Abstract
The architecture of primary and secondary pinnae of the fossil fern Weichselia reticulata (C. Stokes et Webb) Fontaine is studied based on 28 large specimens from the upper Barremian La Huérguina Formation of the fossil locality Las Hoyas, Cuenca, Spain. The study of the specimens is performed through a morphometric analysis consisting in a reformulation of the Branching Algorithms method of shape description including measurements (insertion angle, distance between pinnae, first segment length and rachis width) and ratios (interval ratio, branching ratio and tapering ratio). A protocol to relocate isolated fragments of fossil pinnae is also established using the interval ratio (distance between pinnae/ previous distance between pinnae) and insertion angle of the pinnae. All specimens show a similar architecture, having elliptic primary pinnae with a sinuous apically tapering primary rachis and triangular secondary pinnae with pinnules of different morphologies. The analysis of the architecture allows to propose that the position of the frond was plagiotropic and that the frond growth was basiplastic for the petiole head and acroplastic for the primary pinnae. The metric method is applied to explore the architecture of four living fern species (Angiopteris evecta (Forst.) Hoffm., Matonia pectinata R.Br., Sphaeropteris cooperi (F.Muell.) R.M.Tryon, and Woodwardia unigemmata (Makino) Nakai). Weichselia architecture results extremely ordered and regular in comparison with the primary pinnae variation of the living species.
Highlights
The most plausible location of the isolated Weichselia fragments along the whole pinna length is ascertained by the comparison of specific variables with those of the most complete specimens
The pattern provided by both variables allows for the repositioning of the small isolated fragments
This study revisits the architecture of the sterile fronds of the fern W. reticulata by measuring the different parts of the frond as a novel approach, which has permitted a detailed description that will be very useful for more accurate reconstructions of this plant in the future
Summary
Stokes et Webb) Fontaine was first described in the Wealden facies of England [1]. Wide distribution and remarkable architecture, Weichselia has received much attention in taxonomy [2,3,4,5], histology [6,7,8], palaeoecology. Metric analysis of fossil and modern fern fronds. 2015 from the Universidad Autonoma de Madrid (http://uam.es/UAM/Home.htm?language=es) for her PhD. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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