NATIONAL MUSEUM OF NATURAL HISTORY
Smithsonian Scientists Discover One of the Earliest Mammal Ancestors That Ate Its Veggies
The new finding pushes the first signs of tetrapod herbivory back millions of years
While plants first colonized land 470 million years ago, there haven’t always been animals able to eat them. Being a herbivore requires specialized traits like durable teeth to break down tough plant material and a large gut housing microbes capable of digesting cellulose. As a result, researchers have long thought that large animals did not start chowing down on greens until the early Permian period around 300 million years ago.
But the discovery of a new fossil critter may push this dietary revolution back millions of years. In a study published today in the journal Scientific Reports, Smithsonian paleontologists Arjan Mann and Hans Sues named a new species of ancient reptile-like mammal ancestor that had chompers reminiscent of living lizards like blue-tongued skinks who devour everything from fruits and veggies to insects.
“The similar tooth morphology present in this fossil animal may indicate the earliest inklings of herbivory,” said Mann, a Peter Buck Postdoctoral Fellow at the National Museum of Natural History and the lead author of the new study. “The adaptation of herbivory is now much earlier than previously recognized.”
These fossils hail from the site of a now-defunct coal mine near the eastern Ohio town of Linton. During the Late Carboniferous period, this area was a balmy stretch of wetlands whose waters contained coelacanths, spiny freshwater sharks and an abundance of amphibians. One of the stranger inhabitants was Colosteus, a large amphibian with fangs and reduced limbs that ruled these primeval swamps like a crocodile. According to Sues, these communities were also home to the earliest reptiles and the earliest forerunners of mammals.
307 million years ago, a meandering river changed course here, leaving an isolated riverbed called an oxbow lake in its wake. Eventually plant material from the surrounding swamp built up in the stagnant water and decomposed into peat. The decomposition process siphoned oxygen from the surrounding water, dooming the bog’s inhabitants. The lack of oxygen also kept scavengers at bay, ensuring the fish, amphibians and whatever else washed in was peacefully interred in the peat.
Over time, heat and pressure transformed the peat into slabs of cannel coal, a type of coal that was used to create kerosene during the nineteenth century. Between 1855 and 1921, miners extracted cannel coal out of the local Diamond Coal Mine. Almost immediately they started discovering the well-preserved remains of ancient fish and amphibians etched into the coal’s waxy, black surface.
“These fossils are basically negative impressions in the coal,” Mann said. Paleontologists have been studying these imprints for more than a century in order to understand this cache of Carboniferous creatures. Recent technological advancements like CT scans even allow researchers to digitally recreate the flattened fossils in three dimensions.
Most local fossils preserve aquatic inhabitants of these ancient bogs like amphibians and fish. But the remains of terrestrial animals also washed into these swamps. Their fossils turn up from time to time.
Parts of the skulls of two such creatures were entombed in two blocks of cannel coal now housed in the Carnegie Museum of Natural History’s collection in Pittsburgh. Together, these slabs contained jaws studded with teeth that ended in rounded, blunt points. According to Mann, who first came across the fossils in 2019 while wrapping up his PhD at Carleton University, the shape of these teeth was very odd for this type of animal at the time.
He never forgot about those strange teeth. During the pandemic, he finally had a chance to examine them in depth when he was back home in Toronto. “I decided to get off my butt and did most of the anatomical work as a pandemic project,” Mann said. To peer inside the mouth of this ancient animal, researchers had previously used a CT scanner to digitally recreate the animal’s jaws. Using these scans, Mann was able to create accurate 3D models of the original fossils, allowing him to analyze the animal’s dentition without having to travel to Pittsburgh.
In the new paper, Mann and Sues worked with paleontologists at the Carnegie Museum and Harvard University to describe the ancient animal. They christened the creature Melanedaphodon hovaneci. The genus is a mashup of the Greek word “melanos,” which means black—referring to the fossil’s dark color—and the words for “pavement” (edaphon) and “tooth” (odon), which refer to the animal’s dense clusters of teeth. The species name refers to George Hovanec, a Carnegie Museum donor who helped fund the team’s use of CT scanners to analyze the fossils. Holvanec recently passed away, and Mann and his coauthors hope the new fossil will honor his memory.The animal was a close relative of Edaphosaurus, a reptile-like mammal ancestor called a synapsid who lived during the early Permian. The alligator-sized, sail-backed Edaphosaurus was among Earth’s earliest large herbivores. It used its thick tooth plates to grind down tough plants and had a wide ribcage that housed a substantial gut to digest its leafy meals.
Melanedaphodon’s teeth, which end in bulbous points, are unique. But they do possess some similarities to the chompers of both Edaphosaurus and several living lizards that eat plants as part of their diets. These include large skinks and tegus, a group of stout lizards native to South America that devour everything from fruits and eggs to rodents and table scraps. “Those animals will eat insects if you put them in there, but will also eat fruit, vegetables and all sorts of things,” Mann said. He thinks Melanedaphodon had similarly diverse tastes. “It probably ate a mix of plant material and the occasional insect that was in its way.”
The researchers concluded that Melanedaphodon is the oldest known amniote (the animal group that includes all reptiles, birds and mammals) to subsist on a diet that included a healthy portion of low-fiber plant byproducts like seeds and bark. “Not only are we presenting a new type of herbivory present in the early fossil record, but the earliest record of such low-fiber feeding,” Mann said.
Melanedaphodon lived during a dynamic era in Earth’s history. Not long after the ancient inhabitants of Linton, Ohio, were buried inside the bog, the vast coal rainforests that dominated the Carboniferous began giving way to drier environments, sparking an extinction event. When the Permian period began around 299 million years ago, true herbivores like Edaphosaurus had become major components of terrestrial ecosystems for the first time.
But it appears that a few adventurous eaters like Melanedaphodon were already munching on greens long before herbivory went mainstream.
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