Fossil flowers from the early Palaeocene of Patagonia, Argentina, with affinity to Schizomerieae (Cunoniaceae).

Peter Wilf,Ari Iglesias,Nathan A Jud,Maria A Gandolfo

doi:10.1093/aob/mcx173

Abstract

Background and AimsEarly Palaeocene (Danian) plant fossils from Patagonia provide information on the recovery from the end-Cretaceous extinction and Cenozoic floristic change in South America. Actinomorphic flowers with eight to ten perianth parts are described and evaluated in a phylogenetic framework. The goal of this study is to determine the identity of these fossil flowers and to discuss their evolutionary, palaeoecological and biogeographical significanceMethodsMore than 100 fossilized flowers were collected from three localities in the Danian Salamanca and Peñas Coloradas Formations in southern Chubut. They were prepared, photographed and compared with similar extant and fossil flowers using published literature and herbarium specimens. Phylogenetic analysis was performed using morphological and molecular data.Key resultsThe fossil flowers share some but not all the synapomorphies that characterize the Schizomerieae, a tribe within Cunoniaceae. These features include the shallow floral cup, variable number of perianth parts arranged in two whorls, laciniate petals, anthers with a connective extension, and a superior ovary with free styles. The number of perianth parts is doubled and the in situ pollen is tricolporate, with a surface more like that of other Cunoniaceae outside Schizomerieae, such as Davidsonia or Weinmannia.ConclusionsAn extinct genus of crown-group Cunoniaceae is recognized and placed along the stem lineage leading to Schizomerieae. Extant relatives are typical of tropical to southern-temperate rainforests, and these fossils likely indicate a similarly warm and wet temperate palaeoclimate. The oldest reliable occurrences of the family are fossil pollen and wood from the Upper Cretaceous of the Antarctica and Argentina, whereas in Australia the family first occurs in upper Palaeocene deposits. This discovery demonstrates that the family survived the Cretaceous–Palaeogene boundary event in Patagonia and that diversification of extant lineages in the family was under way by the earliest Cenozoic.

Highlights

IntroductionThe lower Palaeocene (Danian) deposits that crop out in central Patagonia, Argentina, yield exquisitely preserved plant remains (Berry, 1937; Romero, 1968; Petriella, 1972; Archangelsky, 1973; Petriella and Archangelsky, 1975; Archangelsky and Zamaloa, 1986; Brea et al, 2005, 2008; Iglesias et al, 2007; Barreda et al, 2012; Futey et al, 2012; Donovan et al, 2016; Ruiz et al, 2017)
In addition to the holotype and 11 paratype specimens figured here, we examined a total of 99 other specimens from Palacio de los Loros-2 (PL-2) and three from Palacio de los Loros-5 (PL-5) in the Salamanca Formation (C28n, early Palaeocene) and one from the Las Flores (LF) locality in the Peñas Coloradas Formation (C27n, early Palaeocene)
Because of the differences between the two species, we suggest that a critical evaluation of the phylogenetic position of these species requires their inclusion in a broad phylogenetic analysis of rosid floral characteristics, a task that is beyond the scope of this work

Summary

Introduction

The lower Palaeocene (Danian) deposits that crop out in central Patagonia, Argentina, yield exquisitely preserved plant remains (Berry, 1937; Romero, 1968; Petriella, 1972; Archangelsky, 1973; Petriella and Archangelsky, 1975; Archangelsky and Zamaloa, 1986; Brea et al, 2005, 2008; Iglesias et al, 2007; Barreda et al, 2012; Futey et al, 2012; Donovan et al, 2016; Ruiz et al, 2017) These fossils provide some of the oldest reliable Danian records of taxa that survived the end-Cretaceous extinction event in the Southern Hemisphere. The family was extirpated from Antarctica sometime after the middle Eocene (Cranwell, 1959; Askin, 1997; Cantrill and Poole, 2012; Tosolini et al, 2013) but persisted in South America, Africa and Australia, spreading to Central America and Indomalesia (Bradford et al, 2004)

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