248


Journal of Paleontology 92(2):240–253


symphyseal alveoli cannot be determined, but there are at least nine pairs. In lateral view, the mandible shows unclear sutures and therefore there is no way to determine the posterior limit of the dentary. The coronoid, visible in medial view, is partially covered by


the vomers. It projects anteriorly as an elongate sheet of bone that dorsally covers the medial surface of the mandible. The coronoid participates in the posterior part of the mandibular symphysis. No coronoid eminence is visible, probably because this area is damaged. The space between the coronoid eminence and the pos- teriormost alveolus is equivalent at least to the extension occupied by the posteriormost nine alveoli. The splenial is visible in ventral view where contact with the


coronoid is evident (Fig. 3). The anterior end of the splenial enters into the mandibular symphysis. Posterior to the symphysis, the splenial limits the ventral edge of the anterior Meckelian opening (Fig. 5.1). The angular is well preserved. The posterior part of this ele-


ment is not clearly distinguished because no sutures are visible, whereas the anterior part is visible clearly entering into the man- dibular symphysis (Fig. 3). The dorsal part of the surangular is not preserved, and the


sutures between the surangular and the coronoid are not clear. No lateral external concavity is observed in the preserved part. The suture with the prearticular is visible in medial view (Fig. 5.2). The prearticular is a blade-like bone that medially limits the Meckelian canal and forms part of the anterior limit of the posterior opening of the Meckelian canal. The articular forms the glenoid cavity and the retroarticular


process. The glenoid cavity is deep and transversely expanded facing medially. No lateral expansion of the glenoid area is observed (Fig. 2). The retroarticular process is short and robust with a rounded end. The glenoid cavity is located slightly below the alveolar line. Both hyoid elements are preserved. They are long, gracile and


gently curved (Fig. 3). Alveoli.—The anterior sector of the symphysis bears five


alveoli on the left side and four on the right side; the posterior- most alveoli are incomplete on both sides (Fig. 2). The ante- riormost pair of alveoli is smaller, circular, and cranially oriented. The second pair is larger than the first. The third, fourth, and fifth alveoli are even larger and posteromedially inclined (Fig. 4.5). In the posterior part of the mandibular symphysis, there are four alveoli on the right side and three on the left. Considering the lost part, at least nine symphyseal alveoli are present. There are 17 alveoli on the right mandibular ramus (post-symphysis), whereas the left mandibular ramus shows 15 alveoli, but it is incomplete. Therefore, the right mandible shows 26+ alveoli and the left 24+ alveoli. The interalveolar spaces are short, but those between the third and fourth and between the fourth and fifth alveoli are about half as long as the anteroposterior length of the fourth alveoli. Clear paradental plates are observed between the third and fourth pairs of alveoli (Fig. 4.6). Teeth.—There are no complete teeth, but several partially


preserved ones show a trihedral cross sections (Fig. 4.6, 4.7). The flat surface is labial and without striae. All of these features are observed in several teeth, but most clearly on the left fourth symphyseal tooth.


Postcranium.—The poorly preserved vertebral remains


comprise a posterior cervical centrum and several dorsal centra. The four limbs are preserved. The femora are larger than


the humeri (Fig. 5.4, 5.5). The right anterior limb is the best preserved (Fig. 5.5). The right humerus is preserved in two parts. The capitulum is convex as is the tubercle. Both capitulum and trochanter are almost completely confluent, but there is an anterior wide concave area between the capitulum and the trochanter on the posterior surface. The distal end shows two distal facets. The radial is short and widely rectangular (65mm long x 35mm wide). The ulna shows a posterior convex limit and two distal facets. The radial is also rectangular. The inter- medium is not well preserved. Distal carpal IV shows a proximal triangular end. Metacarpal V is completely shifted to the distal line. The distal carpal II +III is rectangular. Several phalanges are preserved (Fig. 5.5, 5.6). The femora are larger but more poorly preserved than the


humeri. The femoral capitulum is less circular than the humeral one. The distal end is expanded and similar to the humeral distal end (Fig. 5.4, 5.5).


Etymology.—After Cajón de Almanza, where MOZ 3728P, the holotype and only specimen, was collected.


Phylogenetic results.—The analysis recovered +20000 most parsimonious trees of 1338 steps (CI=0.294; RI=0.683). Pliosaurus almanzaensis n. sp. was recovered as part of a polytomy including other Pliosaurus species, the Brachauche- ninae Williston, 1925, and Gallardosaurus iturraldei Gasparini, 2009. This result is congruent with that obtained by Benson et al. (2013; Fig. 6.1). The IterPCR script identified the pliosaurid wildcard taxa Pliosaurus rossicus, DOKDM G/1–2, QM_F51291, Pliosaurus sp. (CAMSM J.35991), ‘P. irgisensis’ (Novozhilov, 1964), and P. patagonicus; these taxa were removed from the consensus and a reduced consensus was generated (Fig. 6.2). Pliosaurus almanzaensis n. sp. was recovered nested within the other Pliosurus species other than ‘P. andrewsi’ Tarlo, 1960 (Fig. 6.2). The monophyly of Pliosaurus in the reduced consensus is supported by character 139 (0-1): trihedral cross section of teeth.


Remarks.—To establish the validity of P. almanzaensis n. sp., it is compared with the other species of Pliosaurus. Pliosaurus brachydeirus and P. kevani have long alveolar lines: post- symphyseal alveoli (P. brachydeirus, 24; P. kevani, >22). Therefore, they differ from P. almanzaensis n. sp. with 15 or 16 post-symphyseal alveoli (Knutsen, 2012; Benson et al., 2013). Additionally, P. kevani has subtrihedrical teeth with only a slightly flattened labial surface that differs from P. almanzaensis n. sp. with trihedral teeth. The lateral surface of the mandible of P. kevani is concave (not observed in P. almanzaensis n. sp.) and the parasphenoid of P. kevani shows a sharp ventral keel that is absent in P. almanzaensis n. sp. Finally, the angular can be seen to penetrate into the symphysis in ventral view in both P. almanzaensis and P. kevani. Pliosaurus funkei Knutsen, Druckenmiller, and Hurum.,


2012, in which the number of symphyseal alveoli is unknown, has the interalveolar wall thicker than in P. almanzaensis n. sp. Additionally, P. funkei shows a ‘retroarticular fossa’ in the


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