Extended Data Figure 3 : Midshaft bone histology of two Acanthostega humeri (UMZC T.1295 and MGUH 29019).

From: Life history of the stem tetrapod Acanthostega revealed by synchrotron microtomography

Extended Data Figure 3

a, Three-dimensional model of humerus UMZC T.1295 in dorsal view and oriented with the proximal epiphyses6 towards the top. The white circle indicates the midshaft location at which the transverse virtual section was made. The latter (single tomographic slice, voxel size: 0.638 μm) shows the complete bone deposit of cortical bone (c) from the mineralization front (mf) to the surface of the humerus (top). The cortical bone comprises numerous osteocyte lacunae (ol), which are much smaller than the aligned globular cell lacunae (agl) present at the location of the mineralization front. Trabeculae (t) are numerous in the medullary cavity. The red line in the transverse virtual section indicates the location of the next tangential virtual section which details the mineralization front. b, Three-dimensional model of the humerus MGUH 29019 in ventral view showing the high-resolution scanned location. The virtual section shows the humeral cortical histology at the midshaft (single tomographic slice, voxel size: 0.638 μm). As in UMZC T.1295, the cortical bone matrix (cb) is very compact, pierced with small osteocyte lacunae. At this location, its surface (top), although still embedded in the rock matrix, is not well preserved. The red line in the transverse virtual section indicates the location of the next tangential virtual section detailing the cellular structure of the mineralization front.