The spiniest seeds found in Mid-Cretaceous Myanmar amber.

Although angiosperms occurred earlier, their radiation did not occur until the Middle Cretaceous. Owing to a lack of knowledge of early angiosperms, this radiation used to be mistaken for the origin of angiosperms and became Darwin's "abominable mystery". Palaeobotanical progresses in recent decades have released more information on early angiosperms, especially their Middle Cretaceous radiation. The fossil angiosperms from Myanmar amber shed unique light on the evolution and diversity of angiosperms due to their exquisite preservation. To enhance our understanding of this fossil lägerstatte, here we report a new fossil angiosperm named Spinograna myanmarensis gen. et sp. nov. from Myanmar amber. The fossil is a fruit bearing spiny seeds. Its seeds are unique in morphology: they are discoid in form, with marginal furcated spines. This unique morphology represents an extremity in seeds: it is the spiniest seed in plant history, implying that they were dispersed by animals, a fact that remains unknown hitherto. The discovery of Spinograna indicates that the ecosystem in the Middle Cretaceous is much more complicated than previously thought, and some of the ecological ties between plants and animals that existed then have gone out forever.