Data from: The earliest known fungal-induced biomineralization in fossil bones, and its role in the marine ecosystem

Formation of microtubes, defined as small internal borings, in fossil and
modern bone is a well-attested phenomenon. However, determining whether
microtubes were created by microbial activity or abiotic processes is
challenging, particularly in fossils. Here, we report abundant microtubes
in compact bone from numerous specimens of the marine reptile
Keichousaurus from the Middle Triassic of southwestern China. Light and
scanning electron microscope imaging of osteological thin sections, and
CT-based 3D reconstruction of the microtubes, reveal geometric features
typical of fungal hyphae, such as bifurcation and tight helical coiling.
Some microtubes contain what may be the first known fossilized fungal
vacuoles. The microtubes are thus likely to be of fungal origin, produced
by saprobic marine fungi during decomposition. Furthermore, fluorine is
abundant in the compact bone, and even more prevalent in the infillings
that occur in many microtubes. The fungi evidently released calcium ions
and took up fluorine from the reptiles’ bodies, and promoted the formation
of fluorite in the microtubes. The infillings represent the earliest known
instance of fungal-induced biomineralization within fossil bone,
demonstrating that some Middle Triassic fungi were capable of impacting
global biogeochemical cycling by taking up substantial amounts of
fluorine.