Lissodus, Brough. Neues Jahrbuch, 1935

Lissodus cf. Lissodus minimus (Agassiz, 1836)

( Figure 2 View FIGURE 2 I-N)

Specimens referred. NHMD–1811662 – tooth; NHMD–1811663 – tooth; NHMD–1811664 – tooth; and 174 additional teeth were identified and stored under collections number NHMD–1811707.

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. Among the 177 teeth of Lissodus cf. Lissodus minimus , the size varies between morphotypes but never exceeds 3 mm long, except for one incomplete specimen measuring 3.5 mm mesiodistally, with one cusp end missing. The height and width of the crown vary but are around 0.3 mm and 0.5 mm, respectively. The tooth is often curved lingually and has a concave base. The crown comprises a diamond-shaped principal cusp. One pair of low lateral cusplets may be present in some teeth. Different types of ridges ornament the surface of the crown. The horizontal ridge is at the level of the crown shoulder and runs all around the tooth. The occlusal crest runs along the mesiodistal length, passing through the apices of the principal cusp and lateral cusplets. Vertical ridges descend from the apices of the principal cusp and the occlusal crest and lateral cusplets when present. The labial side exhibits a low labial peg perpendicular to the occlusal crest, pointing toward the base of the crown. It can be prominent according to the morphotype. The lingual peg may be less discernible ( Figure 2N View FIGURE 2 ). The distal ends of the crown are rounded. When preserved, the root is less deep than the crown. The crown/root junction is deeply incised around the tooth. The root follows the same concavity as the base. It is as high as the crown, approximately 0.5 mm. It is lingually directed and ridged horizontally on the labial side,

with vascular foramina running parallel to the crown base. Variations have been observed between the numerous specimens, some with eroded cusps and crown surfaces, removing the ridges. At least three morphotypes have been observed in the collection.

Morphotype “ Lissodus minimus 1” (Lm1) ( Figure 2 View FIGURE 2 I-J): It is usually the smallest morphotype, up to 1.5 mm long. Unlike the pyramidal principal cusp, the crown is lower distally and weakly ridged, almost smooth. Lateral cusplets can be present, their top being lingually curved. The peg is triangular in occlusal view.

Morphotype “ Lissodus minimus 2” (Lm2) ( Figure 2 View FIGURE 2 K-M): It is an intermediate morphology between Morphotype Lm1 and Morphotype Lm3 (see below). They are 2 mm long and 0.5-- 1 mm wide. They are slightly curved lingually and concave at the base. The teeth show a low crown; the horizontal ridge is closer to the base. The principal cusp is pyramidal and very wide, more bulbous than in the previous morphotype Lm1, while the mesiodistal ends are thinner (half the width of the principal cusp). Lateral cusplets are absent in this morphotype. The labial peg is lower and rounded, shaped like a ‘U.’ The surface is strongly vertically ridged, but the occlusal crest is less sharp than on the anterior teeth.

Morphotype “ Lissodus minimus 3” (Lm3) ( Figure 2N View FIGURE 2 ): This morphotype regroups the most robust teeth. The crown is longer mesiodistally and wider labiolingually. The principal cusp is domed-shaped and lower. The peg cannot be distinguished from the cusp. The base is curved but far less than in the other morphotypes. The tooth is also curved lingually at the distal part. The horizontal ridge is difficult to distinguish as the crown profile is very low. This is the morphotype with most vertical ridges descending from the apex, showing bifurcation between them. No root has been preserved.

Remarks. As for L. lepagei , the assignation to Lissodus is based on a labial peg, a triangular crown shape in occlusal view and a lingually inclined root ornamented by foramina on both the lingual and labial sides (Rees and Underwood, 2002). It is helped by the overall morphology similar to Lissodus minimus (Agassiz, 1836) : domed teeth with low cusp, broad and triangular labial peg, and ornamentation with numerous ridges (Duffin, 1985). This species is well known in Northwestern and central Europe: Britain (Allard et al., 2015; Moreau et al., 2021), France (Duffin, 1993b [Saint- Nicolas-de-Port]; Cuny et al., 2000 [Lons-le-Saunier]), Belgium (Duffin and Delsate, 1993), Luxembourg (Syren and Medernach) (Godefroit et al., 1998), Germany (Konietzko-Meier et al., 2019), and Poland (Duffin and Gaździcki, 1977) (Fischer, 2008). Recently, it has been observed in the English Rhaetian on numerous occasions (Korneisel et al., 2015; Norden et al., 2015; Slater et al., 2016; Cross et al., 2018; Moreau et al., 2021), allowing comparison of recently discovered specimens showing multiple examples of the monognathic heterodonty, with three to five different morphotypes: anterior, anterolateral, lateral, postero-lateral, and posterior. Lm1 could be an anterolateral tooth morphotype of Lissodus cf. L. minimus, Lm 2 a lateral tooth, and Lm3 a posterior tooth. Duffin (1985) observed two main tooth types that are matched by morphotypes Lm1 and Lm2 (e.g., BGM CD 55 and BGM CD 56 for the first type), and Lm3 (e.g., BGM CD 57 and BGM CD 58 for the second type). According to the author, BGM CD 55 is a mesial tooth, BGM CD 56 an anterolateral tooth, BGM CD 57 a lateral tooth, and BGM CD 58 an extreme lateral tooth (Duffin, 1985), corresponding to the attributed position of Greenland morphotypes. Also, most of the changes mentioned by Duffin (1985) are observed between morphotypes, taking place distally through the dentition starting from the anterior teeth like elongation mesiodistally, the crown becoming shallower, an increase of vertical ridges number and their bifurcation. Since lateral cusplets are absent in most teeth, and their dimensions do not match those of L. minimus described by Duffin (1985, 1993b, 2001), we prefer to use L. cf. L. minimus to refer to the specimens from Greenland.

Hybodontiformes indet.

( Figure 2 View FIGURE 2 O-S)

Specimens referred. NHMD–1811665 – dorsal spine; NHMD–1811666 – dermal denticle; NHMD– 1811667 – cephalic spine; NHMD–1811726 – dorsal spine; NHMD–1811727 – dorsal spine; NHMD– 1811728 – dorsal spine; NHMD–1811729 – dorsal spine; NHMD–1811730 – dorsal spine; NHMD–

1811731 – dorsal spine; NHMD–1811732 – dermal denticle; NHMD–1811733 – dermal denticle;

NHMD–1811734 – dermal denticle; NHMD–

1811735 – dermal denticle; NHMD–1811736 – dermal denticle; NHMD–1811737 – dermal denticle;

NHMD–1811738 – cephalic spine; NHMD–

1811739 – cephalic spine; NHMD–1811740 –

cephalic spine; NHMD–1811741 – cephalic spine;

NHMD–1811742 – cephalic spine; NHMD–

1811743 – cephalic spine; NHMD–1811744 –

cephalic spine; NHMD–1811745 – cephalic spine;

NHMD–1811746 – cephalic spine; NHMD–

1811747 – cephalic spine; NHMD–1811748 –

cephalic spine; NHMD–1811749 – cephalic spine;

NHMD–1811750 – cephalic spine; NHMD–

1811751 – cephalic spine.

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. Seven dorsal spines, about 15

cephalic spines and seven dermal denticles of

Hybodontiformes have been identified, although more precise identification was impossible.

Dorsal spines ( Figure 2O View FIGURE 2 ): The largest dorsal spine is 1.7 cm long and 6 mm wide. They have very pronounced horizontal ridges on the lateral sides and cusplets along the posterior margin. They tend to curve posteriorly in their distal parts.

Cephalic spines ( Figure 2 View FIGURE 2 P-Q): The cephalic spines have two parts: a base and a crown. The crown is not preserved on any specimen presented here. Most specimens are the T-shaped, tri-radiate base comprising three equally wide branches. The branches are rounded at the end and slightly bent. The surface is usually porous. When the specimen is complete, the crown is the enamelled fourth and most extended branch (compare with Leuzinger et al., 2017: figure 4A- D, p. 476).

Dermal denticles ( Figure 2 View FIGURE 2 R-S): The dermal denticles have a circular base and a crown. The crown is a cone-like structure with vertical ridges originating at the apex, extending basally to the cusp neck (compare with Klug et al., 2010: figure 5, p.252). The ridges can be more or less pronounced.