LAUSR

Abstract The diversity of Fabaceae in Mexico has a long geological history, and it is particularly rich in sediments from the Oligocene and Miocene. In this work, we describe the first record of two woods resembling ?Cercidoidea and Dialonoidea subfamilies from the Eocene of Chiapas. Both fossil woods have medium to large vessels, abundant paratracheal axial parenchyma, simple perforation plates, short vessel elements, alternate intervessel pits and non-vestured, vessel–ray pits with distinct borders and similar to intervessel pits in size and shape, homocellular (slightly heterocellular) multiseriate rays, prismatic chambered crystals in axial parenchyma cells and in fibers. These characteristics support the inclusion of both woods in Fabaceae. The identification of this new fossil genus (Tzotziloxylon) within Leguminosae, as well as other that have been described earlier from other Eocene localities of Mexico (e.g., Inga, Chamaecrista, and Senna), supports the hypothesis that some genera of this family probably evolved in North America instead of arriving by dispersal from Asia or Africa during the Eocene time.