CAMBRIDGE, Mass. -- Researchers from the Massachusetts Institute of Technology, the Paleontological Institute of Moscow and the California Institute of Technology report in the May 5 issue of Science that they have reliably pinpointed the age of some of the world's first complex animals.
The White Sea of Russia's menagerie of Ediacaran fauna -- soft-bodied, blobby creatures that look like jellyfish and fronds -- is one of the most diverse fossil assemblages of its kind, but it has never before been assigned an accurate age to secure it to the geological and paleontological record.
Mark W. Martin, postdoctoral research associate, and Samuel A. Bowring, professor of Earth, Atmospheric and Planetary Sciences at MIT, and their colleagues used isotope dating of the mineral zircon found in volcanic ash layered with the fossil-bearing rocks to arrive at an age of 555 million years.
This new date is important because it is the oldest reliable date for tracks of organisms believed to have been made by worm-like animals. The ability of an animal to move through sediment on the sea floor implies a certain level of architectural complexity, such as the existence of a rigid body and gut.
In addition, the White Sea also contains one particular fossil known as Kimberella that is found only there and in Australia. Paleontologists believe it may be an early mollusc-like organism. This new age is a minimum for the appearance of this organism, Martin said.
A HOTBED OF FOSSILS
This new, earlier date could change how scientists view the rise of multi-cellular organisms approximately 600 million to 543 million years ago. "This new age extends the appearance of diverse multi-cellular life capable of producing tracks on the sea floor deeper in time," Martin said. "It is an important absolute time constraint that is needed to further our understanding of the evolutionary history of these unique multi-cellular organisms and their relationships to animals that evolved during the Cambrian explosion after 543 million years ago."
The White Sea area is one of the most plentiful repositories of body and trace fossils of early multi-cellular organisms preserved in the world. "While other Ediacaran fauna are found in numerous locations around the globe, they are generally not as well-preserved, lower in diversity and numbers, and not well-dated," Martin said.
One other location in Australia has similar fossil diversity and numbers of organisms. The absolute age of both the White Sea and Australia fossil assemblages was not known, though many paleontologists who have studied these fossils have suggested that they are similar in age based on the striking similarity of the fossil assemblages. Some researchers previoulsy speculated that the age of these two fossil assemblages was probably around 549 million to 543 million years, based on similar fossils of this age found in Namibia.
This work was funded by the National Science Foundation, the Russian Fund for Basic Research and the National Geographic Society.