Assessing the veracity of Precambrian ‘sponge’ fossils using in situ nanoscale analytical techniques

Abstract

Paleontological inferences, molecular clocks, and biomarker fossils indicate sponges evolved in the Cryogenian, but Precambrian sponge fossils are rare, poorly substantiated, and controversial. Spicule-like microstructures (SLMs) hosted in phosphatized fossils from the Ediacaran Doushantuo Formation (~635-551 Ma) at Weng'an of South China have been interpreted as cylindrical siliceous monaxons, and their hosting fossils as the oldest demosponges in the fossil record. In order to assess their veracity as the oldest spiculate demosponges, we utilize a suite of in situ nanoscale analytical techniques-including scanning electron microscopy, synchrotron Xray fluorescence mapping, X-ray absorption near edge structure (XANES) spectroscopy, focused ion beam electron microscopy, and transmission electron microscopy-to evaluate the ultrastructures and elemental, chemical, and mineralogical compositions of the SLMs. Our data decisively shows that the SLMs are carbonaceous in composition and rectangular in transverse sections, and therefore, are not cylindrical siliceous spicules. Instead, the SLMs may be microbial strands, axial filaments of early hexactinellids, or acicular crystals molded by organic

Anoxia can increase the rate of decay for cnidarian tissue: UsingActinia equinato understand the early fossil record

“…The Cambrian Explosion—a dramatic increase in the abundance of animal fossils during the Cambrian Period (Marshall, )—is variably interpreted to reflect a real biological diversification (Antcliffe et al, ; Budd & Jensen, ; Daley, Antcliffe, Drage, & Pates, ) or merely an explosion of fossils with a very deep root for the origin of animals in the Precambrian (Erwin et al, ). The problem of identifying the earliest cnidarian fossils in many ways encapsulates the difficulties of resolving the first appearance of the Metazoa and are just as crucial as the debate taking place about the earliest sponge fossils (Antcliffe, , ; Antcliffe et al, ; Gold, Grabenstatter, et al, ; Gold, O'Reilly, Luo, Briggs, & Summons, ; Love et al, ; Muscente, Michel, Dale, & Xiao, ; Nettersheim et al, ). Despite this importance few experimental insights are available for any taxa other than the Bilateria.…”

Sedimentological perspectives on climatic, atmospheric and environmental change in the Neoproterozoic Era

“…() which post‐dates the critique, were dismissed by Antcliffe et al . () and the view was expressed that there is currently no convincing fossil evidence for crown‐group sponges prior to reliable fossil sponge spicules from the lower Cambrian succession in Iran at 535 Ma (Antcliffe et al ., ; Muscente et al ., ). Earlier prominent claims of spicules in South China from 580 Ma (Li et al ., ) proved to have a diagenetic origin (Yin et al ., ).…”

Resolving Three-Dimensional and Subsurficial Features of Carbonaceous Compressions and Shelly Fossils Using Backscattered Electron Scanning Electron Microscopy (Bse-Sem)

“…The ECL is covered by nanometer-to micrometer-sized holes (Fig. 7I), suggesting it is made of porous material, similar to nanoporous organic matter making up carbonaceous fossils (Schiffbauer et al 2007;Schiffbauer and Xiao 2009;Pang et al 2013;Muscente et al 2015). In some places, the ECL contains granular microstructures, which produce greater signal than surrounding carbonaceous material (Figs.…”