TWO COEXISTING, PERMINERALIZED ALETHOPTERISMORPHOLOGIES FROM IOWA AND A NEW METHOD FORDIFFERENTIATING THEM BASED ON LEAF GEOMETRY

摘要

This research focuses on a new morphology of Alethopteris, the frond of aCarboniferous seed-fern tree, based on a series of orthogonal cross-sections of theleaflets, which are preserved in coal balls. The coal balls, which are chunks of coalsaturated in calcium carbonate, were recovered from the Williamson No. 3 Mine inLucas County, Iowa. From close examination of already prepared and sectioned coalballs, I identified criteria that distinguish the new Alethopteris morphology from otherAlethopteris morphologies in the same coal bed and even coal balls. These criteriaconsisted primarily of measures made on orthogonal cross-sections. Results ofcomparisons of two populations of Alethopteris from the Williamson No. 3 Mine usingthe student t-test suggest that the two morphologies differ significantly and hence, aredifferent species. I compared the new Williamson No. 3 Alethopteris morphology toAlethopteris species known from other coal ball localities. The new Williamson No. 3Alethopteris is different from all these species, and represents a new species.