New Paleocene bird fossils from the North Sea Basin in Belgium and France

1. Introduction Europe has a comparatively rich and well-studied Eocene avian fossil record, but bird remains from the Paleocene period are very scant (Mayr, 2009, 2017a, b; Mayr et al., 2019a). The exact age of some localities is furthermore controversially discussed, which impedes well-founded biogeographic inferences. The Paleocene is divided into three stages, the Danian (66.0‒61.6 million years ago [Ma]), Selandian (61.6‒59.2 Ma), and Thanetian (59.2‒56.0 Ma). With the exception of Scaniornis lundgreni from the Danian of Sweden ‒ a bird of uncertain phylogenetic affinities that is only known from the poorly preserved wing bones of the holotype (Dames, 1890) ‒, all bird fossils from the Paleocene of Europe stem from the Selandian and Thanetian stages. Already in the 19th century, fossils of the large flightless Gastornithidae were described from the late Thanetian (~57.5 Ma) localities Cernay-les-Reims and Mont-de-Berru in the eastern Paris Basin in France (Lemoine, 1878, 1881; Martin, 1992; Buffetaut, 1997; Mourer-Chauvire & Bourdon, 2016). Equally long known from these sites is the palaeognathous taxon Remiornis, whereas the description of other avian remains from the Mont-de-Berru area commenced much later (Mourer-Chauvire, 1994, 1995). This is also true for bird fossils from the fissure fillings of Walbeck in Germany, which were found in the first half of the 20th century, but have been described more than 70 years later (Mayr, 2002a, 2007). Even on a global scale