Abstract Detail


Gensel, Patricia [1], Knier, Aubrey [2].

Novel leaf morphology and variation in foliage similar to Rhacopteris from the Early Carboniferous Price Formation, southwestern Virginia, USA .

Leaves similar to the European foliage genus Rhacopteris, of probable seed plant affinity, were obtained from an outcrop of the Early Carboniferous Price Formation near Pulaski, Virginia.  Numerous impressions, some representing complete leaves, demonstrate a once-pinnately compound leaf, with a central rachis bearing opposite to sub-opposite leaflets that change in size and shape along its length, ranging from rhomboidal to flabelliform.  Margins are crenate and venation is dichotomous.  Leaflets are oriented at an angle from the plane of the rachis.   Some leaflets on a subset of specimens that includes many of the more complete leaves are deeply bilobed, a feature not recorded for previously described Rhacopteris species.   To determine if one or several taxa are present, measurements were made of leaflet length, leaflet perimeter, leaflet surface area, rachis internode length, and depth of lobing using ImageJ. In some specimens, leaflets were elongated to distorted, probably by diagenetic effects at the time of post-depositional mountain uplift in that area.   Simulations of undistorted leaf images to produce the type of distortion resulting from tectonic uplift and slickensiding (present in the material) were made and support that these elongated leaves are taphonomically distorted.  Comparison of the measured parameters between the Virginia specimens and several published Rhacopteris species, mainly on specimens with bilobed leaflets, showed that differences occur in internode distance, range of surface area (although averages were similar), and depth of leaflet lobing.  When considered as disarticulated entities, these leaves exhibit variation recognized as different species in previously described specimens of the “morphotaxon” Rhacopteris.   Given the leaves are restricted to one sediment horizon and form more than 80% of plants preserved there, their variation instead might represent differences in leaves from a single plant, the leaves differing depending on location or ontogenetic position.  Leaves with the distinctive bilobed leaflets differ enough to represent a new taxon, at least at the species level.  Whether referable to one or more taxonomic entities, this foliage increases floral diversity and may represent the first undoubted occurrence of a Rhacopteris type leaf in the Early Carboniferous of North America. 

1 - University Of North Carolina, Department Of Biology, CB# 3280, Coker Hall, Chapel Hill, NC, 27599, United States
2 - University of North Carolina Chapel Hill, Biology Dept., Coker Hall, South Road, Chapel Hill, NC, 27599, United States

Early Carboniferous

Presentation Type: Oral Paper
Session: PAL3, Paleobotany I: Paleozoic and Mesozoic Paleobotany
Location: Virtual/Virtual
Date: Tuesday, July 28th, 2020
Time: 10:00 AM
Number: PAL3001
Abstract ID:736
Candidate for Awards:None

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