266 The Neoproterozoic Earth and Life Co-evolution (Posters)

This session aims to enhance discussions and foster interdisciplinary collaborations to advance understanding of the Neoproterozoic Earth and life co-evolution. Contributions from paleontologists, geochemists, sedimentologists, Earth system modelers, and related fields are highly encouraged.

Wednesday, 22 October 2025
8:00 AM - 5:30 PM
HBGCC, Hall 1

New Microstructural Analysis of the Apatitic Scale Microfossils

Paper number: 266-9
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

  • Emily Felder Presenting Author
    University of California, Santa Barbara, Santa Barbara, CA
  • Susannah Porter
    University of California, Santa Barbara, Santa Barbara, California
  • Leigh Anne Riedman
    University of California, Santa Barbara, Santa Barbara, California

Abstract

Many eukaryotic organisms form shells, scales, bones, and other crystalline structures according to a specific crystal habit and organic template. This process of biomineralization has evolved repeatedly across the eukaryotic tree with varied biomineral compositions, cellular mechanisms of mineral formation, and microstructures whose architectural units can often resolve phylogenetic relationships. Some of the earliest shells formed by animals have complex microstructures; microstructural diversity among molluscs was already established by the mid-Cambrian, distinguished by unique shell fabrications including cross-bladed, fibrous, and prismatic crystal morphologies (Vendrasco et al., 2016). Protists can also form skeletons with complex microstructures, with even the earliest biomineralizing protistan fossils, the 717–812 Ma apatitic scale microfossils (ASMs), showing evidence of microstructural diversity and complexity. First discovered in thin sections of chert-hosted limestone from the Fifteenmile Group, Yukon Territory by Allison and Hilgert in the 1980s, ASMs exhibit a wide range of complex scale morphologies, including hexagonal pores, protruding barbs, rimmed spines, and other woven and fibrous scaffolding. Though initially thought to be composed of silica, further study in the 2010s showed they were composed of interwoven bundles of hydroxyapatite and kerogen to form lattice frameworks (Cohen et al., 2011; Cohen et al., 2017). We have access to the original Fifteenmile Group samples collected in 1979 by Awramik and Allison and have now extracted both previously identified species and what appear to be 9 new species, adding to the 38 already described, based in part on what appear to be differences in microstructural fabrics. For example, some scales have raised outer rims that have an undetermined structural orientation and construction when compared to the interwoven, bundled fibers of the inner scales. This research aims to document the variety of microstructures exhibited by ASM scales, including the relationship between the kerogen and crystallites.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-412242

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