“Fossil woods from the Miocene of Costa Rica and Nicaragua: Insights into the Neotropical floral puzzle”

Abstract

The fossil record of Central America plays a pivotal role in our comprehensive understanding of the Neotropical Flora. It represents a mosaic of elements from South America that migrated to North America and vice versa, contributing to the rich diversity of flora we observe today. Despite the importance of Central America's vegetation history, our knowledge remains fragmented, with limited information available for regions like Costa Rica and Nicaragua. This study presents findings based on the first five wood samples collected from Miocene sites in Costa Rica and Nicaragua, situated across slopes ranging from 10 to 1000 m above sea level, reminiscent of tropical environments. These specimens exhibit common characteristics such as a median vessel element diameter of 100–200 μm, small to medium - sized alternate inter - vessel pits, relatively thin and slightly heterogeneous rays spanning 1 to 3 cells in thickness, and a prevalence of procumbent cells. Additionally, we observed vasicentric and thin - banded axial parenchyma, thin - walled fibers, and the presence of few gums and tyloses. The variability in these features suggests the presence of taxa belonging to families such as Sapotaceae (cf. Vitellaria), Leguminosae (cf. Aphanocalyx and cf. Dalbergia), Malvaceae/Sterculiodeiae (cf. Cola), and Myrtaceae (cf. Eucalyptus), most of which have been reported in both North and South America. Therefore, understanding the timing of their arrival and their biogeographic histories is crucial for elucidating the origins and composition of today's Neotropical Flora. Our findings challenge the simplistic narrative of recent migration from southern and northern floras shaping the Neotropical Flora. Instead, they underscore the complexity of its evolutionary history, highlighting the intricate interplay of various taxa over time to generate this unique tropical assemblage.