O’Gorman et al.—A new pliosaurid from Patagonia


other pliosauroids (Gasparini, 2009; Benson et al., 2011, 2013). The presence of a deep notch in the posterior margin of the dorsal surface of the body of the basisphenoid [‘clivus’]as observed in P. almanzaensis n. sp. is present in some pliosaurids such as Peloneustes Lydekker, 1889 and Liopleurodon Sauvage, 1873 (Benson and Druckenmiller, 2014), but is difficult to assess among the Brachaucheninae and other Pliosaurus spp. because the dorsal surface of basisphenoid is usually covered in most-complete specimens. The parasphenoid shows the plesiomorphic triangular


condition observed in other pliosaurids (O’Keefe, 2001), however, the morphology of the posterior end of the parasphenoid varies


Table 1. Valid species of Pliosaurus (following Knutsen et al., 2012, Benson et al., 2013, and Gasparini and O’Gorman, 2014).


Species


Pliosaurus almanzaensis n. sp. Pliosaurus brachydeirus Owen, 1841


Pliosaurus carpenteri Benson et al., 2013 Pliosaurus kevani Benson et al., 2013


Pliosaurus funkei Knutsen, Druckenmiller and Hurum, 2012


Pliosaurus patagonicus Gasparini and O’Gorman, 2014


Pliosaurus rossicus Novozhilov, 1948 Stratigraphic provenance


upper Tithonian, Patagonia lower Kimmeridgian, England


upper Kimmeridgian, England


lower Kimmeridgian, England


middle Volgian, Svalbard, Norway


Pliosaurus westburyensis Benson et al., 2013 upper Kimmeridgian, England


middle Tithonian, Argentina Tithonian, Russia


251


among pliosaurids. Some of them, such as Rhomaleosaurus cramptoni (Carte and Baily, 1863) and Peloneustes philarchus Seeley, 1869, show a short parasphenoid not ventrally covering the basioccipital in the midline (Smith and Dyke, 2008; Ketchum and Benson, 2011). In contrast, among species of Pliosaurus,in P. kevani, the parasphenoid reaches the level of the basioccipital (Benson et al., 2013).Additionally, in P. kevani, the parasphenoid has a posterior notch (Benson et al., 2013, fig. 5), and in P. almanzaensis n. sp., there is a small depression in the posteriormost visible area of the parasphenoid. Therefore, the posterior notch, similar to that of P. kevani, is probably present although it is mostly covered by the posterior interpterygoid symphysis. The rugose surface of the basisphenoid has been mentioned for Peloneustes philarchus (see O’Keefe, 2001), suggesting a poor state of ossification. The same feature in Pliosaurus almanzaensis n. sp. reinforces the observation of O’Keefe (2001) about poor ossification of the basisphenoid in pliosaurids. The sella turcica of Pliosaurus almanzaensis n. sp. is located in a caudoventrally directed depression, differing fromthe caudally directed depression recorded in several Plesiosauroidea such as Brancasaurus brancaiWegner, 1914, Dolichorhynchops Williston, 1902 (see Sato et al., 2011), and Alexandronectes zealandiensis Otero et al., 2016.


Symphyseal alveolar account and morphological disparity.— According to Knutsen (2012), the Upper Jurassic species of Pliosaurus ranging from the Kimmeridgian to the Tithonian


Figure 7. Plot of symphyseal alveoli number and stratigraphic position of various Pliosaurus species. Data from Benson et al. (2013) and Gasparini and O’Gorman (2014).


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