Impressions of "seed ferns" Alethopteris, (center, with smaller leaves), and Neuropteris, (surrounging Alephopteris), with individual leaves of Cyclopteris, (base leaves of Neuropteris), at lower right. All common to the Pennsylvanian Epoch, Carboniferous Period, some 300 million years ago. Though their foliage resembled that of true ferns, prehistoric "seed ferns" were among the first seed-bearing plants (gymnosperms) and the precursors of most plants living today. Specimen courtesy Pennsylvania State Museum, Klose Coal Fossil Collection.