Cycadeoidea

Cycadeoidea is an extinct order of seed plants that flourished during the Mesozoic Era, particularly from the Late Triassic to the Late Cretaceous periods, approximately 220 to 66 million years ago. These plants are notable for their cycad-like appearance, which includes a robust trunk, pinnate or palmate leaves, and reproductive structures resembling cones. Cycadeoidea is often considered a basal group within the cycad order (Cycadales), though some classifications treat it as a distinct lineage closely related to modern cycads.

Fossil evidence of Cycadeoidea is primarily found in the form of leaves, stems, and reproductive organs, with entire specimens being rare. The group is characterized by its large, compound leaves that often exhibit parallel venation, similar to those of modern cycads. Some species possessed woody trunks, while others were herbaceous or shrub-like. The reproductive structures of Cycadeoidea typically include separate male and female cones, with pollen cones producing wind-dispersed spores and seed cones bearing ovules that develop into seeds.

Cycadeoidea plants likely played significant ecological roles in their environments, serving as food sources for herbivorous dinosaurs and other early reptiles. Their fossil record provides valuable insights into the evolution of seed plants and the diversification of gymnosperms during the Mesozoic. While closely related to modern cycads, Cycadeoidea represents an extinct lineage that did not survive past the Cretaceous-Paleogene extinction event, which marked the demise of the non-avian dinosaurs and many other Mesozoic flora and fauna.