Pouncing lions, fish-swallowing seals, and even your bone-chewing family dog can all trace their roots back to a small, tree-dwelling ancestor. Bones unearthed from a 55-million-year-old fossil trove have revealed a diminutive creature at or near the root of today's formidable lineage of carnivorous mammals.
Paleontologist Floréal Solé of the Royal Belgian Institute of Natural Sciences and a team of colleagues recently described more than 250 new teeth, jaw, and ankle bone specimens of Dormaalocyon latouri, named for the Belgian locality of Dormaal where the fossil was first found in a site long famed for early Eocene epoch remains.
Fossilized jaw bones and teeth, including baby teeth, provide valuable evidence of the ancient animal's taste for flesh. According to Solé, Dormaalocyon is the most primitive known member of the carnivoraforms group. That group is represented by today's 280-plus species of living carnivorous mammals, the order Carnivora, which includes lions, seals, bears, cats, dogs, and others—all of which count this creature as their ancestor.
Three other carnivorous mammal families (Oxyaenidae, Hyaenodontidae, and Viverravidae) also existed back in the Paleogene but have since died out, Solé said. Chronologically, Dormaalocyon is not the oldest carnivoraform ever found: Another arboreal creature called Uintacyon is one million years older, although it is thought to be farther from the root of the group.
A Cross Between a Squirrel and a Small Cougar
Dormaalocyon, which may have looked a bit like a cross between a squirrel and a small cougar, shows oral features with important adaptations to a meaty diet. The one- to two-pound (half- to one-kilogram) mammal likely consumed insects and other animals smaller than itself. (Related: "Newly Discovered Carnivore Looks Like Teddy Bear.")
Dormaalocyon lived during the Paleocene-Eocene boundary epoch, and fossils from this period have been extremely hard to come by, said Gregg Gunnell, director of the Division of Fossil Primates at Duke University's Lemur Center, who was unaffiliated with the research.
"It's really a matter of just finding the right rocks, and there aren't that many," he explained. "If you don't have that little slice of time preserved in the right rocks, from maybe 55.8 to 56 million years ago, then you are out of luck. So this animal provides a limited sort of window in time at the Paleocene-Eocene boundary, and that lasted for only maybe a couple of hundred thousand years."
Dormaal is one of the very few places in Europe that fossils have been found from the period, Gunnell added. In North America such fossils have been found in just a couple of Wyoming locations, and in Asia they've been found in just a single spot in China, he said. (Related: "Fossil Reveals Long-Lived Mammal Group's Secret.") The scant evidence makes it impossible to determine if the carnivores arose in Asia and spread westward, or had a different geographical origin.
"Despite all the looking, that's all we've ever found," said Gunnell. "It's like trying to put together a 500-piece puzzle when you only have three pieces and trying to see what the picture is going to look like. So this fossil is quite rare, a teeny glimpse on a world that we don't know much about."
Hot, Forested Earth
The Paleocene-Eocene Thermal Maximum (PETM) was a period of evolution, extreme global warming, and low sea levels that opened a land connection between Europe, North America, and Asia. That land bridge allowed mammals, primates, rodents, and other vertebrates to spread during this time. (Related: "World Without Ice.") The period ended rather abruptly during the early Eocene, leaving species to further evolve endemically in their continental locations when waters rose.
"This fossil is from about the same time that we're starting to see real primates showing up for the first time, so it appears to be a part of that radiation of modern animals that shows up at the Paleocene-Eocene boundary," Gunnell said.
Dense forests predominated across the Northern Hemisphere, perhaps prompting Dormaalcyon's adaptation to life in the trees as evidenced by its ankle bones.
"Being arboreal, it probably fits in nicely with the arboreal primates that are showing up at that same time, part of a very early Eocene fauna that spread quickly across the northern continents," Gunnell explained.
The Paleocene began after the Cretaceous-Tertiary mass extinction about 65 million years ago and featured a key period of evolutionary expansion when mammals and birds spread across the globe to occupy ecological niches vacated by recently vanished dinosaurs and larger reptiles. It lasted until about 55 million years ago and was followed by the Eocene, which lasted roughly from 55 million to 33.9 million years ago. (Related: "Dino-era Mammal the 'Jurassic Mother' of Us All?")
"Because of the diversity of the carnivoraforms during the earliest part of the Eocene, we think that they diversified during the late Paleocene," Solé said, noting that his group is also at work in a new locality in Europe where other late Paleocene species may be found. It's his hope that future finds from the period can help paleontologists determine whether the placental mammals adopted a carnivorous lifestyle just once, or several times within the different and now extinct groups.
"This question is important for understanding the evolution of mammals after the disappearance of the majority of the dinosaurs," said Solé.
The study was originally published in the Journal of Vertebrate Paleontology.