WHO LIVES IN A PINEAPPLE UNDER THE EDIACARAN SEA?: NOVEL BIOMINERALIZED FOSSILS FROM THE PATOM UPLIFT, SIBERIA

It has been a longstanding paleontological mystery why unambiguous sponge fossils are not seen in the fossil record until the Cambrian Period despite molecular clock estimates that place their development significantly earlier in the Neoproterozoic. While there are reports of sponge biomarkers and dubiofossils interpreted as sponges from the Precambrian, the rarity, simplicity, and poor preservation of the reported fossils makes them difficult to interpret, as does the common emphasis on the presence of spicules for sponge identification. Following in the tradition of these earlier reports but using a greater variety of morphological evidence, we present novel fossils from the middle Ediacaran of the Patom Uplift in Siberia (approximate age 565 Ma) interpreted as early calcified sponges. The centimeter-scale fossil fragments make up a shell hash and are preserved three dimensionally in a limestone matrix. Petrographic analysis has revealed the presence of smoothly rounded, structurally robust carbonate forms indicating original biomineralization, and the presumably originally organic material interior to the carbonate shell is outlined in pyrite. SEM and EPMA analyses confirm the compositions assessed petrographically, and µCT imaging helps to resolve their three-dimensional structure. While clear spicules have not been found, the fossils show abundant pores and channels which are consistent with a sponge or sponge-grade assignment. The fossils occur coincidently with the Shuram Excursion, a severe negative carbon isotope anomaly, supporting a strong association between Neoproterozoic environmental shifts and the development of animal life. Our discovery supports the presence of sponge-like animals in the fossil record prior to the Cambrian, furthers our understanding of the complexities of Ediacaran ecosystems, and provides a new environmental context in which to understand the appearance of multicellular life on Earth.