Russian paleontologists have studied the upper molar tooth structure of the Kielantherium mammal, which had lived in the early Cretaceous period and have made an interesting conclusion – this animal was one of the first mammals, who learned to chew food. The tooth structure is still very primitive, thus scientists can certainly announce the discovery of an intermediate stage between “biting” and “chewing” mammals. The unique finding of the Russian scientists is described in the Science journal and allows making essential corrections in the early mammalian evolution theory.

Many humans start thinking about their teeth only after they visit their dentist or after they see the toothpaste ad for thousand times. But paleontologists consider teeth structure and animal dentition to be very important. These parameters not only help to identify an animal, they also give information on its way of life, its parents and descendants, its history and evolution. Moreover, teeth are sometimes the only things, describing terrestrial mammals, which are found during the diggings.

Animal dentition shows that while first mammals could only bite food and swallow it, their descendants have thoroughly chewed food before swallowing. This habit appeared to be useful, because it raised food efficiency. How did animals learn to chew? They had to invent upper and lower molar teeth - first serve as pestle and others – like mortar. Mammals have come a long way, before such system appeared – who was the first to use the chewing technology? Scientists have recently found possible candidate for the breakthrough.

The animal was found in stores of the Institute of Paleontology, where it has spent not less than 30 years – the remains of the upper molar tooth of the Kielantherium mammal, found in the lower Cretaceous deposits (100-120 million years old) in the Gobi desert. Russian scientists from Moscow and Saint Petersburg have found the remains, and described them in the famous Science journal. The research fellows think that Kielantherium belonged to the mammalian group, which was first to start chewing food – one molar tooth appeared to be enough for making corrections in the mammalian evolution theory.

Previous evolution theory suggested following hypothesis – Kielantherium‘s relatives were thought to be ancestors of marsupial mammals, and placental mammals were considered to separate from this branch earlier. However, Kielantherium's molar tooth showed some resemblance with teeth of placental mammals – it appears that chewing ability was formed in the early Cretaceous period in some common ancestor of both marsupial and placental mammals, and their separate evolution have started later. This theory can cause some hard and serious work on correcting the mammalian phylogenetic tree.

Sources:

Alexey V. Lopatin, Alexander O. Averianov. An Aegialodontid upper molar and the evolution of mammal dentition // Science, 2006, vol. 313, p. 1092.
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Anna Kizilova