Oldest animal fossil: bacteria
The world’s oldest fossilized embryos that made the cover of Nature in 1998 may actually be gigantic bacteria according to Jake Bailey of USC. The bacterium in question, the worlds largest, is one Thiomargaria, which has a unique feature of promoting deposition of phosphorite. Coincidentally, China’s Doushantuo Formation where the fossils were found is teeming with the rare mineral. What prompted the original misidentification was likely the traces of reductive cell division, typical of animal embryos, but also found in some baceteria e.g. Thiomargarita. Putting two and two together, Bailey arrived at his conclusion that the 600-million year old phosphorite-rich Precambrian fossil was likely a Thiomargarita ancestor. His study is published in selfsame Nature that ran the original cover-story almost 9 years ago.
Oldest animal fossils may have been bacteria, EurekAlert.org