DOSWELLIIDAE Weems, 1980

Clade DOSWELLIIDAE Weems, 1980 Doswelliidae indet.

( Figure 6 View FIGURE 6 D-E)

Specimens referred. NHMD–1811719 – osteoderm.

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. Missing its edges, the osteoderm is sub-rectangular. Its dorsal surface is ornamented by a prominent keel running all along the plate and more than 20 central regular pits of subequal size and contour on two-thirds of the total length of the osteoderm ( Figure 6D View FIGURE 6 ). The remaining third, the anterior articular lamina, is a smooth surface devoid of pits with a less prominent keel, thinner than the rest of the plate. The internal surface is convex and crossed by longitudinal striations bifurcating to the centre, corresponding to the position of the keel ( Figure 6E View FIGURE 6 ).

Remarks. Since phytosaurs are known with the recently described M. alleroq , it might seem logical to attribute this osteoderm to that species. López-Rojas et al. (2022) described four morphotypes of osteoderms in their supplementary data. We immediately refute the fourth morphotype hypothesis due to the obvious different ornamentation between them and NHMD–1811719, as it consists of small, interconnected ridges in the fourth morphotype. The second morphotype is characterised by a dorsal keel near the medial edge, while it is present in the middle of the dorsal surface in NHMD–1811719. Both the first and third morphotypes display a central mid-dorsal keel, however, the first morphotype keel is more sub-circular and not as prominent and marked as in NHMD– 1811719. Regarding the third morphotype, it displays strong lateral projections giving a triangular shape to the osteoderm, which are not present in NHMD–1811719. Moreover, pits in osteoderms of M. alleroq are irregular in size contrary to the regular ones in NHMD–1811719.

Another group of vertebrates wearing osteoderm in the Triassic of Greenland is Aetosauria, represented by Aetosaurus ferratus Fraas, 1877 and Paratypothorax andressorum Long and Ballew, 1985 (Jenkins et al., 1994), both specimens preserved with some osteoderms. Osteoderms of A. ferratus are ornamented with “radiating, oblong, closely, appressed grooves on smooth-surfaced plates”, while in P. andressi they display “an eccentrically placed eminence and radiating groves” (see Jenkins et al., 1994). The difference in ornamentation between Aetosauria and NHMD–1811719 immediately refutes the attribution of the latter to the said group.

Another possibility could be Aetosauriformes such as Revueltosaurus callenderi Hunt and Lucas, 1989 with dorsal paramedian osteoderms (PEFO 34561 and PEFO 42442) described by Parker et al, (2021) as “ornamented with a random pattern or incised circular and oblong pits and having a distinct raised anterior bar along the anterodorsal edge”. NHMD–1811719 differs by the regularity of its pits and the presence of a more prominent dorsal keel. In R. callenderi , there are also caudal osteoderms (PEFO 34561) which are remarkable for a sharp, raised keel, much more than in NHMD–1811719, but a weak pits ornamentation (Parker et al., 2021), contrary to NHMD– 1811719 which has at least two rows of pits on both side of its keel.

The specimen is comparable to the osteoderm of Doswelliidae , a group of non-Archosauria archosauriform known from the Middle Triassic to Upper Triassic in North America, Germany, Poland, and South America (Sues et al., 2013; Czepiński et al., 2023). The clade has two unambiguous synapomorphies among non-Archosauria archosauriform on the osteoderm established by Desojo et al. (2011): (1) ornamentation coarse, incised, and composed of central regular pits of equal size and (2) the presence of an unornamented anterior articular lamina. The description seen before does match these two synapomorphies. The clade is represented in the Norian by one species, Doswellia kaltenbachi Weems, 1980 from the Chinle Formation ( USA) (Parker and Barton, 2008; Parker et al., 2021). It is the closest to our specimen, both in space and time. The only species known in Europe is Jaxtasuchus salomoni Schoch and Sues, 2014 , from the Ladinian of Erfurt Formation, Germany (Schoch and Sues, 2014) and in the Lower Keuper of Poland (Czepiński et al., 2023). The difference that can be noted between Jaxtasuchus and our material is that the dorsal keel of NHMD–1811719 seems to develop anteriorly, covering the lamina, while in Jaxtasuchus , the anterior articular lamina is flat and smooth. Despite this, and due to the small amount of material available, only one osteoderm, we keep the identification as Doswelliidae indet. since more material is required to go further in the identification.

Superorder LEPIDOSAURIA Haeckel, 1866

Order RHYNCHOCEPHALIA Günther, 1866

Suborder SPHENODONTIA Williston, 1925

Family CLEVOSAURIDAE Bonaparte and Sues, 2006 Clevosauridae indet.

( Figure 6 View FIGURE 6 F-K)

Specimens referred. NHMD–1811692 – left maxilla; NHMD–1811693 – right maxilla.

Locality. From site 62/91/G and 64/91/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. The first specimen, NHMD–1811692, is a section from the left maxilla, measuring 3.95 mm long, 0.85 mm wide, and 1.3 mm high without the teeth ( Figure 6 View FIGURE 6 F-H). Its anterior and posterior margins are both missing. During previous preparation, the specimen was fixed on a nail by a glue bubble, preventing any description of the dorsal margin. To avoid damaging it, it is kept as is. In the lateral view, the maxilla is partially covered by sediments, ( Figure 6F View FIGURE 6 ). The medial surface is smooth and displays a thick layer that forms a ledge at the bases of the teeth ( Figure 6 View FIGURE 6 G-H). The ledge is 0.48 mm long labio-lingually. It bears five acrodont teeth, circular in cross-section and with rounded tips, attached to a smooth and thin secondary bone. Their base is elongated anteroposteriorly due to posteromedial flanges, visible in lateral and occlusal views ( Figure 6 View FIGURE 6 G-H). Except for the rounded apex resulting from use, the lack of important wear patterns on the specimen indicate it must be a juvenile or a sub-adult individual. The average dimensions of the teeth are 0.47 mm long mesio-distally and 0.37 mm wide labiolingually at the crown base and 0.52 mm high for the crown height.

NHMD–1811693 is a tooth-bearing bone, a right maxilla. It measures 2.25 mm long, 1 mm wide and 1.5 mm high ( Figure 6 View FIGURE 6 I-K). The shape of the anterior extremity suggests that it is the most anterior part of the bone, showing the first four maxillary teeth ( Figure 6I, K View FIGURE 6 ). Its dorsal margin is broken, as is the posterior part. The lingual and labial edges deviate from each other as they approach the dorsal margin (which is absent). In the dorsal view, the internal structure of the bone is visible, characterised by spongiosis. The dorsal part is concave. Four acrodont conical additional teeth are present on the bone. They are circular in cross-section, slightly extended anteroposteriorly, with sharp triangular posteromedial flanges ( Figure 6 View FIGURE 6 I-J). They are sharper and higher than the previous specimen but still rounded at the tip. Similarly, they have no sign of wear pattern, suggesting it is a sub-adult considering the additional teeth. The teeth measure, on average, 0.5 mm long and 0.25 mm wide at the base, and 0.5 mm high.

Remarks. The two specimens were previously identified and mentioned as Sphenodontia indet. by Jenkins et al. (1994). NHMD–1811692 was found in association with two premolariform teeth of Kuehneotherium sp. (Jenkins et al., 1994) of the Carlsberg Fjord Member, while NHMD–1811693 was with eight teeth of the same species in a dolomitic limestone at the top of Tait Bjerg, corresponding to the Tait Bjerg Member (Jenkins et al., 1994). Both specimens are considered as maxilla fragments, NHMD–1811692 being the middle part as the three most anterior teeth are hatchling teeth while the two last are additional ones, and NHMD– 1811693 would be the part that articulate with the jugal, indicated by the concave dorsal surface (see Chambi-Trowell et al., 2021). Both specimens show multiple features that are typical of sphenodontians. First, the presence of an acrodont dentition is a typical trait of the group (Hsiou et al., 2019; Chambi-Trowell et al., 2021). Then, the secondary bone at the base of the marginal dentition of NHMD–1811692 is characteristic of sphenodontians (Williston, 1925; Hsiou et al., 2019). However, the secondary layer of the first specimen is very thick compared to other specimens. Still, a similar condition seems to be present in a juvenile specimen (UFRGS-PV-0613-T) of Microsphenodon bonapartei Chambi-Trowell et al., 2021 , from the Late Triassic of Brazil (Romo-de-Vivar-Martínez et al., 2021: figure 4b-c, p. 5). NHMD–1811693 does not have a secondary bone, making it difficult to identify it accurately. The alternation in size of the hatchling teeth is also characteristic of sphenodontians (Harrison, 1901; Fraser, 1988). The posteromedial flanges are present in many sphenodontians, particularly the species of Clevosaurus Swinton, 1939 (Sues et al., 1994; Säilä, 2005; Jones, 2006a; Romo-de-Vivar-Martínez and Bento Soares, 2015; Hsiou et al., 2015, 2019; O’Brien et al., 2018). The shape of the teeth and the sharp posteromedial flanges are according to the omnivorous or carnivorous diet of clevosaurs (Jones, 2006b; Rauhut et al., 2012; Martínez et al., 2013). NHMD–1811692 and NHMD–1811693 are similar to juvenile Clevosaurus maxillae from the Triassic of Britain and Brazil, displaying the same type of dentition (Fraser, 1988, figure 40; Romo-de-Vivar-Martínez and Bento Soares, 2015, figure 4f-g; Romo-de-Vivar-Martínez et al., 2021, figure 4b-c). Based on these similarities with clevosaurs, we tentatively assign these two specimens to Clevosauridae .