On Neuropteris brongniart and Cardiopteridium nathorst from the early carboniferous price formation, southwestern Virginia, U.S.A.

Abstract

Collections of compressions and impressions of fossil plants from several outcrops of the Lower Mississippian Price Formation in southwestern Virginia have yielded numerous well preserved vegetative and reproductive structures, some of which are new and others referable to previously described taxa. Among these are two foliage types, here identified as Cardiopteridium Nathorst and Neuropteris Brongniart, which are more extensively and better preserved than any previously collected ones. They thus represent the first clearly documented occurence of these foliage types in the Lower Carboniferous of North America. Bipinnate fronds terminated by pinnules conforming in every respect to Neuropteris Brongniart are described and are referred to N. antiqua (ex Cycadopteris antiqua Stur). Comparison with the genus Neurocardiopteris Lutz is made and the suggestions of Hartung (1938) and Gothan (1949) that specimen attributed to this genus should be called Neuropteris are supported. A survey of the literature shows that possibly four species of Neuropteris, N. antiqua, N. antecedens, N. broilii and N. loshii, existed in the Early Carboniferous. The specimens referable to Cardiopteridium Nathorst consist of slender axes or portions of bipinnate fronds on which are borne orbicular or reniform pinnules attached by slender pedicles. Pinnule venation is dichotomous, with individual veins converging at the base. The specimens compare best with Cardiopteridium nanum f. spetsbergense described by Walton (1941), Gothan (1949) and Daber (1959) from Early Carboniferous localities in Europe. They are distinguished from isolated pinnules or parts of branch systems of Fryopsis (ex Cardiopteris) by aspects of frond and pinnule morphology. While the affinities of these foliage taxa remain uncertain, present knowledge suggests that Cardiopteridium, on the basis of leaf characters, more likely is the foliage of a progymnosperm or pteridosperm. Neuropteris traditionally has been regarded as foliage of some medullosan pteridosperms although confirmation of attachment is needed; if so, its undoubted presence in the Early Carboniferous constitutes the earliest record of the group.