Reinvestigating the fossil leaf Welwitschiophyllum brasiliense Dilcher et al. (2005), from the Lower Cretaceous Crato Formation of Brazil

Abstract

The Lower Cretaceous Crato Formation of north-east Brazil yields a diverse plant assemblage. It has yielded many macrofossils thought to be related to the enigmatic gymnosperm group Gnetales, including the long leaf Welwitschiophyllum brasiliense Dilcher et al. 2005. This fossil plant is considered to be related to the extant gnetalean Welwitschia mirabilis Hooker 1863, despite lacking many gnetalean characteristics. Presently, this macrophyte fossil is known only from detached leaves and much anatomical information is currently unavailable. The reproductive structures assigned to the family Welwitschiaceae in the Crato Formation, as well as several key morphological features of the leaves are currently thought to relate fossil Welwitschiophyllum to extant Welwitschia. These leaf characters include: isobilateral leaf form, triangular elongated leaf shape with a wide base, longitudinal splitting from a frayed leaf apex, numerous parallel veins and possible thickening of the epidermis. However, several of these leaf characteristics also occur in many other macrophytes, perhaps as a result of convergence. Anatomical and morphological data described here from fossil Welwitschiophyllum leaves is compared with extant Welwitschia. Our results show that Welwitschiophyllum can only be placed tentatively in Gnetales, as many of the features we report are not diagnostic, and may have resulted from convergent evolution (e.g., gum). Fossils with better anatomical preservation and the reconstruction of the whole plant are really needed to better understand the affinities of Welwitschiophyllum.