Newly uncovered amorphous fossils from black shale formations of the Francevillian Basin in Gabon, Africa hint that multicellular life may have evolved more than 2 billion years ago -- some 200 million years earlier than previously expected, according to a study published last week in Nature. A. El Albani, et al., "Large colonial organisms with coordinated growth in oxygenated environments 2.1 Gyr ago,"Nature, 466:100-4, 2010.
Sedimentologist Abderrazak El Albani of the University of Poitiers in France and his colleagues discovered more than 250 specimens at the site, all dating to approximately 2.1 billion years ago, and ranging up to 12 centimeters in length. Chemical analyses confirmed the biological origin of the fossils, which are now composed of the iron-sulfide mineral pyrite that replaced the organic tissue as the organism decomposed. Interestingly, these fossils appear just a couple million years after the Great Oxidation Event, when oxygen became more widely available in the atmosphere and in the shallow oceans. This may have facilitated the evolution of a thicker organism (cells in the middle have greater difficulty obtaining oxygen if it's only at trace levels in the atmosphere). And their large and complex structures, as revealed through X-ray microtomography, are indicative of cell-to-cell signaling and coordinated growth between cells. Specifically, the fossils display scalloped edges with radiating slits, and many have a central structure, not unlike the overall structure of a jellyfish medusa. Unfortunately, the insides are not preserved, so it is hard to prove multicellularity, but their size, complexity and organization of structure indicate multicellularity. Of course, there is debate on the definition of multicellularity itself, as the molecular machinery for cell-to-cell communication is found in more primitive organisms like bacterial colonies.
Unfortunately, according to one of the authors, there aren't many other fossils of that age to corroborate the connection (most of the rocks of that time have been destroyed, and the ones remaining are not pristine enough to find delicate fossil structures). Why? Is this due to mining? It's a shame. Regardless, it's important to realize that although these may be the oldest known multicellular organisms, multicellularity has evolved at least 20 times even among living lineages and thus, these are not necessarily the ancestors of all multicellular life.