Fossil woods (Malvaceae) from the lower Miocene (early to mid-Burdigalian) part of the Cucaracha Formation of Panama (Central America) and their biogeographic implications

Abstract

Nine fossil wood specimens are described from the Miocene (early to mid-Burdigalian) part of the Cucaracha Formation of Panama, Central America. The calcareous permineralised fossils, which contain Teredolites borings, occur in erosive-based pebbly conglomerate lenses, interpreted as tidally influenced fluvial channels. All specimens show tile cells characteristic of many clades of the diverse and widespread family Malvaceae sensu APG III. Fossils were identified, more precisely, through searches of the Insidewood Database, and detailed study of comparative extant material. Two novel types of fossil wood occur: (1) Guazumaoxylon miocenica gen. et sp. nov shows paratracheal axial parenchyma with a broad-sheath to winged-aliform distribution combined with intermediate-type tile cells, similar to tropical South American species of Guazuma (subfamily Byttnerioideae) and (2) Periplanetoxylon panamense gen. et sp. nov shows apotracheal axial parenchyma in irregular to regular bands >3 cells wide combined with Pterospermum-type tile cells, similar to tropical South American species of Pentaplaris (subfamily Malvoideae). The occurrence of fossils showing similarities to extant South American taxa in the Miocene of Panama is of palaeogeographic significance, suggesting intercontinental exchange of tree species at least ten million years before the traditional date for the final closure of the Panama Isthmus.