A new Oligocene-Miocene tree from Panama and historical Anacardium migration patterns

Abstract

Migration of Boreotropical megathermal taxa during the Oligocene and Miocene played a key role in assembling diversity in tropical regions. Despite scattered fossil reports, the cashew genus Anacardium offers an excellent example of such migration. The fossil woods described here come from localities in Veraguas, Panama mapped as Oligocene-Miocene. We studied, described, and identified two well-preserved specimens using wood anatomical characteristics and completed extensive comparisons between fossil and extant material. The studied fossil woods share several diagnostic features with the modern Anacardium genus, including large solitary vessels, large intervessel-pitting, a simple vessel-ray pitting pattern, and mostly 1–3 seriate rays with large rhomboidal solitary crystals. We propose a new fossil species named Anacardium gassonii sp. nov., that adds an essential piece to the understanding of the historical biogeography of the genus. In addition, our findings confirm previous interpretations of this species’ migration from Europe to North America and its crossing through Panama, leading to subsequent diversification in South America. This discovery provides an important link to the historical migration patterns of the genus, supporting the notion of an Eocene migration to the Neotropics via Boreotropical bridges, as well as an Oligocene-Miocene crossing of Central America followed by diversification in South America.

A new genus of Anacardiaceae based on wood from the Tepetate Formation (upper Eocene) of Baja California Sur, Mexico

“…The occurrence of this new genus of fossil wood from the upper Eocene of northern Mexico reinforces the hypo thesis that during the middle-late Eocene several biological and geological events occurred, such as the migration of some groups of plants to the Neotropics via Boreotropical bridges between the continents, which facilitated the dispersal of various groups of plants (Week et al 2014, Rodríguez-Reyes et al 2021. This Eocene biotic exchange between North America, Europe and Asia is documented by the fossil record of different plant families, e.g., Fabaceae (Martínez Millán 2000, Ramírez & Cevallos-Ferriz 2002, Estrada-Ruiz et al 2010, Pérez-Lara et al 2019.…”

“…Mangifera and Anacardium. Confer Mangifera axial parenchyma irregularly aliform with narrow wings, and radial canals are absent(Woodcock et al 2017) Rodríguez-Reyes et al (2021). reported the oldest Ana car dium-like fossil based on a fossil wood, but this wood differs from our woods in having indistinct growth rings and lacking radial canals.…”

“…has wider vessels, Several anacardiaceous fossil woods have been des cribed from different geological epochs in the world. Some features such as the occurrence of distinct growth ring boundaries, axial parenchyma pattern or ray composition, and radial canals, differ the two woods reported herein (e.g., Kruse 1954, Awasthi 1966, Poole & Davies 2001, Wheeler & Manchester 2002, Martínez-Cabrera & Cevallos-Ferriz 2004, Gregory et al 2009, Rodríguez-Reyes et al 2021. In Table 2 we compare the new genus fossil described herein with other selected taxa resulting from several searches in the IWD and a review of the wood anatomical literature.…”

“…Comparison between selected anacardiaceous fossil genera and the new two fossil woods from Baja California Sur (modified fromRodríguez- Reyes et al 2021). Terrazoxylon ductifera Wheeler et Manchester has indistinct growth rings, vessels solitary and in radial multiples of 2-6, and higher vessel frequency, exclusively septate fibers Woodcock et al (2017).…”