Data from: Fruits of Juglandaceae from the Eocene of South America

Specimens of a new fruit taxon, Alatonucula ignis, from the early Eocene Laguna del Hunco flora of Chubut, Patagonia, Argentina, have characteristics consistent with assignment to Juglandaceae. Each fossil fruit consists of a nutlet with an attached wing that varies from unlobed to trilobed. One specimen clearly shows that the nutlet has a single locule partially subdivided into four chambers; its counterpart contains a four-lobed locule cast. The basally partitioned locule with lobed seed indicates that Alatonucula can be placed within Juglandaceae; the overall structure of the fruits suggests affinities to subfamily Engelhardioideae, which typically have fruits consisting of a nutlet attached to a trilobed wing. Parsimony analyses of a morphological matrix for extant and fossil Juglandaceae revised from a previously published study demonstrate that 1) Alatonucula groups with Engelhardioideae; and 2) Paleooreomunnea, an Eocene North American taxon that includes a fruit type with a trilobed wing, is within crown-group Engelhardioideae. Alatonucula, along with fossil juglandaceous pollen from the Paleogene of Patagonia, indicates that Juglandaceae may have had an unexpectedly early presence in South America. Furthermore, these fruits represent a Laurasian biogeographic signal in the Laguna del Hunco flora, which contrasts with the predominantly Australasian signal highlighted in previous studies.采自阿根廷巴塔哥尼亚丘布特省始新世早期拉古纳德尔翁科（Laguna del Hunco）植物群的新果类群Alatonucula ignis标本，其形态特征与胡桃科（Juglandaceae）的归属判定标准相符。每件化石果实均由一枚附着有翅的小坚果构成，翅的形态从全缘到三裂不等。其中一件标本清晰显示，该小坚果具1个子房室，局部被分隔为4个腔室；其对开标本的另一面则保存有四裂的室腔铸型。基部具分隔的室腔与带裂片的种子特征表明，Alatonucula可归入胡桃科（Juglandaceae）；果实的整体结构则显示其与黄杞亚科（Engelhardioideae）存在密切亲缘关系，该亚科的果实通常由附着有三裂翅的小坚果组成。基于此前已发表研究修订的现生与化石胡桃科形态矩阵所开展的简约性分析结果显示：1) Alatonucula与黄杞亚科聚为一支；2) 北美始新世类群古奥雷蒙尼亚木属（Paleooreomunnea，其类群包含具三裂翅的果实类型）隶属于冠群黄杞亚科。Alatonucula连同巴塔哥尼亚古近纪产出的胡桃科花粉化石，表明胡桃科（Juglandaceae）在南美洲的出现时间可能远超此前预期。此外，这些果实化石为拉古纳德尔翁科植物群带来了劳亚大陆生物地理信号，这与此前研究中强调的该植物群以澳大拉西亚生物地理信号为主的结论形成鲜明对比。