The term "living fossil" was first used by Charles Darwin in his book On The Origin of Species. He used it to describe species that have survived for millions of years with little to no apparent evolution because they "inhabited a confined area, and from having thus been exposed to less severe competition."
In other words, these organisms, unlike most species, did not need to evolve to survive in their habitats. Well-known examples of living fossils include the coelacanth and the gingko biloba tree.
And now, a new living fossil has been discovered in Palau - an eel with the scientific name of Protoanguilla palau. "Protoanguila" means "first eel."
"There hasnít been anything comparable to this since the coelacanth was discovered," said Smithsonian Institution ichthyologist Dave Johnson, referring to the fish famously rediscovered in the 1930s.
There is one big difference, though. The coelacanth was known to scientists from its appearance in the fossil record. In the case of Protoanguilla palau, no fossil records of its existence have been found.
THE DISCOVERY OF P. Palau
A researcher with the Southern Marine Laboratory of Palau first discovered the eel while diving in a reef cave off the coast of Palau. He didn't recognize the species and brought a sample to the Laboratory for identification. Initially, the scientists were unsure has to whether this organism was an eel, or some other species of fish.
An expedition to obtain additional samples of the eel was made in March 2010 by a team led by Masaki Miya of the Natural History Museum and Institute in Chiba, Japan, Jiro Sakaue from the Southern Marine Laboratory in Palau and G David Johnson from the Smithsonian Institute in Washington DC.
To solve the puzzle of this previously unknown species' heritage, researchers compared the creature's anatomic characteristics to those of more than 800 species of modern eels as well as to all known ancient eel fossils.
Eventually, scientists concluded that the new find showed physical traits that were present only in the fossil records of ancient eels, dating back 100 million years. Additionally, the new eel was found to have certain features never before seen in other eel species.
The anatomical comparisons were followed up by an analysis of P. palau's mitochondrial DNA, Through these tests the researchers determined that the eels date back 200 million years. That's 100 million years earlier than the oldest known eel fossils.
WHAT'S NEXT FOR P. PALAU?
The researchers' work is not yet done on this species. For example - they must now make a study of the life history of the eel. What features may have helped it survive so long relatively unchanged? How does it reproduce? In what habitats can it be found?
At present, Protoanguilla palau has been found only in the once location near Palau. Researchers believe, however, that the eel must have had been much more common in the past because the cave in which they were found is only 60 - 70 years old - indicating a wider distribution must have existed. The scientists think that the eel may live in other remote habitats, as yet undiscovered.
And - perhaps most importantly of all - how can the species be protected? Masaki Miya, one of the discoverers of the eel, has talked about his concern that the species will not become endangered by all this attention. Accordint to Miya, "Professional as well as amateur divers are always curious about animals and those working for the aquarium trade are notorious for trying to keep every animal in their tanks... We should promote a campaign for preserving animals to the Palau government shortly after the (study's) publication."
Fish Caught in Time: The Search for the Coelacanth
On Methuselah's Trail: Living Fossils and the Great Extinctions