Is Paleodictyon a Living Fossil?
Tuesday, 25. August 2009, 18:10:42
A team of a dozen scientists now report new in situ observations and laboratory studies of specimens of a small (diameter 2.4–7.5 cm) strikingly hexagonal form originally described from sedimented steps in a wall of the axial valley of the Mid-Atlantic Ridge (water depth 3430–3575 m) near 26°N, 45°W that appears to be identical to the iconic form Paleodictyon nodosum described as a trace fossil from Eocene flysch deposits at sites in Europe and Wales.
(This photo of Paleodictyon is from the Benkovac Stone Unit. The Late Eocene Benkovac Stone Member of the Promina Formation of northern Dalmatia, Croatia, is a thinly bedded succession of alternating carbonate sandstones and calcareous mudstones, ca. 40 m thick, exposed as a narrow, SE-trending outcrop belt near the town of Benkovac. The Eocene was an epoch from ca. 56 - 34 million years ago.)
The team has gathered enough evidence to prove that the organism represents one of the world’s oldest living fossils, perhaps the oldest. The ancestors of the creature, Paleodictyon nodosum, go back to the dawn of complex life. And the creature itself, known from fossils, was once thought to have gone extinct some 50 million years ago.
So far it has not been possible to capture one of the creatures alive. It thrives in restricted areas of Atlantic seabed. Its only visible feature consists of tiny holes arranged in six-sided pattern. Until the real creature has been caught the scientists still vigorously debate what it is. The main question is whether the hexagonal patterns are burrows or body parts, vacant residences or animal remains.
The new paper seeks no consensus on the question of whether the holes and subsurface networks represent burrows or body parts. Dr. Seilacher, who backs the burrow idea, sees the tunnels as a kind of farm where an unknown type of worm or other organism raises micro-organisms to eat, while Dr. Rona sees the holes as body parts, perhaps from a type of compressed sponge. The lack of biological clues, he said in an interview, may arise because microbial predators eat the remains after the creatures die.
Reference:
Rona et al.
Paleodictyon nodosum: A living fossil on the deep-sea floor
doi:10.1016/j.dsr2.2009.05.015
(Article in Press)
(This photo of Paleodictyon is from the Benkovac Stone Unit. The Late Eocene Benkovac Stone Member of the Promina Formation of northern Dalmatia, Croatia, is a thinly bedded succession of alternating carbonate sandstones and calcareous mudstones, ca. 40 m thick, exposed as a narrow, SE-trending outcrop belt near the town of Benkovac. The Eocene was an epoch from ca. 56 - 34 million years ago.)
The team has gathered enough evidence to prove that the organism represents one of the world’s oldest living fossils, perhaps the oldest. The ancestors of the creature, Paleodictyon nodosum, go back to the dawn of complex life. And the creature itself, known from fossils, was once thought to have gone extinct some 50 million years ago.
So far it has not been possible to capture one of the creatures alive. It thrives in restricted areas of Atlantic seabed. Its only visible feature consists of tiny holes arranged in six-sided pattern. Until the real creature has been caught the scientists still vigorously debate what it is. The main question is whether the hexagonal patterns are burrows or body parts, vacant residences or animal remains.
The new paper seeks no consensus on the question of whether the holes and subsurface networks represent burrows or body parts. Dr. Seilacher, who backs the burrow idea, sees the tunnels as a kind of farm where an unknown type of worm or other organism raises micro-organisms to eat, while Dr. Rona sees the holes as body parts, perhaps from a type of compressed sponge. The lack of biological clues, he said in an interview, may arise because microbial predators eat the remains after the creatures die.
Reference:
Rona et al.
Paleodictyon nodosum: A living fossil on the deep-sea floor
doi:10.1016/j.dsr2.2009.05.015
(Article in Press)
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http://www.nytimes.com/2009/08/25/science/25fossil.html
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http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VGC-4WD1BWS-4&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=989443494&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=900183d12bc1802d8470f85e1b961b5b
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http://my.opera.com/nielsol/blog/2008/11/03/tracefossils-paleodictyon
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