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

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.

Cretaceous–Paleogene plant extinction and recovery in Patagonia

“…3D–G) belongs to the family Rosaceae based on diagnostic characters including serrated margins with compound teeth and craspedodromous secondary venation. The survivorship of the family Rosaceae is a new contribution of this study, along with Cretaceous macrofloral evidence to support the K/Pg survival of Malvaceae and Cunoniaceae, previously known from pollen records in these sections (Barreda et al 2012; Jud et al 2018a,b).…”

“…Gymnosperm macrofossils of the Lefipán and Salamanca Formations have been the subject of taxonomic studies (Zamuner et al 2000; Brea et al 2005; Quiroga et al 2015; Ruiz et al 2017; Wilf et al 2017; Andruchow-Colombo et al 2018, 2019; Escapa et al 2018), indicating the survival of the Podocarpaceae and Araucariaceae conifer families. The presence of several derived angiosperm groups known from reproductive material in the Salamanca Formation suggests that they also represent K/Pg survivor families (Iglesias et al 2007; Raigemborn et al 2009; Jud et al 2017, 2018a,b; Supplementary Tables 1, 2). Angiosperm leaf fossils have sourced the aforementioned work on K/Pg insect damage (Donovan et al 2016, 2018), yet the extensive leaf collections on which the insect herbivory was documented have not been rigorously compared to quantify macrofloral species extinction in Patagonia across the Cretaceous/Paleogene transition.…”

Agathistrees of Patagonia's Cretaceous‐Paleogene death landscapes and their evolutionary significance

“…The PL exposures have been known for ca. 80 years from their well‐preserved fossil plants (see Berry, ; Feruglio, ), including fossil woods (e.g., Brea et al., , Ruiz et al., ), and have been the topic of several recent investigations (Iglesias et al., ; Brea et al., ; Clyde et al., ; Comer et al., ; Donovan et al., ; Jud et al., ). The fossils reported here all come from the PL‐2 quarry of Iglesias et al.…”

Seed traits linked to differential survival of plants during the Cretaceous/Paleogene impact winter

“…Overprinted on this general pattern of recovery is recolonization of South America by orthodox seed-producing Nothofagus from Antarctica (Leppe et al, 2012;Jud et al, 2018;Romero et al, 2019). Climate models clearly indicate that the polar regions offered no climatic refugia for the mature forms of such plants (Chiarenza et al, 2020), so it is clear from the present data that these plants must have recovered from a seed bank.…”