Figure 3: Microscale analysis of the Ophthalmosaurus bones.

(a) Bone covered by a peloidal crust (arrows). The bones are enclosed in a siliciclastic matrix cemented by microsparite. In the right side of the photo, articulated bivalve filled with secondary sparry calcite and microsparite. (b) Detail of the peloidal crust, made by clotted micrite and loosely spaced micritic peloids (arrows). (c) Detail of the peloidal crust. Clotted micrite and pyrite in the upper part; elongated mats representing calcified biofilms in the lower part. (d) Fossil bone extensively bioeroded (white arrows point to microborings), showing a thick micrite rim on the outer side. Bone lacunae are filled with pyrite (black arrow). (e) Close-up of the bioeroded area where microborings are perpendicular to the external bone surface. (f) Empty, elongated microboring. (g) Microboring filled with a pyrite framboid. (h) Cancellous bones filled with clotted micrite, microsparite and sparry calcite. (i) Clotted micrite, pyrite and microbial peloids (arrows) filling the voids of cancellous bones. (j) Pyrite filling cancellous bones decreases in abundance towards the bone centre, and is rare in the surrounding concretion. All transmitted light photomicrographs in plane-polarized light except (j) in reflected light; (f) SEM (scanning electron microscope) image in secondary electron mode, (g) SEM in backscattered electron mode. ib, ichthyosaur bone; sc, sparry calcite; ms, microsparite; ec, enclosing concretion; cm, clotted micrite; py, pyrite. Scale bars, (a) 500 μm; (b,h,j) 200 μm; (c,d,i) 100 μm; (e) 20 μm; (f) 10 μm; (g) 2 μm.