A morphometrics-informed reconstruction of the Early Devonian zosterophyll Nowenia matsunagae gen. et sp. nov. as a template for building detailed empirically supported whole-plant concepts of early tracheophytes with simple body plans

BACKGROUND AND AIMS: The fragmentary state of plant fossils and the modular organization of plants make whole-plant reconstructions of fossil species desirable and feasible. Such reconstructions are key for integrating fossil species in systematic studies. The ∼410 Ma Beartooth Butte Formation of Wyoming (USA) hosts the only rich Early Devonian flora in western North America, which fills a major gap in the phytogeography of this interval. We construct a whole-plant concept for a new zosterophyll from the Beartooth Butte Formation based on detailed morphometric study of a large number of specimens. METHODS: More than 600 fragments of the new zosterophyll were observed and 200 of these were measured. Epidermal features were observed in cuticular material recovered on cellulose acetate. Resulting data were used to characterize variability in axis thickness and taper, branching density and sporangial orientation, based on descriptive statistics, correlations and principal component analysis. KEY RESULTS: The new zosterophyll, Nowenia matsunagae gen. et sp. nov., consisted of decumbent axes with long internodes that exhibited K-branching and bore more densely branched erect axes, as well as branches with delayed development (dormant lateral meristems and circinate protrusions). Axes had circinate apices and bore isolated bivalvate sporangia in small numbers, primarily on upright portions. Phylogenetic analyses recover Nowenia sister to Forania, from which it differs primarily in the absence of spinescent protrusions. CONCLUSIONS: Nowenia is the first zosterophyll for which an empirically based whole-plant concept that makes explicit and extensive use of quantitative data is available. The approach used to reconstruct the Nowenia plant introduces a method for integrating morphometric data in constructing whole-plant concepts of early tracheophytes with simple body plans. Application of this and similar methods to additional fossil species could produce reconstructions at similar levels of detail and accuracy, crucial for reaching well-supported resolution of early vascular plant relationships.