Rebel Coelacanth Discovery Forces Rethink On Their Evolution
May 3, 2012

Rebel Coelacanth Discovery Forces Rethink On Their Evolution

Canadian researchers have discovered a new species of Triassic coelacanth, a fish presumed extinct until a population was found off the coast of Africa in the 1930s, while digging through a trove of museum fossils, reports Jennifer Viegas for Discovery News.

The coelacanth (pronounced SEE-la-kanth) is a primitive, slow-moving fish that is often referred to as a living fossil because it has existed largely unchanged for more than 300 million years. But the new discovery, dubbed Rebellatrix, is bizarre compared to other coelacanth discoveries, either living or extinct, according to Andrew Wendruff, a University of Alberta biologist.

Wendruff told Discovery news that the coelacanth measured more than three feet long and resembled a tuna, because of its fork-like tail.

“Since the tail of a fish is used for locomotion, much can be deduced about the type of locomotion as well as its lifestyle,” Wendruff explained. “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.”

Unlike this speed demon, most coelacanths found in the fossil record have broad, flexible tails, added coauthor Mark Wilson, also from the University of Alberta. “Those coelacanths were slow moving and usually lay in wait for their prey. Rebellatrix was able to search actively for the fishes that it preyed upon and catch them at high speed,” he explained.

Wendruff said the fork-tailed coelacanth was an ℠off-shoot´ lineage that lived 240 million years ago (mya). It falls between the earliest known coelacanth fossils of 410 mya and the latest fossils from about 75 mya.

Wendruff and Wilson, publishing their finds in this month´s issue of the Journal of Vertebrate Paleontology, surmise that Rebellatrix came along after the end-Permian mass extinction 250 mya, and event that wiped out nearly 90 percent of all marine life. Rebellatrix filled a previously unoccupied predator niche, but it didn´t fare well, they report.

“Rebellatrix was likely a spectacular failure in the evolution of cruising predation,” said Wendruff. “Clearly some other fish groups with forked-tails must have outperformed this coelacanth as it does not appear later in the fossil record.”

The fossils of this coelacanth were collected on the rocky slopes of Wapiti Lake Provincial Park in British Columbia in the 1950s, the 1980s, and then again in 2006. This area was once the western coast of Pangaea at the time Rebellatrix lived. The specimens were stored at Royal Tyrtell Museum in Alberta and the Peace Region Paleontology Research Center in British Columbia, Canada.

Wendruff said he didn´t believe what he was seeing when he first examined the fossils in 2009. It was “only when I found a second, third, and fourth ... that I realized we had something real and something significant.”

Through fossil analysis, the team thinks they have gotten the unusual shape down to two possibilities. It could be that the fossil record for coelacanths is vastly undiscovered and there are other fish out there like this one,  or it is just that this specimen represents a bizarre adaptation to life following the end-Permian mass extinction, allowing coelacanths to evolve a vacant niche unoccupied by other predatory fish.

“Rebellatrix, most importantly, 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,” Wendruff said. “Rebellatrix is dramatically different from any coelacanth previously known, and thus had undergone significant evolutionary change in its ancestry.”

While the fork-like tail gives it an uncanny resemblance to tuna and/or sharks, it shares no lineage with either fish. The researchers think the similarities are examples of convergent evolution, when nature recycles ideas, body forms and structures in response to the needs of a species, such as those driven by environmental conditions.

“This is an amazing discovery which overturns the age old image of coelacanths as slow moving fishes and shows the resilience of the group to come back in true fighting form after surviving the world´s most devastating mass extinction event,” said John Long, a fossil fish expert at the National History Museum of Los Angeles County. In general, the discovery “shows how plastic and flexible evolution can be.”

It really shakes things up “that coelacanths can suddenly deviate what they´ve been doing for 200 million years and occupy a lifestyle that´s radically different from other coelacanths,” he said.

“Modern coelacanths are very rare, do not survive in captivity, and are endangered where they live,” Wendruff said.

Wendruff and Wilson made special mention in their paper of three families -- the Byrens, Helms and Walkeleys -- and the directors of the Tumbler Ridge-based Peace Region Paleontology Research Center for their roles in the 2006 discovery of the landmark fossil near Wapiti Lake Provincial Park. And the research center´s professional paleontologists, Richard McCrea and Lisa Buckley, were hailed for having “made it their goal to preserve British Columbia's natural history.”