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..., , # CT scanning of the left partial femur of *Keichousaurus* for microtubes reconstruction

Dataset DOI: [10.5061/dryad.h70rxwdwg](10.5061/dryad.h70rxwdwg)

## Description of the data and file structure

A small piece of the left femur of CUG VH232 was scanned using ZEISS Xradia 620 Versa at Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences. The bone was broken at the middle region, and the resulting sample was scanned over the thickness of the compact bone only, from the periphery to the inner cortex, in order to maximize resolution. For the scan, the acceleration voltage was set to 100 KV and current to 140 μA, and the voxel size to 0.8106 μm^3. The exposure time for each projection was 2 s, and the number of TIFF images obtained was 3201.

### Files and variables

#### File: Raw\_Tiffs-VH232\_LFP\_4X-LE4-90kv-12w-2s-0.8104-3201-DR.zip

**Description:** CT Scanning images (TIFF format) of the left partial femur of *Keichousaurus* from the Middle Triassic of Sou...,