“Tyrant farmer”. The first vegetarian, related to humans, lived 300 million years ago

Tetrapod found in Canada rewrites the history of terrestrial herbivores: “experience” with herbivory may have begun much earlier.

A fossil more than 300 million years old, discovered in what is now Nova Scotia, Canada, is changing the known chronology of when land vertebrates began eating plants.

The species, described as Tyrannoroter hebertimay be among the oldest tetrapods with clear signs of adaptation to a diet with a high plant component, in a period long before the emergence of dinosaurs, according to a study in Nature Ecology & Evolution.

The discovery is based on an exceptionally well-preserved skull found embedded inside a fossilized trunk on the island of Cape Breton. According to the researchers, cited by , the anatomy reveals a set of dental characteristics compatible with the crushing and cutting of fibrous plant material, a dietary strategy that was believed to have emerged later in the evolution of vertebrates on dry land.

Plants would have colonized terrestrial environments about 475 million years. However, for tens of millions of years, the first animals to explore the earth would have been mostly carnivorous and not very diverse. The new discovery suggests that the “Experimentation” with herbivory may have begun much earlier among the first tetrapods, ancient relatives of all living land vertebrates, including humans.

The skull of Tyrannoroter it measures around 10 centimeters, approximately a third of the animal’s body, according to the authors’ estimates. The general appearance is described as similar to that of a small lizard, although the animal predates the evolutionary separation between the branches that would later give rise to reptiles and mammals. The scientific name literally means “tyrant farmer”.

To analyze the interior of the skull, sealed by fossilization, the team used high-resolution computed tomography. The images revealed dense groupings of oppositely arranged teeth on the roof of the mouth and lower jaw. This configuration would allow cutting, crushing and grinding of tough foods, such as leaves and stems, in an adaptation reminiscent of much later herbivores, including some dinosaurs.

The authors argue that these structures indicate that the adaptations necessary to process fiber-rich vegetation emerged quickly after terrestrial colonization by vertebrates. Furthermore, similar features have been identified in fossils dating back to around 318 million years, suggesting that herbivory may have spread relatively quickly among some early groups of tetrapods.

Still, scientists admit that Tyrannoroter may not have been exclusively vegetarian. Like many modern herbivores, it is plausible that it supplemented its diet with insects or small prey. The ability to crush exoskeletons may even have functioned as an evolutionary step to later deal with tougher plants; and the consumption of herbivorous insects could have facilitated the acquisition of intestinal microorganisms capable of helping to digest cellulose.