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Hundreds of millions of years ago, life began on Earth, likely somewhere in the oceans. For a long time, the oceans were the only place where life existed, and that worked out quite well.
Over time, some plants that grew near the edges of the oceans would adapt to be able to survive outside the water during low tides, and then eventually to survive entirely outside the water.
Naturally, that eventually led to the land being covered with all sorts of different plants. These plants enjoyed a long period where they could largely live in peace, but eventually animals started crawling their way out of the water too, and everything changed.
Initially, it was just the insects that evolved to consume plants. Any four legged animals, such as reptiles, would be carnivorous. It was previously thought that this was the case for a very long time, but a new study published in the journal Nature Ecology & Evolution looked at the fossil of a 307-million-year-old dinosaur that was a herbivore.
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The fossil was from a Tyrannoroter heberti, which is now the earliest terrestrial vertebrate known. Co-lead author of the study, Arjan Mann, is an assistant curator of fossil fishes and early tetrapod’s at the Field Museum in Chicago, explained:
“Insectivory was likely a preadaptation for herbivory. Tetrapod’s eating early herbivorous insects secondarily acquired the gut flora needed to process plant material because insects were the first to eat plants (evidenced from feeding damage on plant fossils).”
This is an interesting evolutionary strategy that involves the introduction of outside gut bacteria that ended up helping the animal. When the ancestors of the Tyrannoroter consumed insects that had been eating plants, the gut bacteria from the insect became the gut bacteria of the small dinosaur.
It is likely that the dinosaur would also get bits and pieces of leaves while catching the insects, so having the ability to digest them and get nutrients from them was a benefit to their survival.
Over the course of many generations, this would eventually mean that the digestive system of the Tyrannoroter could process plants and extract their nutrients, eventually leading them to become herbivores. Mann goes on to say:
“This paper reveals the earliest evidence of terrestrial herbivory in tetrapods, animals with four limbs – a group that includes humans. The age of the fossils presented in this paper, not just Tyrannoroter (~307 Ma), but also older fossils from Joggins, Nova Scotia (318 Ma) indicate herbivory was rapidly acquired in tetrapods, very shortly after the permanent colonization of land. This is highly important because it means that the essential components of the terrestrial ecosystems we recognize today – as herbivore dominated – have been around and maintained since the Carboniferous period, reinventing themselves during each climate and extinction event.”
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Knowing that land-based animals became herbivores this far back helps to paint a more complete picture of how life evolved on Earth.
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