Euphanerops, the fish with two anal fins, offers surprising evolutionary clues
Here are some things you should know about Euphanerops:
Euphanerops was a jawless fish.
Euphanerops swam the ancient seas 370 million years ago.
Euphanerops had a fin on each side of its anus.
It means Euphanerops was one of the earliest vertebrates with paired appendages, the type of feature that gave rise to human arms and legs.
But the paired fins are in a very odd place, according to Robert Sansom, the lead author on the study.
"It's not clear why the fins are positioned so far back on the fish, or what advantage they might have provided. However, they do show that our early vertebrate ancestors tried out lots of different body plans before settling on two arms and two legs. If they hadn't then our bodies would have looked very different!" said a statement quoting Sansom, who works at the University of Manchester's Life Sciences Department.
He made the paired-butt-fins discovery after a study of Euphanerops fossils in Quebec. Analysis, including 3D scans of the fossils, showed the fish had no pectoral or pelvic fins but a surprising two anal fins.
Jawed fish, modern or ancient, have a single anal fin that helps provide stability when swimming.
But the jawless Euphanerops' paired appendage is an intriguing one, according to the Sansom. It means that at this point in biological history there was a high degree of, well, evolutionary weirdness -- that limbs, a complicated feature, did not develop in a smooth, uncomplicated line.
"The age of Euphanerops is important as it dates from the time of a deep evolutionary split between jawed and jawless fish (to) the two main divisions of vertebrates alive today. As such, it represents an important stage in the evolution of paired appendages."
Kate Allen is the Star's science and technology reporter. Find her on Twitter at @katecallen