Williamsonia carolinensis sp. nov. and associated Eoginkgoites foliage from the Upper Triassic Pekin Formation: Implications for early evolution in Williamsoniaceae (Bennettitales)

摘要

Premise of research. Few reproductive organs unequivocally attributable to the important but enigmatic Mesozoic seed plant order Bennettitales have been described from the Triassic of all of North America outside of Greenland. Here, the first ovulate reproductive organs (gynoecia) of the group from the Upper Triassic of eastern North America are described and assigned to a proposed new species, Williamsonia carolinensis, of the family Williamsoniaceae. Methodology. The excellently preserved plant fossils were investigated using cuticular analysis and light, fluorescence, and scanning electron microscopy. Pivotal results. The description is based on 10 specimens from the Late Triassic (Carnian) Pekin Formation of North Carolina. They are interpreted as representing progressive developmental stages. Williamsonia carolinensis lacks a corona (sterile apical projection of the receptacle) and bracts subtending the receptacle. The lack of bracts is particularly unusual and appears to be the original condition and not apreservation artifact based on their absence even on immature specimens. The two largest specimens, interpreted as mature gynoecia, occur together on the same slab in exclusive association with the unusual bennettitalean leaf Eoginkgoites, suggesting that these organs were produced by the same parent plant species. Conclusions. The unique features of W. carolinensis, along with the probable affinity with Eoginkgoites foliage, expands the known diversity of the Williamsoniaceae and supports previous suggestions of remarkably high levels of morphological disparity in the earliest history of the Bennettitales.