The cycads, a mostly tropical phylum of gymnosperms, evolved about 300 million years ago and were dominant forms during the age of the dinosaurs. though their sperm are flagellated, their ovules are pollinated by beetles. these beetles get nutrition from the pollen and shelter from the microsporophylls. upon visiting megasporophylls, the beatles transfer pollen to the exposed ovules. in cycads, pollen cones and seed cones are borne on different plants. cycads synthesize neurotoxins, especially in the seeds, that are effective against most animals, including humans. which feature of cycads distinguishes them from most other gymnosperms