A fruit and leaves of Rhamnaceous affinities from the late Cretaceous (Maastrichtian) of Colombia

Abstract

Although Rhamnaceae are distributed worldwide today, the former hypothesis for its Laurasian origins may need to be reconsidered in view of recently discovered fossils from the Guaduas Formation of central Colombia ([~]68 Ma), including fossil leaves (Berhamniphyllum) and a fruit (Archaeopaliurus boyacensis). Recent phylogenetic studies calibrate the stem of Rhamnaceae at 64 Ma and divide the family into three groups, rhamnoid, ampeloziziphoid, and ziziphoid. Although the fruit, Archaeopaliurus boyacensis, resembles that of Paliurus and suggests a relationship to the Paliureae in the ziziphoid group, associated leaves of Berhamniphyllum conform in architecture to those found today only in the Rhamneae tribe. The Maastrichtian age of these fossils predates the ages previously estimated for the Rhamneae tribe (28.5 Ma) and the Paliureae tribe (31.6 Ma) using a modified clock approach. Based on the new megafossil evidence, two alternative ideas are proposed: (1) that these fossils predate the extant tribes or (2) that the family diversified into modern tribes earlier than previously proposed.