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Otavia antiqua is an ancient sponge-like multicellular organism found in the Otavi Group (the generic name being the namesake) in the Etosha National Park, Namibia. It is claimed to be the oldest animal fossil, being found in rock aged between 760 and 550 million years ago. The oldest Otavia fossils are from the Tonian period, before the Snowball Earth, but the latest found were from the Nama Group rocks of the Ediacaran period.
The affinities of these fossils, along with other paleontological evidence for Precambrian sponges, are disputed.
Some researchers propose that Otavia antiqua may have evolved over 100 million years earlier than previously thought, which supports the ‘molecular clock’ predictions that sponges were among the first animals to appear.
Some scientists theorized that the burial of Otavia may have actually contributed to carbon burial and to the rising in oxygen levels during the Neoproterozoic. Furthermore, Otavia antiqua fossils are present in strata both before and after major glaciation events, indicating the organism may have survived the extreme conditions of ‘Snowball Earth’.
Otavia antiqua fossils have more complex internal anatomical features, including small incurrent pores (ostia), layered chambered labyrinths, and cavities which are connected to larger excurrent openings (oscula), consistent with a sponge-like body plan. The internal cavities are often filled with geopetal sediment, suggesting the organisms were hollow during life and infilled after death. Their structure also lacks features typical of microbial fossils, supporting an animal rather than microbial origin.
The material of the outer wall is predominantly calcium phosphate. In addition to calcium phosphate, the fossils also contain calcite and dolomite.
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