Once thought to be extinct, the lobe-finned fish known as coelacanths appeared 400 million years ago and still swim Earth’s oceans today. Their longevity and seeming resistance to change have earned them reputations as “living fossils.” A new coelacanth species, dubbed Rebellatrix because it defies traditional perceptions, might change our understanding of these marine creatures’ long history.

Tens of millions of years ago, ancient fish up to 6 feet long, outfitted with long fins and armor-like scales, lived in underwater caves off the supercontinent Pangaea and, later, in the Indian Ocean. Known as coelacanths (pronounced SEE-la-kanths), these marine creatures vanished with the dinosaurs at the end of the Cretaceous—or so scientists thought until 1938. That year, a young South African museum curator named Marjorie Courtenay-Latimer spotted an enormous, iridescent fish with strikingly primitive features, buried under sharks and rays aboard a local trawler. She convinced a taxi driver to haul it back to her museum, where she sketched the remarkable specimen while trying desperately to preserve it.

When the chemist and self-taught ichthyologist James Smith first glimpsed Courtenay-Latimer’s sketch, he immediately realized that coelacanths—then known to science only through fossils—had either returned from the dead or never gone extinct. Before long, experts and the press were hailing the South African fish as the “most important zoological find of the century” and a “living dinosaur.” Fourteen years later, an obsessive hunt by Smith and his wife finally turned up a second modern coelacanth specimen, and dozens more have surfaced over the years. Scientists determined that, rather than dying out 65 million years ago, coelacanths lurked under the depths and the radar, remaining largely unchanged over time. Today the fish are endangered and extremely rare.

Decades after Courtenay-Latimer’s landmark discovery, a study published May 2 in the Journal of Vertebrate Paleontology opens a new chapter in coelacanths’ long and enigmatic history. Researchers from the University of Alberta in Canada have described a new species of coelacanth, dubbed Rebellatrix, which turns the standard definition of these famous “living fossils” on its head. The extinct creature also overturns the idea that coelacanths’ bodies and lifestyle barely evolved after the animals first appeared 400 million years ago, the researchers said. “Rebellatrix means ‘rebel coelacanth,’ so named because this new coelacanth goes against the norm for coelacanths,” said lead author Andrew Wendruff. “It does things scientists thought coelacanths could not do.”

A Rebellatrix specimen from the Royal Tyrrell Museum of Paleontology, showing its stiff, forked tail. (Credit: Andrew Wendruff)

Like their modern descendants, most fossil coelacanths had broad, flexible tails, moved slowly and lay in wait for their prey, said Mark Wilson, co-author of the study. They relied on quick but short-lived bursts of speed—a technique known as lunging—while hunting smaller fish, Wendruff explained. By contrast, Rebellatrix boasted a forked, stiffened tail similar to that of a tuna or barracuda, a feature that appears many times in disparate corners of the fossil record. “Since the tail of a fish is used for locomotion, much can be deduced about the type of locomotion as well as its lifestyle,” said Wendruff. “Fish with forked tails are able to achieve higher speeds and sustain them over a greater period of time. The forked tail of Rebellatrix indicated that it was a fast-moving, aggressive predator.”

Rebellatrix first appeared after the extinction event that wiped out 90 percent of marine life at the end of the Permian period, roughly 250 million years ago. It could have evolved its unique anatomy to fill a niche left vacant by predatory fish species that didn’t survive Earth’s most severe mass die-out, the researchers hypothesized. The strategy ultimately failed, however, Wendruff explained. “While other fork-tailed fishes appear later in the fossil record, Rebellatrix and its descendants are noticeably absent,” he said. “This leads us to believe that Rebellatrix was a dead end in the evolution of cruising predation.”

Whatever the reason for its atypical features, Rebellatrix shows that coelacanths weren’t stubbornly frozen in time from their earliest history until today, according to the study. “The new body form, particularly the tail, was most surprising because it shatters the commonly held notion that coelacanths were an evolutionarily stagnant group in that their body shape and lifestyle changed little since the origin of the group,” said Wendruff. “Rebellatrix is dramatically different from any coelacanth previously known, and thus had undergone significant evolutionary change in its ancestry.”

The researchers described four Rebellatrix fossils collected within the vicinity of Wapiti Lake Provincial Park in British Columbia. Some 240 million years ago, this area was located off the western coast of Pangaea, Wendruff said. The first fossil was unearthed in the 1950s, and the most recent was found in 2007. Rebellatrix’s discovery comes on the heels of another coelacanth revelation: Chinese scientists announced two weeks ago that a coelacanth skull dates back 409 million years, suggesting the ancient creatures could be 17 million years older than previously thought.