Gerrothorax pulcherrimus (Fraas, 1913)

Gerrothorax pulcherrimus (Fraas, 1913)

( Figure 5A View FIGURE 5 )

Specimens referred. NHMD–1811685 – ornamented skull fragment; NHMD–1811821 – ornamented skull fragment.

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. Bone fragment with tubercular ornamentation. The tubercules are conical structures with smooth surfaces.

Remarks. The bone lacks any anatomical feature other than the tubercular ornamentation necessary to identify it. This type of ornamentation is typical of the dermal bone of the skull of Plagiosaurinae since similar ornamentation has been noted in Gerrothorax pulcherrimus , notably the skull, the mandible, and the pectoral girdle, with the other members of Plagiosaurinae Abel, 1919 (Jenkins et al., 2008). However, it displays more prominent tubercles (pustular), as can be seen in several specimens used to reconstruct the skull of G. pulcherrimus (e.g., MGUH 28923 and MGUH 28925 in Jenkins et al., 2008). Of all temnospondyl remains of Greenland, only Gerrothorax displays such ornamentation (Jenkins et al., 1994). In addition, the context of age and location of the specimen is consistent with previous discoveries of the species in three other localities in the basin: MacKnight Bjerg, Sydkronen, and Lepidopteriselv (Jenkins et al., 1994; Marzola et al., 2018). Considering the pustular aspect of the ornamentation, without any continuous ridges, NHMD–1811685 could belong to a large specimen (Schoch and Witzmann, 2011).

Temnospondyli indet.

( Figure 5 View FIGURE 5 B-G)

Specimens referred. NHMD–1811686 – tooth; NHMD–1811687 – dentary; NHMD–1811688 – tooth; NHMD–1811822 – tooth; NHMD–1811823 – tooth; NHMD–1811824 – tooth; NHMD–1811825 – tooth; NHMD–1811826 – tooth; NHMD–1811827 – tooth; NHMD–1811828 – tooth; NHMD–1811829 – tooth; NHMD–1811830 – tooth; NHMD–1811831 – tooth; NHMD–1811832 – tooth; NHMD–1811833 – tooth; NHMD–1811834 – tooth; NHMD–1811835 –

tooth; NHMD–1811836 – tooth; NHMD–1811837 –

tooth; NHMD–1811838 – tooth; NHMD–1811839 –

tooth; NHMD–1811840 – maxilla.

Locality. From site 62/91/G, western side of Tait

Bjerg, Jameson Land, East Greenland (71°28´34´´

North 22°40´43´´ West).

Horizon and age. Thin bone bed in Carlsberg

Fjord Member of the Ørsted Dal Formation in the

Fleming Fjord Group. Late Triassic (Norian).

Description. More than 20 temnospondyl remains are reported here. Most of these remains are teeth and two jaw fragments that are too poorly preserved for further identification.

Jaw fragments ( Figure 5 View FIGURE 5 B-C): There are two jaw fragments. The first, NHMD–1811687 is a dentary of 2 cm long, 2--4 mm wide and 0.5--1 cm high ( Figure 5B View FIGURE 5 ). The anterior part is broken ventrally. In occlusal view, 14 teeth emplacements are visible with the crown base. All the teeth show folds ( Figure 5C View FIGURE 5 ). Teeth are circular in cross-section, 2 mm wide. However, only the base is preserved, preventing them from further description. The second jaw fragment is too damaged to identify what bone it is accurately. The circular structures with a similar pattern representing the dentary might suggest it was a tooth-bearing bone of a temnospondyl; however, we cannot determine whether it is a maxillary or a dentary.

Teeth ( Figure 5 View FIGURE 5 D-G): The 20 isolated teeth are conical and display longitudinal grooves on the lower portion of the crown surface. These teeth are conical, massive, weakly lingually curved, and asymmetrical. The labial surface is more convex in lateral view and rounded in cross-section than the lingual surface. On both mesial and distal sides, the carina exhibits sharp edges. The folds run from the base to the middle of the crown surface but never to the upper part. They vary significantly; the largest tooth has a crown height of 1.7 cm long and a crown base of 75 mm long and 0.6 mm wide; the smallest has a crown height of 3 mm long and a crown base of 2 mm long and 1.5 mm wide.

Remarks. The longitudinal grooves on the isolated teeth and the folds in the teeth of the jaw are typical of temnospondyls, known to possess laby-

rinthodont teeth. The infolding of their enamel and dentine results in longitudinal grooves on the lower part of the teeth (Kowalski et al., 2009; Rinehart and Lucas, 2013). Many temnospondyls have been found in the Late Triassic of Jameson Land, such as Aquiloniferus kochi , Selenocara groenlandica ,

Stoschiosaurus nielseni, Tupilakosaurus heilmani,

Cyclotosaurus naraserluki , and Gerrothorax (Marzola et al., 2018) , which has already been mentioned earlier. The material is only referred to as Temnospondyli indet. since it does not have any characters, allowing a deeper identification.