THE BIGGEST SEED FROM THE MESOZOIC AND ITS EVOLUTIONARY IMPLICATIONS

Seed plants are the dominant and most important group in the Earth’s terrestrial ecosystem. In extant angiosperms, seeds vary greatly in dimensions, ranging from 50 μm long to 50 cm long (Bellot 2020,Bellot, et al. 2020 ). In contrast, seed dimension variation is limited in gymnosperms: although Palaeozoic seeds might be much bigger, their Mesozoic peers are much less variable and smaller. Here we report a permineralized gigantic seed with an embryo preserved, Dinospermum gen. nov, from the Lower–Middle Jurassic of Xinjiang, China. As it is the currently largest seed in the Mesozoic, the large size of Dinospermum alone distinguishes it from all known Mesozoic fossil gymnosperms. This makes the affinity and ecology of Dinospermum mysterious. The huge size of Dinospermum suggests that its mother plant had adopted a survival strategy distinct from all known Mesozoic gymnosperms, probably representing a dead end of evolution in the history of plants. The extinction of Dinospermum is a failed K–selection experiment in the evolutionary history of seeds.