Journal of Paleontology, 92(2), 2018, p. 240–253 Copyright © 2018, The Paleontological Society 0022-3360/18/0088-0906 doi: 10.1017/jpa.2017.82


A new Pliosaurus species (Sauropterygia, Plesiosauria) from the Upper Jurassic of Patagonia: new insights on the Tithonian morphological disparity of mandibular symphyseal morphology


José P. O’Gorman,1,2 Zulma Gasparini,1,2 and Luis A. Spalletti2,3


1División Paleontología Vertebrados, Museo de La Plata, Universidad Nacional de La Plata, Paseo del Bosque s/n., B1900FWA, La Plata, Argentina 2CONICET: Consejo Nacional de Investigaciones Científicas y Técnicas, Ciudad Autonoma de Buenos Aires, Argentina ⟨joseogorman@fcnym.


unlp.edu.ar⟩; ⟨zgaspari@fcnym.unlp.edu.ar⟩ 3Centro de Investigaciones Geológicas, Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, La Plata, Argentina ⟨spalle@cig.museo.unlp.edu.ar⟩


Abstract.—Most species of the genus Pliosaurus Owen, 1842 come from the Northern Hemisphere, however, a growing number of new specimens are now available from the Southern Hemisphere. Here, a new species of Pliosaurus is described, the second for the genus from the Southern Hemisphere, collected from the upper Tithonian (Jurassic) levels of the Vaca Muerta Formation, Neuquén Province, Patagonia. Pliosaurus almanzaensis new species is characterized by two autapomophies: the angular participating in the mandibular symphysis and the occipital condyle without a notochordal pit or several, irregularly arranged grooves. Additionally, P. almanzaensis n. sp. can be differentiated from other Pliosaurus species by the following characters: trihedral teeth, nine or more symphyseal alveoli, 15–17 post-symphyseal alveoli, and the parasphenoid without a ventral keel. Pliosaurus almanzaensis n. sp. shows that Pliosaurus species with nine or more symphyseal alveoli persisted until the late Tithonian, contrary to previous assumptions that only species with six symphyseal alveoli were present.


Introduction


Pliosaurid plesiosaurs (sensu Benson and Druckenmiller, 2014) were Mesozoic macropredator sauropterygians that evolved a short neck and relatively large skull condition (Sassoon et al., 2012; Benson et al., 2013; Fischer et al., 2015). Pliosaurids had a global distribution and their biochron spans from the Early Jurassic to the early Late Cretaceous (Kear, 2012; Sasoon et al., 2012; Benson et al., 2013; Benson and Druckenmiller, 2014; Fischer et al., 2015; Páramo-Fonseca et al., 2016). Despite this long record, the best-known species come


mostly from European Oxfordian and Kimmeridgian deposits (Benson et al., 2013). However, new records have recently improved the knowledge of pliosaurids from other Jurassic localities such as Spitsbergen (Knutsen et al., 2012), Mexico (Buchy et al., 2003; Barrientos-Lara et al., 2015), and Patagonian Argentina (Gasparini and O’Gorman, 2014) as well as the Lower Cretaceous of the USA (Albright et al., 2007; Schumacher et al., 2013), Colombia (Hampe, 2005; Páramo-Fonseca et al., 2016), and Australia (Benson et al., 2013). At the same time, new phy- logenetic analyses based on the revision of classic taxa, including the genus Pliosaurus Owen, 1842 and new specimens, have improved the knowledge of the relationships among pliosaurids (O’Keefe, 2001; Ketchum and Benson, 2010; Knutsen et al., 2012; Sassoon et al., 2012; Benson and Druckenmiller, 2014). Additionally, morphofunctional aspects of pliosaurids have recently been discussed (Foffa et al., 2014a, b).


and Benson et al. (2013) is clarification of the classic problemof definition of the genus Pliosaurus (previously discussed by Tarlo, 1960 and Noè et al., 2004). These last revisions agreed in the validity and definition of Pliosaurus although with differ- ences regarding the validity of some species. The general con- clusions of these authors are followed in this contribution. Argentine pliosaurids come fromtheVacaMuerta Formation,


One of the main results of the revisions of Knutsen (2012)


Neuquén, from the middle Tithonian (Pliosaurus patagonicus Gasparini and O’Gorman, 2014) and late Tithonian (Gasparini et al., 1997; this study). At the beginning of 1986, the brothers Sergio and Rafael Cocca, technicians of the Museo Provincial de Ciencias Naturales Prof. Dr. Juan A. Olsacher de Zapala,Neuquén Province, Argentina (MOZ), discovered part of a pliosaur post- cranium in Cajón de Almanza, 10km east of Loncopué village, in west-central Neuquén Province (Fig. 1). A subsequent field trip (1986) was carried out with theMOZstaff and ZGto determine the possible position of the skull. In February 1987, the MOZ staff collected the entire specimen (MOZ 3728P) and in January 1988 one of the authors (L.S.) determined the exact stratigraphic position of the specimen. The main objective of this contribution is to describe


MOZ 3728P, the holotype and only specimen of Pliosaurus almanzaensis new species from the upper Tithonian levels of the Vaca Muerta Formation, Patagonia. Pliosaurus almanzaensis n. sp., along with P. patagonicus, are the only Pliosaurus species from Gondwana.


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