Mosasaurid and plesiosaurian remains from marginal facies of the lower Campanian (Upper Cretaceous) Bottrop and Vaals formations of western Germany Sven Sachs a, b,* , Jahn J. Hornung c , Udo Scheer d a Naturkundemuseum Bielefeld, Abteilung Geowissenschaften, Adenauerplatz 2, 33602 Bielefeld, Germany b Im Hof 9, 51766 Engelskirchen, Germany c Fuhlsbüttler Straße 611, 22337 Hamburg, Germany d Stiftung Ruhr Museum, Fritz-Schupp-Allee 15, 45141 Essen, Germany * Corresponding author. E-mail addresses: Sachs.Pal@gmail.com (S. Sachs), jahn.hornung@yahoo.de (J.J. Hornung), udo.scheer@ruhrmuseum.de (U. Scheer). A B S T R A C T Isolated remains of mosasaurids and plesiosaurians are recorded from the lower Campanian Bottrop and Vaals formations of North Rhine-Westphalia, western Germany. A tooth crown from Bottrop- Fuhlenbrock, referred to an elasmosaurid plesiosaurian, represents the first record of this group from late-Upper Cretaceous strata of the area. Another presumed plesiosaurian remain is a fragmentary gastralium from Duisburg-Walsum. Some of the mosasaurid material from the Bottrop Formation (a tooth crown and vertebrae from Bottrop-Fuhlenbrock and Duisburg-Walsum) is assigned to the subfamily Plioplatecarpinae. The Vaals Formation, which is a lateral equivalent of the Bottrop Formation, yielded a single tooth crown, found at Aachen-Bildchen, that is here referred to the genus Hainosaurus. These finds from the Bottrop and Vaals formations constitute evidence of the presence of these taxa in proximal shelf to nearshore settings during the Campanian. The mosasaurid occurrences in particular may be an indicator that diversity and abundance increased in more basinward facies and greater palaeowaterdepth. 1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28