Figure 4

Transverse thin section images of the right femur from NMV P186047, and hand sample images of the right femur and left tibia of NMV P186047. (a) Composite image of complete femur thin section. Although the specimen is badly crushed, microstructures are still visible for descriptive purposes. Blue letters reference the magnified regions shown in corresponding panels. Plane polarized light. (b) A small region of incipient fibro-lamellar bone is present on the anterior and medial sides of the innermost cortex. Otherwise, bone fibre orientation throughout the cortex is parallel-fibred with longitudinal or anastomosing simple vascular canals. Circularly polarized light. (c) Four LAGs are visible within the inner to mid-cortex (arrows). The two LAGs within the annulus (blue arrows) do not merge, and so are considered to represent the growth hiatus of two years. Plane polarized light. (d) Bone fibre orientation is more avascular and increasingly lamellar near the periosteal surface, forming an EFS. There is one LAG at the onset of the EFS and another present within the EFS (arrows). Plane polarized light. EFS = external fundamental system. (e) Photographs of the right, non-pathologic femur and the left pathologic tibia of NMV P186047. Blue lines show locations of transverse thin section slides produced from the fossils.