Paleodictyon: The Creature That Has Never Been Seen
In a dark, dark ocean, there is a dark, dark ridge,
And on that dark, dark ridge, there is a dark, dark burrow,
And in that dark, dark burrow there is a dark, dark tunnel,
And in that dark, dark tunnel there lives…?
Deep beneath the mid-Atlantic there lives a creature. It is a creature that has lived undisturbed and unchanged for 50 million years. It is a creature that has never been seen.
This is not the story, as you might assume, of a mythical creature. This is no Loch Ness Monster, Bunyip or Yowie. This is a creature for which fossils exist, and that has been repeatedly confirmed by photographic evidence obtained by submarines since 1976, under the leadership of Professor Peter Rona of Rutgers University, New Jersey, USA.
But the photographs and fossils show only a distinct structure, perhaps a burrow, made by the creature; the creature itself remains unknown.
The surface of the burrow is shaped like a small hexagon pockmarked with three evenly spaced rows of holes. The holes drop as vertical shafts that then connect to a network of tunnels just below the surface. What lives in these tunnels, what built them and preserved them, is a mystery.
These features match ancient fossils of an animal known as Paleodictyon nodosum, which is thought to have been an invertebrate living before the extinction of the dinosaurs. The modern burrows, therefore, are also thought to be Paleodictyon nodosum, alive and well.
But wait! If the creature has never been seen, how can you call a burrow a species?
The question is whether the structure is a burrow made by the animal, perhaps dug out to grow food or to live in, or whether the curious, honeycomb-looking underwater network is the animal, like an ancient sponge.
Are the ancient Paleodictyon fossils the traces of a home left behind by a creature long since disappeared, or the fossilized bodies of the animals themselves?
If the first option is correct, the tunnels would most likely serve as a bacterial farm. There isn’t much food on the deep sea floor, so this would be a good way to make sure that you never go hungry. But while DNA tests showed amoebae living on the surface of modern Paleodictyon, other tests rejected this theory.
“The number of bacteria inside and outside of the form were the same,” says Professor Rona. “So it doesn’t seem to be a bacterial farm.”
What about the second option?
Rona’s team looked at how the hexagonal structure grows. They found that as the diameters of the fossils expand, the number of holes increase at precisely the same rate as would be expected if Paleodictyon had been a living structure, growing outwards. They also show that the form is a clever piece of architecture, raised in the middle and forming a moat around its edge, that tames and controls the ocean currents just enough to make sure all the holes can be fed equally by the nutrients the water carries.
“The way the form grows favours the body fossil interpretation,” claims Professor Rona. “So too does the rejection of the bacterial farm idea.”
Being a body fossil rather than a trace fossil might sound disappointing — it is easy to glamourize the tale of a never-before-seen creature carving out a metropolis on the underwater boundaries of Planet Earth’s tectonic plates; and less easy to glamourize an old sponge — but such a possibility could mean something remarkable in nature.
If the Paleodictyon ‘burrow’ is the animal, Rona’s team wonder if it might be most similar to the Ediacara fauna, fossils that were found around the world in a fit of scientific discovery in the late 19th and early 20th centuries, and eventually named after the Ediacara hills in the northern Flinders Ranges of South Australia. The Ediacara represent some of the earliest known multicellular organisms, dating back to 600 million years ago. All of them have long since died out. From the deserts of Australia to South America and Europe, the Ediacara covered the planet. Could they still be alive, down there in the darkness of the Atlantic Ocean?
Plus, if Paleodictyon is the animal, not a burrow, not all of the evidence obtained makes sense. Samples from a 1993 dive, for example, were tested for protoplasm, the contents of living cells that enable all of the processes of life to continue. There was none.
Perhaps, though, it is a creature that doesn’t have any.
Paleodictyon nodosum is a living fossil that may, or may not, have ever been seen. Its true nature remains a mystery.
“We are seeking submersible time to address unanswered questions,” adds Rona, “Our pursuit of Paleodictyon continues”.
By Simon Bishop
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