Fossil of Rebellatrix Coelacanth Brings Light To Evolutionary Path of Coelacanths

The coelacanth is one of the oldest species of fish in the world.

The fish was thought to be extinct since the Cretaceous period, 65 million years ago. But in 1938, the first living coelacanth was caught off the coast of South Africa. That species has the scientific name, Latimeria chalumnae. It was named after its discoverer, Miss Marjorie Courtenay-Latime. Miss Courtenay-Latime was the curator of the East London Museum in East London, South Africa at the time.

Upon seeing the fish at the docks, she said, " "I picked away at the layers of slime to reveal the most beautiful fish I had ever seen," she said. "It was five foot[feet] long, a pale mauvy blue with faint flecks of whitish spots; it had an iridescent silver-blue-green sheen all over. It was covered in hard scales, and it had four limb-like fins and a strange puppy dog tail."

Evolutionary Bridge

Indonesian coelacanth and Arnaz Mehta Erdmann, at about 50 foot depth.
Photograph by Mark V. Erdmann, July 1998.

The coelacanth is closely related to the lungfishes and tetrapods. These animals form part of the chain or evolutionary bridge linking sea creatures and land animals. The fins of the coelacanth contains bones that resemble toes divided into three lobes called a trilobate fin. There is a second tail that goes along and extends past the primary tail separating the upper and lower half of the coelacanth.

The fish also has highly modified scales that are tight like armor and rough. Known as cosmoid scales, these as act as thick armor that protects the coelacanth from rocks and predators. The braincase of the fish is mostly filled with fat and only 1.5% of it is brain tissue.

The eyes of the coelacanth are extremely sensitive to light. The eyes contain a special adaptation known as a tapetum. Tapetum are also found in other animals such as cats, dogs, and dolphins. It is the tapetum that causes a cat's eyes to glow when exposed to bright light. This highly specialized eye enables the coelacanth to see as much as possible in the lightless environments of the deep sea.

They can grow up to 1.8 meters (approx. 6 feet) long.

New coelacanth find rewrites history of the ancient fish

Coelacanths, an ancient group of fishes once thought to be long extinct, made headlines in 1938 when one of their modern relatives was caught off the coast of South Africa. Now coelacanths are making another splash and University of Alberta researchers are responsible.

Lead U of A researcher Andrew Wendruff identified fossils of a coelacanth that he says are so dramatically different from previous finds, they shatter the theory that coelacanths were evolutionarily stagnant in that their body shape and life-style changed little since the origin of the group.

Wendruff says his one-metre-long, forked tailed coelacanth was an 'off-shoot' lineage that lived 240 million years ago. It falls between the earliest coelacanth fossils of 410 million years ago and the latest fossils dated about 75 million years ago, near the end of the age of dinosaurs.

Video: Finding the Coelacanth

"Our coelacanth had a forked tail, indicating it was a fast-moving, aggressive predator, which is very different from the shape and movement of all other coelacanths in the fossil record," said Wendruff.

Wendruff's research co-author, U of A Professor Emeritus Mark Wilson, describes typical coelacanths as having chunky bodies, fins of varying size and broad, flexible tails. "These fish were slow moving and probably lay in wait for their prey," said Wilson.

Wendruff's coelacanth is named Rebellatrix, which means rebel coelacanth. The researchers say Rebellatrix came along after the end-Permian mass extinction 250 million years ago, an event so lethal it wiped out 90 per cent of marine life. Rebellatrix filled a previously unoccupied predator niche, but it didn't fare well.

Rebellatrix divaricerca, gen. et sp. nov., holotype, PRPRC 2006.10.001, Lower Triassic, Sulphur Mountain Formation, British Columbia, Canada. A, photograph of holotype in right lateral view; B, close up of lateral line system of holotype; C, close up of a scale, dotted line represents scale margin;

"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 Rebellatrix described by the U of A team were found in the Rocky Mountains near Tumbler Ridge, British Columbia.

Quantum Day

03 May 2012

Fossil of Rebellatrix Coelacanth Brings Light To Evolutionary Path of Coelacanths