Rare evidence of a giant pliosaurid-like plesiosaur from the Middle Jurassic (lower Bajocian) of Switzerland
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REGULAR RESEARCH ARTICLE
Rare evidence of a giant pliosaurid-like plesiosaur from the Middle Jurassic (lower Bajocian) of Switzerland Sven Sachs1,2
•
Christian Klug3 • Benjamin P. Kear4
Received: 23 August 2019 / Accepted: 15 October 2019 Ó Akademie der Naturwissenschaften Schweiz (SCNAT) 2019
Abstract Here, we describe part of a large-bodied macrophagous plesiosaur jaw from the lower Bajocian (Middle Jurassic) Passwang Formation near Arisdorf in the Basel-Land canton of Switzerland. The specimen preserves the posterior glenoid extremity of the right mandibular ramus comprising the surangular, angular, articular, and probably the prearticular. Notable character states include a transversely expanded surangular that incorporates a prominent medial ridge adjacent to the glenoid and a shallow dorsal fossa, together with a conspicuous trough extending across the lateral surfaces of both the surangular and angular; there is also a basally broad and medially deflected retroarticular process. Collectively, these features suggest affinities with Middle–Late Jurassic pliosaurids, as well as some coeval rhomaleosaurids. Based on such comparisons, we estimate that the Passwang Formation mandible was approximately 1.5 m long when complete, and thus approaches the size range of the largest-known pliosaurids. This discovery supplements the sparse record of diagnostic pliosaurid-like remains from Switzerland and contributes to the currently incomplete knowledge of pre-Callovian Middle Jurassic plesiosaurs globally. Keywords Plesiosauria Pliosauromorph Pliosauridae Rhomaleosauridae Bajocian Apex predator
Introduction Although both geographically and stratigraphically ubiquitous, the fossil record of plesiosaurs currently has very incomplete representation from Middle Jurassic strata of pre-Callovian (Aalenian–Bajocian) age (e.g. Buchy 2004; Gasparini 1997; Gasparini and Ferna´ndez 2006; Godefroit 1994; Kear 2012; Sachs and Hornung 2016; Vincent et al. 2007, 2013b). To date, only two taxa have been recognised from this interval: the rhomaleosaurid Maresaurus coccai
Editorial Handling: D. Marty. & Sven Sachs [email protected] 1
Naturkunde-Museum Bielefeld, Abteilung Geowissenschaften, Adenauerplatz 2, 33602 Bielefeld, Germany
2
Im Hof 9, 51766 Engelskirchen, Germany
3
Pala¨ontologisches Institut und Museum, University of Zurich, Karl Schmid-Strasse 4, 8006 Zurich, Switzerland
4
Museum of Evolution, Uppsala University, Norbyva¨gen 16, 752 36 Uppsala, Sweden
(Gasparini 1997), from the early Bajocian of Argentina, and the probable pliosaurid Simolestes keileni (Godefroit 1994) from the late Bajocian of France. Consequently, the understanding of early Middle Jurassic plesiosaur diversity and distribution is, at present, extremely limited (e.g. Bardet et al. 2014; Kear et al. 2018; Tutin and Butler 2017). Here, we briefly report the discovery of an incomplete mandible representing a large-skulled pliosaurid-like plesiosaur from the lower Bajocian section of the Pass
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