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Footage of the 'living fossil' Protoanguilla palau
It is so distinct, scientists created a new taxonomic family to describe its relationship to other eels.
The US-Palauan-Japanese team say the eel's features suggest
it has a long and independent evolutionary history stretching back 200m
years.
Details appear in the journal Proceedings of the Royal Society B.
The animal used as the basis for the new study was an
18cm-long female, collected by one of the researchers during a dive at a
35m-deep cave in the Republic of Palau.
But the scientists also mention other examples of the new eel species in their research paper.
At first there was much discussion among the researchers
about the animal's affinities. But genetic analysis confirmed that the
fish was a "true" eel - albeit a primitive one.
"In some features it is more primitive than recent eels, and
in others, even more primitive than the oldest known fossil eels,
suggesting that it represents a 'living fossil' without a known fossil
record," write the scientists.
In order to classify the new animal, the researchers had to
create a new family, genus and species, bestowing on the animal the
latin name Protoanguilla palau.
The team - including Masaki Miya from Chiba's Natural History
Museum in Japan, Jiro Sakaue from the Southern Marine Laboratory in
Palau and G David Johnson from the Smithsonian Institute in Washington
DC - drew up a family tree of different eels, showing the relationships
between them.
This allowed them to estimate when the ancestors of P. palau split away from other types of eel.
Their results suggest this new family has been evolving
independently for the last 200m years, placing their origins in the
early Mesozoic era, when dinosaurs were beginning their domination of
the planet.
The researchers say the Protoanguilla lineage must
have once been more widely distributed, because the undersea ridge where
its cave home is located is between 60 and 70 million years old.
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