Five-million-year-old saber-toothed cat in newly discovered genus discovered in Florida

The 5-million-year-old fossils belong to the same lineage as the famous Smilodon fatalis from the La Brea Tar Pits in Los Angeles, a large, carnivorous apex predator with elongated upper canine teeth. Previous research suggested the group of saber-toothed cats known as Smilodontini originated in the Old World and then migrated to North America, but the age of the new species indicates the group likely originated in North America.

The study appeared online in the journal PLOS One on March 13.

"Smilodon first shows up on the fossil record around 2.5 million years ago, but there haven't been a lot of good intermediate forms for understanding where it came from," said study co-author Richard Hulbert Jr., vertebrate paleontology collections manager at the Florida Museum of Natural History on the UF campus. "The new species shows that the most famous saber-toothed cat, Smilodon, had a New World origin and it and its ancestors lived in the southeastern U.S. for at least 5 million years before their extinction about 11,000 years ago. Compared to what we knew about these earlier saber-toothed cats 20 or 30 years ago, we now have a much better understanding of this group."

Hulbert helped uncover fossils of the new genus and species, Rhizosmilodon fiteae, from a phosphate mine during excavations in 1990. The species was named after Barbara Fite of Lutz, Fla., who in 2011 donated one of the critical specimens used for the new description and allowed UF scientists to make casts of two other partial jaws in her collection.

The donation was a major contribution to the research because the remarkably well-preserved lower jaw contains almost pristine examples of all three chewing teeth, Hulbert said. The genus name Rhizosmilodon, meaning "root of Smilodon," implies the animal could be a missing link and direct ancestor of Smilodon, which became extinct about 11,000 years ago.

The study's lead author, Steven Wallace, an associate professor in the department of geosciences and member of the Don Sundquist Center of Excellence in Paleontology at East Tennessee State University, used comparative analysis of saber-toothed cat anatomy to help determine the animal's taxonomy. The analysis was primarily based on structure of the animal's lower jaw and teeth, smaller than the Smilodon and about the size of a modern Florida panther.

"The taxonomy of this animal was controversial because when it was first published 20 years ago, they only had one partial, somewhat-decent lower jaw, and it was missing some of the critical features," Hulbert said. "We now have more complete specimens showing it has a mixture of primitive and advanced characters, and does not match any previously named saber-toothed cat genus or species."

Originally misidentified as a member of the genus Megantereon in the early 1980s, Rhizosmilodon is instead the sister taxon to Megantereon and Smilodon, and the oldest of the group. These three cats are in the same tribe -- meaning they are more closely related than a family or subfamily -- and are often called as saber-toothed cats because of their long canine teeth, Hulbert said.

"When people think of saber-toothed cats, they think of it as just one thing, as if the famous tar pit saber-toothed cat was the only species, when in fact, it was an almost worldwide radiation of cats that lasted over 10 million years and probably had a total of about 20 valid species," Hulbert said. "Counting the newly described animal, there are now six different species of saber-toothed cats known just from Florida."

Saber-toothed cat expert Julie Meachen, an instructor at Marshall University School of Medicine in Huntington, W. Va., said the study helps settle the debate about whether the tribe arose from the Eurasia before coming to North America.

"I think that this revision was well-needed," Meachen said. "The fact that it's one of the oldest lineages is really interesting because that means that this exciting group of saber-toothed cats really is a North American tribe -- it evolved and persisted in North America."

Since 1915, more than 60 new species of reptiles, birds and mammals have been named from Central Florida phosphate mines, located southeast of Tampa and south of Lakeland. Rhizosmilodon lived in a forested coastal habitat that was also home to rhinos, tapirs, three-toed horses, peccaries, llamas and deer. Its relatively small size probably allowed it to climb trees and safely hide captured prey from large carnivores, such as packs of wolf-sized hyena-dogs and an extinct type of bear larger than the modern grizzly.