Supplementary data from: Early vertebrate biomineralisation and eye structure determined by synchrotron X-ray analyses of Silurian jawless fish

Understanding the origin and early diversification of vertebrates has
always been a challenge because of the ambiguous and conflicting
interpretations of the soft-bodied, pre-biomineralisation fossil record.
Here, we apply synchrotron radiation techniques to Jamoytius and Lasanius,
two soft-bodied Silurian vertebrates, key taxa for discerning vertebrate
bone evolution due to highly localised, but debated, biomineralisation. We
map soft-tissue structures and quantify details of biochemical residue
impossible to resolve with traditional methods. We present the first
unequivocal evidence for biomineralised apatitic scales in Jamoytius by
combining Synchrotron Rapid Scanning X-ray Fluorescence (SRS-XRF) and
Fourier Transform Infra-Red (FTIR) spectroscopy (elevated Ca 37% and P
21%). This approach also recovers robust evidence for apatitic
biomineralisation in Lasanius. Chemical mapping of the optical anatomy of
Jamoytius recovers a close correlation with Zn and Cu distribution,
providing evidence for a retinal pigmented epithelium and complex eyes. In
both taxa, chemical maps reveal original anatomical details not apparent
in visible light, including potential evidence of other sensory anatomy in
Jamoytius. Our work resolves long-standing fundamental anatomical debates,
indicating stem-group origins for bone and complex eyes in vertebrates. We
highlight the potential of using a powerful combination of analytical
techniques to unlock otherwise inaccessible data in problematic fossils.