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Chia-Wei Li,* Jun-Yuan Chen,* Tzu-En Hua
Sponge remains have been identified in the Early Vendian Doushantuo phosphate deposit in central Guizhou (South China), which has an age of ~580 million years ago. Their skeletons consist of siliceous, monaxonal spicules. All are referred to as the Porifera, class Demospongiae. Preserved soft tissues include the epidermis, porocytes, amoebocytes, sclerocytes, and spongocoel. Among thousands of metazoan embryos is a parenchymella-type of sponge larvae having a shoe-shaped morphology and dense peripheral flagella. The presence of possible amphiblastula larva suggests that the calcareous sponges may have an extended history in the Late Precambrian. The fauna indicates that animals lived 40 to 50 million years before the Cambrian Explosion.
Animals appear in the fossil record about 565 million years ago (Ma) in Vendian rocks of the uppermost Proterozoic (1), a time known as the Ediacaran. Most of the Ediacaran fossils are architecturally simple casts and molds, and none of them can be associated without question to extant phyla (2). It is uncertain whether the Ediacaran fauna was the spark of biological diversity that ignited the following Cambrian explosion (I ) or was an evolutional experiment that ended in extinction (3). However, both comparative work on hemoglobin (4) and calibrated rates of nucleotide sequence divergence (5) suggested that there was an extended period of metazoan diversification that began earlier in the mid-Proterozoic, perhaps about 1 billion years ago. The chance of finding the missing metazoan record in the half-billion year long Proterozoic gap was considered to be almost impossible by some, because it was thought that any early animals would be "squishy little larva-like things" that would never have been tough enough to show up in the fossil record (6). The recent finding of phosphatized metazoan embryos from basal Cambrian rocks in China and Siberia (7) indicated, however, that metazoan embryos are probably not uncommon as fossils but have been overlooked because of their minute size and nondescript morphology. Here, we describe an assemblage of well-preserved sponge fossils from the Doushantuo phosphate deposit (central Guizhou, China) of Early Vendian age, ~580 Ma (8).
Sponges are the most primitive metazoans and their presence in the late Proterozoic has been expected by molecular and morphological phylogenies (9). Occurrences of the late Proterozoic...