A Memorial palaeobiology graduate student has discovered a new fossil species in Ediacaran-aged rocks from Newfoundland, dated to 551 million years old.
Heléna Muirhead-Hunt found the new fossils at the Inner Meadow site in Upper Island Cove, N.L., known for exceptional preservation of soft-bodied organisms without shells or bones.
“Most of the fossils on the site belong to the enigmatic Ediacara biota of proto-animals, such as the fractal-like rangeomorphs that Newfoundland is famous for,” said Ms. Muirhead-Hunt. “But when we uncovered the first specimen of our new fossil, we knew that we were onto something really special.”
The gift of discovery
When she showed the fossil to her supervisor Dr. Duncan McIlroy, he suggested that she compare it with an obscure but important group of organisms called ctenophores, the oldest of which are 20 million years younger than Ms. Muirhead-Hunt’s newly discovered fossils.
They concluded that their fossils are close relatives to a group of stem-ctenophores well known from the much younger Burgess Shale fossil site in British Columbia.
While not a large group of modern animals, ctenophores, also known as comb-jellies, are significant to biologists and palaeontologists.
Modern comb-jellies are centimetre-sized blobs of jelly with longitudinal “comb-rows” that shimmer in waves of rainbow colours when they swim. Their ancient relatives, known as the stem-ctenophores, were sedentary.
Scientists have puzzled over what might have been the earliest animal ancestor since Darwin’s time. Most of them considered sponges to be the simplest animals.
More recently, a fierce debate has developed around what came first: the sponge or the ctenophore?
“We have known about the presence of the jellyfish relatives Haootia and Mamsetia and the sponge-like Lydonia in the Ediacaran rocks of Newfoundland for a decade or more,” said Dr. McIlroy, “and while we have been hoping to find other animals, I never even considered that we might find a ctenophore.”
Introducing Edrathina obditchia
The new fossil, published in Frontiers in Ecology and Evolution, has been named Edrathina obditchia.
Ms. Muirhead-Hunt says she wanted the name to reflect that they think the fossil is a relative of the comb-jellies.
“Since we know the Beothuk word for comb is “Edrathin” and “Obditch” is beast, combining them into the new name seemed like a fitting tribute to the culturally extinct Beothuk people of Newfoundland,” she said.
Significant to science
Beyond being the first fossil of its kind, an Ediacaran stem-ctenophore will add palaeontological fuel to the already fiery debate of the oldest animal ancestor.
Until recently, the biologically simple sponges seemed like intuitive candidates for the oldest animal ancestor because modern sponges have a very simple body plan with no muscles and no nervous system.
However, upon discovering that sponges have unexpressed genetic coding for those animal characteristics, the possibility that sponges might not be as primitive as they appear has gained ground.
The alternative ctenophore-first hypothesis posits that comb-jellies might have branched from the animal tree of life before sponges evolved, with most of the debate centred on genetics.
A missing piece of evidence in the ctenophore-first hypothesis was the lack of Ediacaran ctenophore fossils.
“We think we might have filled that 20-million-year gap in the ctenophore fossil record,” said Ms. Muirhead-Hunt.
Dr. McIlroy says the discovery is the “most amazing” fossil site he has ever worked on.
“And there are more palaeontological marvels to share in the very near future,” he said.
The fossils remain in situ in accordance with provincial law and on privately owned land. Plaster copies are being made for The Rooms Provincial Museum collection.
