Mosasaurus hoffmannii Mantell, 1829

Boles, Zachary M., Ullmann, Paul V., Putnam, Ian, Ford, Mariele & Deckhut, Joseph T., 2024, New vertebrate microfossils expand the diversity of the chondrichthyan and actinopterygian fauna of the Maastrichtian-Danian Hornerstown Formation in New Jersey, Acta Palaeontologica Polonica 69 (2), pp. 173-198 : 189

cf. Mosasaurus hoffmannii Mantell, 1829

Fig. 4D .

Material.—A nearly-complete right pterygoid (RU-EFP-03592) from the MFL, nine isolated teeth (RU-EFP-00109, 01826, 01901, 02703, 02916, and 00120-1–00120-4) and seven isolated vertebral centra (RU-EFP-00033, 02645, 03640, and 00043-1–00043-4) of mosasaurids have also been recovered from the MFL; many, if not all, of these specimens likely pertain to this same taxon, but they are too incomplete or lack enough diagnostic features for confident referral. All from Danian, Edelman Fossil Park, Mantua Township, New Jersey, USA.

Description.—The pterygoid is well preserved and represents one of the rarer skeletal elements of a mosasaurid recovered from the EFPQ in the last half century. Its preserved anteroposterior length is ~ 33 cm. Five erupted and three replacement teeth are present, although the specimen possesses a total of nine alveoli. The enamel of the preserved teeth is generally smooth or faintly faceted. Where these facets are present, they are much less well pronounced than in the marginal teeth of Mosasaurus hoffmannii . Faintly-serrated carinae are present on both the anterior and posterior margins of each tooth. As in other Mosasaurus species, the middle teeth are larger (crown height = 28 mm) than the posteriormost ones (~ 18 mm). As described for the holotype of M. hoffmannii by Street and Caldwell (2017), the tooth row is spindle shaped in ventral view with a rather flat parapet on the medial side and a bowed outwards parapet laterally. The basisphenoid and quadratic rami are each thin, with the quadratic ramus also being dorsomedially concave.

Remarks.—Several mosasaurs are known from Cretaceous strata in New Jersey, including the large-bodied taxa Mosasaurus conodon Cope, 1881 , M. hoffmannii , and Prognathodon rapax Hay, 1902 (see Gallagher 2005, 2015; Gallagher et al. 2012, for full taxa lists). Of these, M. cf. hoffmannii is known from the MFL whereas M. conodon and Prognathodon rapax are known from the underlying Navesink and Mount Laurel formations ( Gallagher 2005; Gallagher et al. 2012). RU-EFP-03592 differs from Prognathodon in having teeth with distinct facets ( Dortangs et al. 2002) and both anterior and posterior carinae ( Konishi et al. 2011). It also differs from M. conodon in having serrated carinae ( Ikejiri and Lucas 2015). The overall size and morphology of the pterygoid is consistent with that of M. hoffmannii ; although the only diagnostic feature reported for this species is the presence of eight teeth in the pterygoid ( Street and Caldwell 2017). However, other mosasaur genera have eight pterygoid teeth as well (e.g., M. conodon ), and tooth count can vary within mosasaurid genera or species ( Ikejiri and Lucas 2015). Given this uncertainty, we conservatively identify RU-EFP-03592 as belonging to cf. M. hoffmannii .

Mosasaur material is relatively rare in the MFL, being more common and more complete in the underlying formations ( Gallagher 2005, 2015; Gallagher et al. 2012). Within the MFL, typical finds include isolated teeth and worn centra. Thus, the recovery of a relatively complete and well-preserved pterygoid with teeth represents an exceptional discovery. These better-preserved specimens (RU-EFP-03592 and 00033, a large anterior?caudal retaining portions of the transverse processes and neural spine) also suggest that mosasaur material in the MFL is not reworked (contra Gallagher 1993, 2005).

Stratigraphic and geographic range.—Upper Cretaceous (Campanian to Maastricthtian) of Maryland, Missouri, New Jersey, South Dakota, Tennessee, and Texas in USA, Angola, Belgium, Brazil, Bulgaria, Canada, Denmark, Germany, Italy, Japan, Jordan, Morocco, Netherlands, New Zealand, Niger, Poland, Russia, South Africa, Spain, Syria, and Turkey.

Figures

Fig. 4. Remains of the alligatorid crocodilian Bottosaurus harlani (von Meyer, 1832) (A–C) and mosasaurid cf. Mosasaurus hoffmannii Mantell, 1829 (D) recovered from the Cretaceous–Paleogene lower Hornerstown Formation at the Jean and Ric Edelman Fossil Park in Mantua Township, New Jersey, USA. A. Posterior tooth (RU-EFP-02450) in labial (A1), lingual (A2), and mesial or distal (A3) views. B.?Posterior tooth (RU-EFP-03876) in labial (B1), lingual B2), and occlusal (B3) views. C. Left dentary (RU-EFP-03820) in dorsal (C1), medial (C2), lateral (C3), and ventral (C4) views. D. Right pterygoid (RU- EFP-03592) in medial (D1), ventral (D2), and lateral (D3) views.Abbreviations: av, alveolus; t, tooth.