ONE of the most puzzling phases in the evolution of life is giving up its secrets. Two strange fossil types are helping palaeontologists understand the weird inhabitants of the Ediacaran period.
“We are at a watershed,” says Ediacaran expert Guy Narbonne of Queens University in Kingston, Ontario, Canada. The Ediacaran, which began 635 million years ago after a global freeze christened “Snowball Earth”, was only added to the geological timescale last year. It bridges the evolutionary chasm between the 2.5-billion-year reign of single-celled organisms and the “Cambrian explosion” of abundant animal fossils 542 million years ago.
Excavations of fossil beds, 560 to 550 million years old, south of the original Ediacara fossil beds in South Australia have uncovered enigmatic patterns that spread across the surface in different sizes and shapes: “baggy” beds look like collapsed plastic bags; “groovy” beds look like ridges on the sea floor; and “ropy” beds with filaments radiating from a point. Mary Droser of the University of California, Riverside, calls them “textured organic surfaces”. She announced the finds last month in Canada at the North American Paleontology Convention in Halifax, Nova Scotia.
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Also new and puzzling are the mysterious branching networks of hollow tubes in the Dengying fossil beds of southern China and described by Shuhai Xiao of the Virginia Polytechnic Institute and State University (Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.0502176102).
The team believes these lived lying on the seabed. They did not find any overlapping or folded sets of tubes, which you would expect if upright fronds had fallen over before fossilisation. Nor did they find anatomical structures for anchoring them to the seabed. The branching tubes, 551 to 542 million years old, were probably hollow and open at the ends.
