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1.
Introduction
The Plesiosauria are a group of large marine predators known from latest Triassic to the end of Late Cretaceous time, when they become extinct during the biological crisis of the Cretaceous-Palaeogene (K-Pg) boundary (e.g. Vincent et al. 2011). Soon after their first appearance in the fossil record at the end of Triassic time, they underwent a spectacular radiation and became widespread both in time and space, being highly systematically and ecologically diversified throughout the Jurassic-Cretaceous periods and found in all continents (Ketchum & Benson, 2010).
During Late Cretaceous time the Plesiosauria were particularly diversified and mainly represented by Plesiosauroidea, known by the three families Elasmosauridae, Polycotylidae and Leptocleididae, as well as by the declining Pliosauroidea, known by the Pliosauridae only (Ketchum & Benson, 2010). Cretaceous pliosaurs are only represented by: Kronosaurus Longman, 1924 from Aptian-Albian Australia and Colombia; Brachauchenius Williston, 1903 from the Turonian Western Interior Seaway and Barremian Colombia (Hampe, 2005); and Megacephalosaurus eulerti Schumacher, Carpenter & Everhart, 2013 (FHSM VP321) and Schumacher, 2008 (paratype UNSM 50136) from Turonian Kansas (see Ketchum & Benson, 2010 for details, and online Supplementary Material Table S3 available at http://journals.cambridge.org/geo).
Compared to other continents, the fossil record of plesiosaurs is scarce in Africa where only five valid taxa are known. All described from Cretaceous outcrops, these are: the leptocleidid Leptocleidus capensis (Andrews, 1911) from Early Cretaceous (Valanginian) South Africa (Andrews, 1911; Cruickshank, 1997); the elasmosaurid Zarafasaura oceanis Vincent et al. 2011 from latest Cretaceous (Maastrichtian) Morocco (Vincent et al. 2011); and the polycotylids Thililua longicollis Bardet, Suberbiola & Jalil, 2003a and Manemergus anguirostris Buchy, Metayer & Frey, 2005 and the elasmosaurid Libonectes atlasense Buchy, 2005 described from the lower Upper Cretaceous (Turonian) sediments of the Goulmima outcrop, southern Morocco (Bardet, Suberbiola & Jalil, 2003a ; Buchy, 2005; Buchy, Metayer & Frey, 2005).
The Goulmima outcrop today represents the richest plesiosaur site from Africa, with the two major clades of Cretaceous plesiosaurs represented as well as the elasmosaurids and the polycotylids. Here we describe a new plesiosaur specimen from this outcrop belonging to the Pliosauridae, a clade previously undescribed from this area.
Abbreviations: FHSM - The Sternberg Museum of Natural History, Hays, Kansas (USA); MNHN - Muséum National d'Histoire Naturelle, Paris (France); UNSM...