The Dawn of Plant-Eating: Uncovering Tyrannoroter heberti, an Early Terrestrial Herbivore

Life on Earth began in the oceans. Plants started colonizing land approximately 475 million years ago, with the first land animals with backbones appearing about 100 million years later. For tens of millions of years, these early terrestrial vertebrates consumed only other animals.

A Groundbreaking Discovery: Tyrannoroter heberti

A new paper describes the 307-million-year-old fossil of one of the earliest known land vertebrates to have evolved the ability to eat plants: Tyrannoroter heberti.

This species has been named Tyrannoroter heberti, in honor of its discoverer, Brian Hebert.

Based on its skull and the more complete skeletons of its relatives, Tyrannoroter was likely a stocky, four-legged creature about a foot long, roughly the size and shape of an American football. It was one of the largest land-dwelling animals of its time. Tyrannoroter is classified as a stem amniote, an ancient relative of all land vertebrates, including mammals and reptiles.

Unearthing the Past: Location and Classification

The fossil was discovered by avocational paleontologist Brian Hebert on Cape Breton Island, Nova Scotia. The small skull was found within a fossilized tree stump during fieldwork conducted under challenging conditions, including high tides and rocky shore cliffs.

Upon examination, the skull was identified as belonging to a pantylid microsaur, a group representing the second phase of terrestrial adaptation, where animals became permanently adapted to life on dry land.

Dental Clues: Evidence of Early Herbivory

Researchers carefully prepared the specimen and utilized CT scanning to examine the internal structures of the skull, as its mouth had fossilized closed. The CT scans revealed a mouth densely packed with specialized teeth designed for crushing and grinding food, including additional teeth on the roof of its mouth. These dental features indicate that Tyrannoroter heberti possessed the capacity to process plant matter.

This discovery challenges previous understanding, suggesting that stem amniote tetrapods developed specialized dentition for plant consumption earlier than scientists had believed.

Senior research geologist Hans Sues noted the significance, as it was long thought that herbivory was primarily restricted to amniotes.

A Varied Diet and Lessons from the Past

While Tyrannoroter demonstrated the ability to consume plants, it likely had a varied diet that also included smaller animals, such as insects. It is hypothesized that the consumption of insect exoskeletons by early tetrapods may have facilitated the development of the ability to process tough plant materials. Furthermore, digesting plant-eating insects could have provided the necessary gut flora and microbes for plant digestion.

The research also provides insights into the impact of ecosystem changes on plant-eating animals. Tyrannoroter lived towards the end of the Carboniferous Period, a time characterized by significant climate change, including the collapse of rainforest ecosystems and global warming. The lineage to which Tyrannoroter belongs did not thrive during this period, offering a historical data point on how plant-eating animals respond to rapid environmental alterations.