Mystriosuchus, Fraas, 1896

Genus MYSTRIOSUCHUS Fraas, 1896 cf. Mystriosuchus alleroq López-Rojas et al. 2022

( Figure 6 View FIGURE 6 A-C)

Specimens referred. NHMD–1811690 – tooth; NHMD–1811691 – tooth; NHMD–1811841 – tooth; NHMD–1811842 – tooth; NHMD–1811843 – tooth; NHMD–1811844 – tooth; NHMD–1811845 – tooth; NHMD–1811846 – tooth; NHMD–1811847 – tooth; NHMD–1811848 – tooth; NHMD–1811850 – tooth; NHMD–1811851 – tooth; NHMD–1811852 – tooth; NHMD–1811853 – tooth; NHMD–1811854 – tooth; NHMD–1811855 – tooth; NHMD–1811856 – tooth; NHMD–1811857 – tooth; NHMD–1811858 – tooth.

Locality. From site 62/91/G, western side of Tait Bjerg , Jameson Land, East Greenland ( 71°28´34´´ North 22°40´43´´ West) GoogleMaps .

Horizon and age. Thin bone bed in Carlsberg Fjord Member of the Ørsted Dal Formation in the Fleming Fjord Group. Late Triassic (Norian).

Description. At least 19 isolated teeth have been identified as phytosaur teeth, including NHMD– 1811690 and NHMD–1811691. They are conical, slightly compressed labio-lingually on the carina, forming sharp edges on the mesial and distal margins. No strong curvature distally is visible for most teeth observed from this site because only the apical parts are present, except for NHMD–1811690 ( Figure 6A View FIGURE 6 ). The cross-section varies from Dshaped to oval-flattened, with strong edges slightly closer to the lingual side ( Figure 6B View FIGURE 6 ). Most preserved specimens consist only of the upper parts of teeth, shaped as an isosceles triangle in lingual or labial views with a long base. Due to bad preservation, apex is not always present, or only fragments of the crown are conserved. The size varies significantly between specimens; the largest tooth, NHMD–1811690, is 6 mm high and has a crown base of 8 mm long and 5 mm wide. NHMD– 1811691 is a bit smaller, 5 mm high with a crown base of 4.5 mm long and 2 mm wide. Few specimens preserved their serrated carinae. NHMD– 1811691 possesses serration on a 1.5 mm mesial margin towards the crown apex. Even though the denticles are complicated to distinguish as there is no clear separation, the preserved denticles are domed-shaped and wider than high ( Figure 6C View FIGURE 6 ).

Remarks. The teeth of phytosaurs have already been mentioned in Tait Bjerg (Jenkins et al., 1994) but were barely described back then. Then, another specimen has been described but without teeth associated to the material (Mateus et al., 2014). Today, specimens observed here can be compared to Mystriosuchus alleroq , a phytosaur recently described in the Jameson Land Basin (López-Rojas et al., 2022), whose heterodont teeth have been studied. However, the specimens in this study are poorly preserved, preventing us from pushing further the description (e.g., serration density). Thus, NHMD–1811690 could be assigned to the posterior maxilla region due to its rather flattened and stocky appearance and oval cross-sections. It is more difficult to determine the anatomical tooth position of NHMD–1811691 since an important part from the middle crown to the base is missing. However, from its slightly Dshaped cross-section and straight lingual and labial faces, it could be assigned to the posterior premaxilla set. Still, based on their morphology and the recently described M. alleroq , these teeth are tentatively assigned to this species considering the anatomy and geographical and geological context. Because of the absence of diagnostic tooth characters, we can only assign them to cf. M. alleroq .