AFRICAN LEGUME AFFINITIES WITH THE FLORA FROM THE LOWER LA PLATA BASIN (UPPER CENOZOIC), SOUTH AMERICA

Abstract

This article presents an analysis of the affinities of legumes from the upper Cenozoic of the lower La Plata Basin (South America) with extant African genera and their implications for paleoecology and paleophytogeography. Permineralized woods, assigned to Entrerrioxylon victoriensis from the Paraná Formation (Upper Miocene), Gossweilerodendroxylon palmariensis and Paraoxystigma concordiensis from the El Palmar Formation (Upper Pleistocene), and Cylicodiscuxylon paragabunensis from the Arroyo Feliciano Formation (Upper Pleistocene), show affinities with extant genera of the Detarioideae and Caesalpinioideae (mimosoid clade). Today, the taxa of the Detarioideae are distributed mainly in tropical regions of Africa, Central America and South America, and the monotypic genus Cylicodiscus is restricted to West Africa from Sierra Leone to Gabon. Currently, Cylicodiscus, Gossweilerodendron, and Oxystigma are not distributed in South America, which implies that in the past they were widely distributed and became extinct in this region at some point during the Pleistocene–Holocene, presumably related to the climatic changes that occurred during this time. The fossil record of the lower La Plata Basin with taxa related to the Detarioideae and Cylicodiscus supports a wider distribution during the Cenozoic as well as an ancient relationship with the tropical forests of West Africa.