Lissodus sp.
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publication ID |
https://doi.org/ 10.5281/zenodo.13514789 |
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persistent identifier |
https://treatment.plazi.org/id/03DF87A9-A309-FF96-4106-FBADB3B5FA0F |
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treatment provided by |
Felipe |
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scientific name |
Lissodus sp. |
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Lissodus sp. Morphotype 5
Fig. 6 View Fig .
Diagnosis.—Isolated microscopic hybodontoid teeth. Enameloid crown; labio−lingually compressed with four to eight non−differentiated cusps, asymmetric, blade like. Narrow median crest extends from lateral edge to lateral edge lying more to the dorso−lingual; main cusp off centre, higher than the lateral cusps with a subdued vertical ridge descending from the apex lingually, labially ridge bifurcates before the crown−base interface (may bifurcate a second time) delineating a labial buttress; lateral non−differentiated cusps are outlined in most instances by shallow grooves on both aspects, though some evidence of ridging may also occur. Base outline elongate, ventrally slightly concave with furrows radiating towards the centre; lingually base is long and sloping with at least seven deep furrows and foramina, labially short, punctuated by foramen.
Material.—Five figured, isolated specimens, TCD.36775, 76, TCD.36778, TCD.36783, 84. Seven other isolated specimens (some incomplete), TCD.36777, TCD.36779, 80, TCD.36785–88.
Description.—The length along the median crest ranges from 0.7 mm to 1.33 mm (in most cases the length of the base is very slightly less than or equal to that of the crown); labio−lingually the width of the crown ranges from 0.12 mm to 0.24 mm (base, 0.22 mm to 0.39 mm); the lingual height ranges from 0.24 mm to 0.46 mm (crown, 0.1 mm to 0.32 mm). The median crest is very narrow along the narrow blade−like crown. Cusps on both aspects are differentiated only by shallow oblique grooves from this crest towards the crown−base interface. Hence in lateral view the crown is lenticular in outline. Very subdued ridging occurs in some specimens. Lingually the crown−base interface is arcuate. The main cusp is higher than the lateral cusps and forms a labial buttress (lateral compressed) outlined in most instances by a vertical descending ridge that bifurcates at least once; subdued ridges may occur on the remaining labial cusps in some specimens. The lingual base is long, sloping and slightly convex; embayments may be seen at both lateral edges, though the crown is usually less than or equal to the length of the base. Up to seven deep furrows ending in foramina incise the lingual base from the linguo−ventral margin towards the arcuate crown−base interface. Labially, the base is one−third to one−quarter the length of the lingual surface, with a slightly convex labio−ventral margin, a few expanded pits occur; the ventral surface is concave especially along the labio−ventral margin from which a number of short furrows run in toward the central area while the linguo−ventral area is flatter.
Discussion.—Morphotypes 1 and 5 are similar in the blade−like nature of their crowns, the presence in some specimens of small labial nodes at the crown−base interface and common occurrence of a minor lingual buttress. However, Morphotype 5 tends to be smooth crowned, i.e. without vertical ridges, which contrasts with the strongly ridged Morphotype 1.
Age, locality, and lithology.—Kilbride Limestone Formation, Polygnathus mehli conodont Biozone, Ivorian (probably Freyrian), late Tournaisian, Dinantian. Disused quarry, near Nobber, Co. Meath (N 845 848); crinoidal limestone.
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