Pleistocene record of <i>Chloephaga</i> Eyton, 1838 (Anseriformes: Anatidae) in the Argentine Pampas, with the description of a new species

The genus Chloephaga Eyton, 1838, consisting of four species that breed in Patagonia, encompasses anatids endemic to South America. Despite their prominence in the present-day avifauna, these species have left behind a limited fossil record. The aim of the present contribution is to describe Chloephaga fossils coming from Middle Pleistocene levels (San Jos&eacute; Sequence) cropping out at Bajo San Jos&eacute; site, southwestern Buenos Aires Province, Argentina. The specimens are referred to three different taxa, including a new species, Chloephaga dabbenei n. sp., a smaller but indeterminate taxon, which is also probably a new species, and the extant species C. picta (J.F.Gmelin, 1789). The newly described species is notably large, falling within the upper size range observed in males of C. picta. The tarsometatarsus is straight-shafted with poorly divergent distal trochleae, features that are correlated with cursorial habits, that are absent in other members of Chloephaga. The co-occurrence of three species of the genus Chloephaga is registered nowadays in the Argentine Patagonia and in the southeast of Buenos Aires Province, when they migrate during the winter season.草雁属（Chloephaga Eyton, 1838）由4种繁殖于巴塔哥尼亚的物种组成，为南美洲特有的鸭科类群。尽管该属物种在现今鸟类区系中占据重要地位，但其化石记录却十分匮乏。本研究旨在描述采自阿根廷布宜诺斯艾利斯省西南部巴霍圣何塞遗址出露的中更新统圣何塞层序的草雁属化石。本次研究的标本归入3个不同的分类群：包括新种达氏草雁（Chloephaga dabbenei n. sp.）、体型更小且分类未定、大概率亦为新种的类群，以及现生种白草雁（C. picta，J.F.Gmelin, 1789）。本次描述的新种体型显著偏大，其体型范围处于白草雁雄性个体的最大尺寸区间内。该新种的跗跖骨（tarsometatarsus）骨轴笔直，远端滑车发散程度较弱，这些特征与奔跑习性相关，而为草雁属其他成员所不具备。如今，草雁属3个物种的同域分布现象见于阿根廷巴塔哥尼亚及布宜诺斯艾利斯省东南部，此时它们正处于冬季迁徙期。