Some 300 million years ago, as the swampy jungle that covered much of West Virginia, Ohio and Pennsylvania was drying out, more animals started to emerge from the water. Amongst these newly terrestrial creatures is the earliest known herbivore in the vertebrate fossil record that both lived and reproduced on land.
Specimens of Melanedaphodon were unearthed at a defunct coal mine in Linton, Ohio back in 2008 – though it took researchers more than a decade to determine that the discovery was of a previously unknown species.
In a paper that came out last week in the journal Scientific Reports, researchers at Carnegie Museum of Natural History, the Smithsonian’s National Museum of Natural History and Harvard University’s Museum of Comparative Zoology assert that Melanedaphodon’s teeth were designed to eat plants. The herbivore had teeth along the top of its jaws and on the roof of its mouth, used for grinding plants in small pieces.
“One of the difficult things that these animals faced when they began eating plants is that plant cells are really hard to break down and it's hard to get nutrients out of plants,” said Carnegie Museum paleontologist Amy Henrici, adding that Melanedaphodon also likely ate insects and perhaps mollusks.
Back when Melanedaphodon roamed the dense forests that become Appalachian coal mines, most animals were carnivorous. The discovery of the herbivores helps researchers understand how quickly, geologically speaking, animals can adapt to environmental changes and begin eating plants, says James Lamsdell, a paleobiologist at West Virginia University.
“It is possible that the climatic changes were in part driving the adaptation toward a herbivorous diet as ecosystems changed from perennial swamps to seasonally wet environments,” said Lamsdell. “I would not be surprised if future discoveries revealed a number of the other herbivore groups were beginning to make the transition at around the same time.”
Ancient cousins
Melanedaphodon belongs to an extinct branch of synapsids, a group that includes all mammals and their ancestors. Researchers believe it’s closely related to Edaphosaurus, another long-gone synapsid, and therefore it probably bore a resemblance to this lizard-like creature.
“These animals have a big sail on their back, a small head, and a not particularly long tail,” said Henrici of the Carnegie Museum. “The bones that supported this sail, it was a long spine, and they had lateral bones sticking out from them … like little bumps.”
In contrast to amphibians, which lay eggs in water that hatch into tadpoles, Melanedaphodon’s reproduction was probably more reptilian in that it laid eggs on land. Young Melanedaphodons would emerge as miniature versions of the adult animal.
Melanedaphodon's descendants were probably munching on plants until about 273 million years ago, when climate change caused a mass extinction event. The environment became extremely hot, which prompted a major restructuring of terrestrial ecosystems. The majority of animals were unable to adapt, becoming evolutionary dead-ends.
