Life began in the sea, and it took a long time to move onto land. Plants started creeping ashore about 475 million years ago. Roughly 100 million years later, the first backboned animals followed. For tens of millions of years, those early land animals mainly ate other animals.
Now a fossil from Nova Scotia is changing that timeline.
Scientists at the Field Museum in Chicago, the University of Toronto, Carleton University and the Smithsonian National Museum of Natural History report a 307-million-year-old skull from one of the earliest known land vertebrates that could handle plants. The study appears in Nature Ecology and Evolution.
“This is one of the oldest known four-legged animals to eat its veggies,” says Arjan Mann, assistant curator of fossil fishes and early tetrapods at the Field Museum in Chicago and co-lead author of the study. “It shows that experimentation with herbivory goes all the way back to the earliest terrestrial tetrapods—the ancient relatives of all land vertebrates, including us.”
“The specimen is the first of its group to receive a detailed 3D reconstruction, which allowed us to look inside its skull and reveal its specialized teeth, helping us to trace the origin of terrestrial herbivory,” says Zifang Xiong, a PhD student at the University of Toronto and co-lead author of the paper.
The team named the species Tyrannoroter heberti to honor its discoverer, Brian Hebert. So far, the skull is all anyone has found. Based on related fossils, it likely belonged to a stocky, four-legged animal about a foot long. “It was roughly the size and shape of an American football,” says Mann.
The discovery came from Cape Breton Island, Nova Scotia, where digging can feel like a timed sport.
“Nova Scotia has the highest tides in the world—when we’re working there, we’re racing against the tide, when the ocean comes back in,” says Mann. “It’s very rocky, and the fossils are in cliffs on the shore. Paleontologists hate excavating in cliffs, because the cliff could come down on you.”
Hebert, an avocational paleontologist from Nova Scotia, found the small skull inside a fossilized tree stump. The field season was led by Hillary Maddin, a professor of paleontology at Carleton University.
“The skull was wide and heart-shaped, really narrow at the snout but really wide at the back,” says Mann. “Within five seconds of looking at it, I was like, ‘Oh, that’s a pantylid microsaur.’”
Pantylids sit in an early chapter of life on land. These animals belonged to what scientists call stem amniotes. They were close relatives of the group that later evolved eggs that could stay dry on land. In time, that branch split into reptiles and early mammal ancestors.
“The pantylids are from the second phase of terrestriality, when animals became permanently adapted to life on dry land,” says Mann.
The skull posed a problem: Its mouth had fossilized shut. Mann prepared the fossil by chipping away rock, but key parts stayed hidden. So the team scanned it with CT imaging, stacking X-ray slices into a 3D model.
The scans revealed the most important clue: teeth arranged like a grinding tool kit.
“We were most excited to see what was hidden inside the mouth of this animal once it was scanned—a mouth jam-packed with a whole additional set of teeth for crushing and grinding food, like plants,” says Maddin, the study’s senior author.
Those extra teeth included ones on the roof of the mouth. The team says those opposing tooth batteries could mash tough plant parts, such as mature leaves and stems. The fossil also shows a strong lower-jaw setup, including a single massive tooth near the back that fit against the roof-of-mouth teeth.
“Tyrannoroter heberti is of great interest because it was long thought that herbivory was restricted to amniotes. It is a stem amniote but has a specialized dentition that could be used for processing plant fodder,” says Hans Sues, senior research geologist and curator of vertebrate paleontology at the Smithsonian National Museum of Natural History and co-author of the study.
That does not mean it lived on salad alone.
“When Hans Sues was my advisor during my post-doctoral fellowship at the Smithsonian, he would always say that just about all herbivores alive today consume at least some animal protein, and that herbivory is best seen as a gradient,” says Mann.
The researchers think Tyrannoroter likely ate insects and other small animals, along with vegetation. The team also suggests that crunching insect shells may have helped early land animals develop the ability to process tougher plant material later. Eating plant-eating insects could even have helped seed the gut microbes needed to handle plants.
Modern land ecosystems usually follow a pattern: plants at the base, herbivores above them, and predators at the top. Fossils show that this layered system was taking shape by the Late Carboniferous period.
Still, many researchers argued that widespread plant eating did not fully take off until the Permian period. That idea came from the timing of certain skull, tooth and body traits linked to chewing and to bigger guts that house cellulose-digesting microbes.
The new skull helps explain a long-standing mismatch. Carboniferous landscapes had plenty of plant life, yet clear plant-eating animals seemed scarce in fossils from that time. Some scientists suspected herbivory began earlier than the best-known fossil examples showed. Models supported that hunch, but fossils offered limited proof.
This fossil adds proof, and it also prompted the team to take another look at related animals. The researchers say they found similar herbivory-linked traits in pantylid specimens as old as about 318 million years. That shift suggests early land vertebrates tried plant-heavy diets sooner, and in more lineages, than many people assumed.
The findings sharpen the timeline for when plant eating evolved in land vertebrates, which helps scientists rebuild early food webs on land. It also offers a new case study for how major diet shifts happen, including the role of teeth, jaws and gut microbes.
The research adds another data point for understanding how plant-eating animals respond when ecosystems change quickly. “At the end of the Carboniferous, the rainforest ecosystems collapsed, and we had a period of global warming,” says Mann. “The lineage of animals that Tyrannoroter belongs to didn’t do very well. This could be a data point in the bigger picture of what happens to plant-eating animals when climate change rapidly alters their ecosystems and the plants that can grow there.”
The findings may guide future fossil searches by highlighting tooth patterns that can signal diet, even when stomach contents do not survive.
Research findings are available online in the journal Nature Ecology & Evolution.
The original story “Fossil skull discovery reveals when land animals first learned to eat plants” is published in The Brighter Side of News.
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