Leaves of Menispermaceae and Dioscoreaceae from the Olmos Formation (Upper Cretaceous) from the state of Coahuila, Northern Mexico

Two new species, Menispermites olmosensis sp. nov. (Menispermaceae) and Dioscorites palauensis sp. nov. (Dioscoreaceae) are described from fossil leaves collected in Coahuila state in the late 1970s by Dr. Reinhard Weber. Actinodromous palmate primary venation with craspedodromous secondary veins and the presence of a fimbrial vein, among other attributes, relate it to the extinct genus Menispermites Lesquereux and place Menispermites olmosensis sp. nov. as related to the extant genera Abuta and Odontocarya of the Menispermaceae. These same features relate it to the extinct genus Menispermites Lesquereux. On the other hand, campylodromous primary venation, along with the disposition and course of tertiary veins, show the similarity of Dioscorites palauensis sp. nov. to the Dioscoreaceae. Similar fossil records for the Late Cretaceous suggest that the vegetation distributed in North America was continuous with similar elements to those of the existing tropical rain forests. This approach supports the Boreotropical Hypothesis in the explanation of the origin of modern humid tropical rain forests.