Cunoniaceae infructescences from the early Eocene Laguna del Hunco flora, Patagonia, Argentina

Abstract

Premise: Two distinct types of fossil infructescences from the early Eocene Laguna del Hunco flora, Chubut Province, Patagonia, Argentina, preserve features of the family Cunoniaceae. The goal of the study was to assess their affinities within Cunoniaceae and to interpret their evolutionary and biogeographical significance. Methods: Specimens were collected from the Tufolitas Laguna del Hunco, Huitrera Formation. They were prepared, photographed, and compared morphologically with similar extant and fossil fruits and infructescences using published literature and herbarium material. Results: The fruit and infructescence morphology place the fossil taxa within Cunoniaceae. They do not conform to any extant genus, supporting the erection of two new fossil genera. Racemofructus gen. nov. shares diagnostic features of the tribe Cunonieae, especially Weinmannia s.l., and exhibits two tribal morphological synapomorphies: a racemose inflorescence and a replum composed of a single column. Cunoniocarpa gen. nov. specimens are paniculate inflorescences with basipetally dehiscent, bicarpellate capsules that have persistent styles and calyces. Its replum morphology suggests an affinity to the tribe Caldcluvieae, particularly to the genus Ackama. Conclusions: The new Patagonian fossils described herein constitute the oldest record of cunoniaceous capsules globally, supplementing a significant body of fossil evidence from pollen, wood, and reproductive structures from southern South America and Antarctica that suggests that the Cunoniaceae were diversified and widely distributed in the southern hemisphere by the early Eocene. Racemofructus and Cunoniocarpa are, respectively, the first fossil records from South America of reproductive structures with affinity to tribes Cunonieae and Caldcluvieae.

The first Gondwanan Euphorbiaceae fossils reset the biogeographic history of the Macaranga‐Mallotus clade

“…Laguna del Hunco preserves an exceptional richness of living West Pacific rainforest taxa, and the occurrence of the MMC in the same strata aligns well with prior discoveries and the southern‐route‐to‐Asia scenario just discussed. Examples from Laguna del Hunco include the fern Todea (Osmundaceae); the cypress Papuacedrus ; the araucarian conifers Agathis and Araucaria Section Eutacta ; podocarpaceous conifers such as Dacrycarpus, Retrophyllum, Acmopyle , and an extinct relative of Phyllocladus ; and diverse angiosperms such as Castanopsis (Fagaceae), Eucalyptus (Myrtaceae), Gymnostoma (Casuarinaceae), Ceratopetalum and other Cunoniaceae, Akania (Akaniaceae), Ripogonum (Ripogonacae), engelhardioid Juglandaceae, and extinct relatives of Bubbia (Winteraceae), Wilkiea (Monimiaceae), and Daphnandra (Atherospermataceae) (Romero and Hickey, 1976; Zamaloa et al, 2006; Wilf et al, 2009, 2014, 2017a, 2019; Gandolfo et al, 2011; Wilf, 2012, 2020; Carvalho et al, 2013; Knight and Wilf, 2013; Carpenter et al, 2014; Hermsen and Gandolfo, 2016; Gandolfo and Hermsen, 2017; Andruchow‐Colombo et al, 2019; Rossetto‐Harris et al, 2020; Brea et al, 2021; Matel et al, 2022). The ranges of a majority of these lineages include the montane rainforests of New Guinea, where the MMC is highly diverse (Airy Shaw, 1980; Ashton, 2014).…”