Basal sauropodomorph eggshell microstructure and their respective Sinemurian localities (crosses) among the Rhaetian (green) to Sinemurian (red) global record of sauropodomorph fossil sites (circles). (a–f), Lufengosaurus (Chuxiong Prefectural Museum, catalogue no. C2019 2A233), (g,h), Mussaurus (Instituto ‘Miguel Lillo”, Tucuman, catalogue no. PVL 5965), (i–k), Massospondylus (Bernard Price Institute of Palaeontology, University of Witwatersrand, catalogue no. BP/1/5254). (a) Section through nugget containing numerous Lufengosaurus eggshell fragments (plane polarized light, ppl). (b), close-up (ppl) of a Lufengosaurus eggshell fragment, showing calcite crystals of the mammillary layer radiating from an organic core embedded in the eggshell membrane. (c) As in (b) under cross polarized light (xpl), highlighting the calcite crystals of a mammillary cone. (d) Different xpl view with lambda waveplate, e. line drawing of (d). (f) Lufengosaurus cathodoluminescence view with 880 nm filter. (g) Mussaurus eggshell, showing thick eggshell membrane, and distorted calcareous layer. (h) Line drawing of (g). (i) Massospondylus eggshell fragment (ppl), showing wedges in the calcareous layer, and a homogenous eggshell membrane. (j), Line drawing of (i). (k) Massospondylus cathodoluminescence view with 880 nm filter. Scale bars: in (a): 1 mm, (b–f,k): 50 µm, (g–j): 100 µm. Abbreviations: cl, calcareous layer; cw, crystal wedges of calcareous layer; em, eggshell membrane; ps, pore space; su, shell unit. See also Figs S1–S3. (Map from66 with permission).