Where's the glass? Biomarkers, molecular clocks, and microRNAs suggest a 200‐Myr missing Precambrian fossil record of siliceous sponge spicules

@article{Sperling2010WheresTG,
  title={Where's the glass? Biomarkers, molecular clocks, and microRNAs suggest a 200‐Myr missing Precambrian fossil record of siliceous sponge spicules},
  author={Erik A. Sperling and J. Mike Robinson and Davide Pisani and Kevin J. Peterson},
  journal={Geobiology},
  year={2010},
  volume={8}
}
The earliest evidence for animal life comes from the fossil record of 24‐isopropylcholestane, a sterane found in Cryogenian deposits, and whose precursors are found in modern demosponges, but not choanoflagellates, calcareans, hexactinellids, or eumetazoans. However, many modern demosponges are also characterized by the presence of siliceous spicules, and there are no convincing demosponge spicules in strata older than the Cambrian. This temporal disparity highlights a problem with our… 

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