest and absorb nutrients from food. In contrast, "cold-blooded" animals, such as modern-day lizards and many of their ancient reptile ancestors, do not have the same energy requirements.
Herbivores that lack a well-developed chewing ability tend to eat the more tender leaves, flowers, and buds of plants, Rybczynski said. Minimal oral processing of vegetation is associated with a slower rate of digestion. The iguana, for example, swallows vegetation and allows it to digest for a long time.
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