University of Bristol

Recent discoveries

Recently two extroadinary groups of fossils have been discovered hinting at a long Precambrian history for metazoan life.

One billion year old trace fossils from India

trace fossil Adolf Seilacher and his team (references Seilacher et al. 1998) claim to have discovered fossilized worm burrows from rocks over one billion years old. The traces are attributed to undermat miners, animals which excavate burrows under microbial mats growing over the surface of sediments. The markings are described as too irregular to be syneresis cracks, too delineated to be wrinkles and too large (5mm diameter) to be attributed to protists or fungi. This along with other features has convinced the team that the traces have a metazoan origin. Other researchers are sceptical, inorganically produced bedding features have often before been misidentified as trace fossils, the age of these structures means that many palaeontologists will require a lot of convincing.

The potential Precambrian trace fossil. Science, Seilacher et al. 1998, 282, p81.

Animal embryos from the Neoproterozoic

A spectacular new fossil deposit has been recently unearthed in the Doushantuo formation of Southern China. Preserved in 570 million year old phosphorites are algae and tiny spheres believed to be embryos in early cleavage states (references Xiao et al. 1998)

The embryo fossils are a millimetre across and seem to be divided into two, four, eight or more compartments. The fossils are a constant size regardless of the number of compartments they are split into - this fits in with a pattern of early embryonic development.

These fossils are potentially so important because the cleavage states they exhibit are very similar to those of modern nematode, flatworm and arthropod embryos. It is therefore possible that these fossils represent diverged metazoan lifeforms older than the Ediacara. They also represent a potential untapped source of Precambrian metazoan fossils, previously overlooked due to their minute size.

Back to: timing of metazoan origins

timing triggers fossils controversies

This report was written by Abby Lane and was last updated on 20th January 1999