A bear that looked like a raccoon and had a dangerous appetite
About 30 million years ago, a primitive bear roamed around a river in what is now North Dakota. A male, he probably looked like a raccoon and might have eaten like an otter. An inspection of the curious creature’s skeleton gives details of the animal’s commandand probably painful, life and clues about the evolution of early carnivores.
Paleontologists unearthed the bear fossil in 1982. “It’s a fantastic specimen that is extremely well preserved,” said Xiaoming Wang, a vertebrate paleontologist at the Los Angeles County Natural History Museum. The skeleton includes the baculum, a penis bone found in many mammals that is rarely preserved. In an article published earlier this month in The Journal of Vertebrate Paleontology, Dr. Cheek details the creature’s facial features, from its teeth to the tips of its toes.
“This animal really tells us a lot of stories,” he said, adding that his team also found five other members of this species in nearby sediments.
Based on comparisons with living and extinct animals, Dr. Wang the creature early in the evolution of mammalian carnivores, a group that includes the dog family and feline and bear-like animals. This specimen’s relatively large molars told the scientists it belonged to the arctoids, a huge group of carnivores that includes bears, seals, skunks, raccoons, weasels and otters. The arctoids also share a common ancestor with dogs. However, this animal was not the ancestor of modern bears. “It’s a small side branch, but it’s a very important side branch,” said Dr. Cheek.
The team of dr. Wang named the animal Eoarctos vorax. Referring to the lineage’s evolutionary antiquity, “Eoarctos” combines Greek words for dawn and bear. “Vorax” means voracious, nodding to an appetite that may have gotten the best of this creature.
From snout to tail, the Eoarctos vorax was about two feet long. Many of its skeletal features resemble those of raccoons, said Dr. Cheek. With claws longer and sharper than modern dumpster divers, Eoarctos would have been adept at climbing trees and perhaps using that ability to escape predators. Although his ancestors would have lived in trees, this creature was probably terrestrial. His relatively flat feet would have enabled him to walk long distances.
In recent decades, paleontologists thought that arctoids originated in Europe. But researchers “make a strong case that these groups are, in fact, from North America,” said Blaire Van Valkenburgh, a vertebrate paleontologist at the University of California, Los Angeles, who was not part of the study.
The Eoarctos appears to be one of the earliest carnivores capable of crushing hard objects, such as bones. A dental examination revealed that the animal had broken teeth in the back of its mouth on the right side of its jaw, which had most likely become infected. Then, before he healed, he used the left side and damaged those teeth as well. “Those are the broken off roots,” said Dr. Van Valkenburgh. Some of the other individuals also lost teeth in the same way. “They must have eaten very hard things,” she said.
The team of dr. Wang suspects that Eoarctos chewed on molluscs in North Dakota’s prehistoric rivers and crushed their shells like otters do. Because of its tiny skull, only about four inches long, the bones of potential prey seem unlikely to cause the kind of damage the Eoarctos suffered, though Dr. Van Valkenburgh wondered if he might have eaten fruit with hard seeds.
Chewing such hard foods seems like a rather specialized way of eating. “That in itself is quite interesting,” said Dr. Van Valkenburgh. At the time of the dawn bear, mammals began to fill the gaps in ecosystem roles left by the demise of dinosaurs 35 million years earlier. It takes a long time for the diversity of organisms we have today to evolve, she added.
Food could ultimately be the cause of this animal. By analyzing the relatively unworn teeth of the complete Eoarctos specimen, Dr. Wang saw that this male died young, possibly due to a blood infection caused by his injuries. The double jaw injury would have been incredibly painful, Dr. Wang said, and the creature would have suffered for weeks or months.
“But for all his suffering, he certainly made a huge contribution to science,” said Dr. Cheek.