Fig 4. Structure and composition of preserved mylospheres from Macrotermitinae chamber.

(A) Image of polished surface from sample RRBP 08248g (Colony 1) exposing compressed mylospheres (white) near the nest wall and detrital sediment (dark red) filling the chamber. Morphologies and chemical compositions were analyzed via energy dispersive spectroscopy (EDS) and backscattered electron imaging (BSE) by electron probe microanalysis. The sediment surrounding the mylospheres is clay-rich and contains occasional detrital quartz and feldspar grains (and accessory minerals such as monazite), deposited as the nest walls were expanded and/or through infilling of the chamber during construction of or later burial of the nest. There is a small presence of diagenetic Fe-, Mn-, and Ti-rich cement. (B) BSE image of a mylosphere from (A) revealing a homogeneous composition. Filled and hollow subcylindrical, 5–10 μm particles with a major Ca component comprise the mylospheres. We interpret the mylospheres to be composed of wood fragments now replaced by calcium carbonate, preserving the remnants of macerated cellulose and tracheids (Fig 2B).