Lissodus lepagei Duffin, 1993a

Lissodus lepagei Duffin, 1993a

( Figure 2 View FIGURE 2 A-H)

Specimens referred. NHMD–1811650 – tooth; NHMD–1811651 – tooth; NHMD–1811652 – tooth; and 270 additional teeth were identified and stored under collections number NHMD–1811705.

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).

Emended diagnosis. Teeth of Lissodus , which range from very small (around 0.5 mm) to moderately small (up to 3 mm), showing moderate heterodonty. Coronal morphology is generally conservative with a low to high principal cusp, in posterior and anterior teeth, respectively, up to three pairs of lateral cusplets and a crenulate occlusal crest. The moderate to strong labial peg (around 0.5 mm) possesses a strong accessory cusplet and shows considerable variation in shape in occlusal view. Fine to strong vertical ridges are confined to upper lingual and upper labial faces of the crown. A horizontal ridge surrounds the crown at the top of the crown shoulder, without anastomosis.

Description. From the collection, 273 teeth have been assigned to Lissodus lepagei . Those teeth strongly vary in size, from less than 1 mm to almost 3 mm long mesiodistally, never exceedingly further. The crown profile is gracile and narrow, although it can be thicker. The height and width of the crown vary on the tooth, but it is usually 0.5 mm high, excluding the cusps, and 0.4 mm wide labiolingually. The tooth is weakly curved lingually. The crown possesses a high principal cusp and up to three pairs of lateral cusplets in some teeth. The horizontal ridge circles all around the crown at the crown shoulder, at the middle height of the crown.

The occlusal crest, being particularly salient, is positioned at the mesiodistal length of the crown,

extending through the apices of the principal cusp and lateral cusplets. Each cusp/cusplet is ornamented by at least one vertical ridge on both lingual and labial faces descending from the apices to the horizontal ridge. The principal cusp may display two other non-branching vertical ridges on both sides. Otherwise, the crown surface is smooth. The labial peg is moderately strong and rounded, surmounted by an additional cusplet, discernible depending on the tooth, while the lingual peg is less prominent ( Figure 2 View FIGURE 2 A-B). The root is preserved on a dozen specimens. It is as high as the crown, approximately 0.5 mm. The crown/root junction is deeply incised around the tooth. It is lingually directed, with its lingual and labial sides showing aligned foramina. Two morphotypes have been identified ( Figure 2 View FIGURE 2 A-B, E-H), though there is a continuous spectrum of shape variation, with teeth showing an intermediate state of characters suggesting a position between the two morphotypes ( Figure 2 View FIGURE 2 C-D), representing only the extreme of this spectrum.

Morphotype “ Lissodus lepagei 1” (LL1) ( Figure 2 View FIGURE 2 AB): It is usually the longest mesiodistally morphotype present. It has the highest cusp, with a height of 1 mm from the crown and lateral cusplets. Concerning the latter, they are longer than high; their height is never higher than half of the principal cusp. The labial peg is prominent and distinguishes itself from the rest of the tooth. The accessory cusplet ornamenting the labial peg is present, although, due to erosion, it can be difficult to discern it or even absent in strongly eroded specimens.

Morphotype “ Lissodus lepagei 2” (LL2) ( Figure 2 View FIGURE 2 EH): This morphotype is stockier with a lower principal cusp. The lateral cusplets may be absent or less distinguishable. The base is usually concave. In some specimens, the labial vertical ridge descending from the apex of the principal cusp may end at the labial peg ornamented by an accessory cusplet, usually more prominent than in Morphotype LL1.

Remarks. The assignment to Lissodus is based on the presence of a labial protuberance gently slop-

ing towards the crown base (the labial peg), a triangular crown shape in occlusal view, a root lingually inclined marked by a row of small circular foramina on both lingual and labial side (Rees and Underwood, 2002). The description of the numerous specimens from Jameson Land Basin matches the diagnosis of Lissodus lepagei from the middle Norian of Luxembourg, as described by Duffin (1993a). Both specimens from Greenland and Luxembourg have a crenulated occlusal crest, with up to three pairs of lateral cusplets and a variableshaped labial peg surmounted by a cusplet in some cases (Duffin, 1993a). This species, unlike other Lissodus species, is barely known in the fossil record, reported only in middle Norian of Western Europe countries like France (Grozon), Luxembourg (Syren and Medernach), and probably the Middle Triassic of Spain (Duffin, 1993a; Cuny et al., 1998; Godefroit et al., 1998; Pla et al., 2013). The labial peg is moderately to strongly prominent, sometimes angled mesiodistally. As in the Medernach specimens, the accessory cusplet is present in most of the teeth, but it can be absent due to erosion. Contrary to the specimens from Medernach (Duffin, 1993a), there is a higher degree of variation in size, and morphologically, it could be interpreted as a monognatic heterodonty where Morphotype LL1 might be anterior or lateral teeth, and Morphotype LL2 represents posterior teeth. Morphotype LL2 shows strong morphological similarities with the specimens from Medernach (e.g., holotype BM(NH) P. 62633 in Duffin, 1993a), with a similar size ( 1 mm long mesiodistally), an occlusal crest with a cutting edge surmounted by a low principal cusp and up to three pairs of lateral cusplets, ornamented by vertical ridges restricted to the upper part of the crown, and a prominent labial peg with an accessory cusplet. Morphotype LL1 differs only by having a very high principal cusp, demarcating itself from the rest of the crown. Following these differences (higher degree of heterodonty, anterior teeth with more prominent principal cusp and a greater range of size variation), we emended the diagnosis as seen previously in the text.

We exclude the identification as to Lissodus nodosus (Seilacher, 1943) , known from the Norian of Germany (Duffin, 2001), by the presence of labial and lingual nodes, the lack of prominent lateral cusplets and horizontal ridge on the crown and a labial peg devoid of any accessory cusplet as described in the holotype SMNS 50.214. For similar reasons, the possibility of Lissodus angulatus (Stensiö, 1921) or Lissodus africanus (Broom, 1909) is ruled out as both differ from our specimens by the absence of the accessory cusplet on the labial peg, the lack of lateral cusplets, and no horizontal ridge around the crown shoulder. Moreover, L. lepagei has more gracile teeth with entirely distinguishable cusps, as opposed to the wide labiolingually and low crown present in most Lissodus species (Duffin, 2001). For this study, L. lepagei is considered a valid species of Lissodus , but we recognise that more work on the systematics of Hybodontiformes is needed. For example, L. lepagei was thought to represent juvenile specimens of Lissodus minimus ; however, due to the absence of adult L. minimus from the material of Medernach ( Luxembourg) this hypothesis might be refuted (Duffin, 1993a). Interestingly, Morphotype LL1 teeth also share similarities with teeth of Parvodus rugianus (Ansorge, 1990) , an Early Cretaceous species displaying moderately high principal cusp, two to three pairs of lateral cusplets and a labial peg rounded (Rees, 2002). Parvodus dentition is characterised by a low degree of monognatic heterodonty (Rees, 2002, Rees et al., 2013). The original author, Ansorge, assigned his specimens to Lissodus before they were reviewed as Parvodus (Rees and Underwood, 2002) .