Integrative identification of a Paleogene Acer samara from southwestern China using geometric morphometrics and diagnostic morphology

Abstract

Acer samaras are widely reported from Cenozoic deposits of the Northern Hemisphere, yet species-level identification remains challenging because traditional dichotomous characters poorly capture subtle, continuous morphological variation. Here, we integrate geometric morphometrics with diagnostic morphology to evaluate an Eocene fossil samara from southwestern China. Comparative datasets comprised 276 samaras representing 28 representative extant taxa from southern Asia and 67 published fossil specimens representing 44 species. We assessed the performance of the morphometric approach using leave-one-out pseudo-fossil validation, in which each extant specimen was treated as an unknown and classified against the remaining reference dataset. Across the principal component analysis (PCA)- and canonical variate analysis (CVA)-based procedures, recovery was consistently higher in CVA space, where the correct taxon was ranked first in 68% of cases, within the Top-5 in 95%, and within the Top-10 in 99%, showing that geometric morphometrics is effective for narrowing candidate taxa. Applied to the Maguan fossil, PCA and CVA each identified 10 morphometrically closest extant taxa, with Acer sterculiaceum subsp. franchetii , A. oblongum , and A. paxii among the highest-ranked candidates. Traditional morphology showed that all ten differed from the Maguan fossil in nutlet morphology, venation, or wing-vein architecture; none matched its diagnostic character combination. Among the fossil species, A. wehri , although morphometrically similar, differs markedly in venation, supporting the designation of the Maguan fossil as a new species, A. maguanense sp. nov. Our fossil adds a Paleogene record of Acer in southern East Asia and highlights the value of combining quantitative shape screening with diagnostic morphology for fossil identification.

The authors' abstract, as published at the source. Review of Palaeobotany and Palynology, 2026 · DOI ↗