Fig. 4 The histology of Whatcheeria femora from size class IV. Under polarized light and a lambda filter, FMNH PR 5023 contains an abundant trabecular network in the medullary cavity and a narrow cortex (a). The cortex is composed primarily of lamellar bone (b, c) with some secondary remodeling (c). The trabeculae in this specimen are well-developed and composed of lamellar tissue (d). These general observations are consistent with an additional specimen, FMNH PR 1958, visualized with µCT imaging (e), including a developed trabecular network in the medullary cavity and a narrow lamellar cortex (f). In a and e the adductor crest (ventral) is oriented towards the bottom and marked with an asterisk. Abbreviations: lfb lamellar-fibered bone, mc medullary cavity, pfb parallel-fibered bone, so secondary osteon, tr trabeculae. Scale bars: a, e = 5 mm; b, f = 250 µm; c, d = 100 µm.

Published as part of Whitney, Megan R., Otoo, Benjamin K. A., Angielczyk, Kenneth D. & Pierce, Stephanie E., 2022, Fossil bone histology reveals ancient origins for rapid juvenile growth in tetrapods, pp. 1-9 in Communications Biology 5 (1) on page 6, DOI: 10.1038/s42003-022-04079-0, http://zenodo.org/record/7390744