Beardogs were neither bears nor dogs. But they might have been the forebears of both. Scientists at Chicago’s Field Museum say two specimens of the Chihuahua-sized animals have just rearranged the branches of the carnivore family tree. A report on the new classifications was published today in the journal Royal Society Open Science.
The beardogs, also known as the amphicyonids, were a family of sturdy, four-footed carnivores that emerged around 40 million years ago. They were a diverse group, ranging widely in size and shape. Some were huge and bearlike; others, like the Field Museum’s fossils, would have maxed out at about 11 pounds.
Shortly after joining the Field Museum, paleontologist Susumu Tomiya decided to take a stroll through the museum’s collections. He was in a room of type specimens—that is, specimens used as perfect examples of their species—when he saw something strange: a carnivore with funny teeth.
“There were beautiful jaws of a small carnivore,” he said in a statement, “but the genus the specimen had been assigned to didn’t seem to fit some of the features on the teeth. It made me suspect that it belonged to a very different group of carnivores.”
The teeth of pure carnivores are sharp so their owners can puncture, bite, tear, and chew tough flesh. But some of the teeth in front of Tomiya had flattened areas, as though they had been used for crushing and grinding. The beardog to whom they belonged, a species called Miacis australis, was supposed to have been on an all-meat diet. Something wasn’t right.
Tomiya kept looking. In the collections at the University of Texas, he found another weird specimen: partial remains from a related beardog called Miacis cognitus, taken from the same rock formation as M. australis’s remains. The second specimen’s lower jaw was missing, but the back of its head was intact.
Tomiya and his coauthor Jack Tseng of the University of Buffalo then used a computed tomography (CT) scanner to create 3D visualizations of the inside of M. cognitus’s skull. They were especially interested in the area around the inner ear, which can often be used to determine relationships between carnivore species.
They found that the two species were closely related and near-contemporaries that likely lived around 37 or 38 million years ago. These were early, early creatures indeed—so far back in the tree of life that they could be called the ancestors of both bears and dogs. And seals. And weasels.
Both specimens had also been classified wrong. Based on the dental and CT evidence, Tomiya and Tseng reassigned M. australis to the genus Gustafsonia and M. cognitus to the genus Angelarctocyon.
The two beardogs’ reassignment has significance beyond their species, Tomiya said: “Studying how the diversity of beardogs waxed and waned over time could tell us about larger patterns in carnivore evolution.”
And while the two specimens are long dead and gone, they still have a lot to tell us about the history of our planet.
“Gustafsonia and Angelarctocyon lived at a time when North America was transitioning from a subtropical climate to a cooler, drier climate,” Tomiya said. “There were big changes happening in the landscape, forests were probably opening up, and the fossil assemblages including these beardogs can tell us about what kinds of animals did well in that environmental context.”
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