TRICONODONTA, Osborn, 1888

Prasad, Guntupalli V. R. & Manhas, Brijesh K., 2002, Triconodont mammals from the Jurassic Kota Formation of India, Geodiversitas 24 (2), pp. 445-464 : 452-453

TRICONODONTA indet. ( Figs 2F, G ; 3F, G )

REFERRED MATERIAL. — VPL/JU/KM/15, fragmentary lower left molar.

HORIZON AND LOCALITY. — Mudstones associated with the limestone bands of Kota Formation, west of Paikasigudem village, Rebbana Mandalam, Adilabad District, Andhra Pradesh (State), India.

DESCRIPTION

The specimen is a partial lower molar (length of preserved specimen = 0.814 mm, maximum preserved width = 0.465 mm). The anterior cusps and anterior root are broken off. The main cusp a is half preserved. It is the highest and largest cusp with a flat lingual face. It is connected to the small posterior cusp c (less than half the height of cusp a) by a posterior crest. The main cusp is vertical in the orientation of its long axis, whereas cusp c is slightly reclining posteriorly making an acute angle with that of cusp a ( Figs 2G ; 3F ). It is separated from cusp a by a shallow V-shaped notch. The lingual face of cusp c is also flat. The posterior accessory cusp d is a very small, cingular cusp and is prolonged anterolingually by the lingual cingulum, which possibly bears two incipient cingular cuspules. Anterior to these cuspules, the cingulum becomes reduced and indistinct at the level of the middle of cusp a. The labial face of a is acutely angulated. A slight basal swelling is present between the cusps a and d. The labial face of cusp c is also convex, but less than that of cusp a. The posterior face of the crown is rounded. The enamel of the crown is poorly preserved. Hence it is difficult to say whether wear facets were present or not, though there appears to be a wear facet on the posterolabial face of a and an indistinct one on the labial face of cusps c and d ( Fig. 3G ). The labial tip of cusp c is also worn ( Fig. 3G ). The posterior root is anteroposteriorly long at the base of the cusps and supports the entire preserved part of the crown. This root tapers ventrally and is moderately flattened labiolingually. It has convex anterior and posterior faces. A very shallow sulcus extends from the base of the crown (below the junction of cusps a and c) to mid-length of the root.

COMPARISONS

Incompleteness of the tooth does not allow any definitive comments on its taxonomic position. Nevertheless, the presence of a high principal cusp with its long axis vertically oriented and an accessory cusp c with its long axis diverging away from that of a is seen in some amphilestines and gobiconodontines as well as Jeholodens . The latter and Tendagurodon differ from VPL/JU/KM/ 14 in the absence of a distinct lingual cingulum. If the wear facets observed for VPL/JU/KM/14 are correct, then the occlusion pattern for this tooth can be supposed to be similar to that of Morganucodon .

Figures

FIG. 2. — A-E, left lower molar, holotype (VPL/JU/KM/13); A, lingual view; B, labial view; C, occlusal view; D, posterior view; E, ante- rior view; F, G, Triconodonta indet., fragmentary left lower molar (VPL/JU/KM/15); F, labial view; G, lingual view. Scale bar: 0.5 mm.

FIG. 3. — A-E, Dyskritodon indicus n. sp., left lower molar, holotype (VPL/JU/KM/13); A, lingual view; B, labial view; C, posterior view; D, anterior view; E, occlusal view; F, G, Triconodonta indet., fragmentary left lower molar (VPL/JU/KM/15); F, lingual view; G, labial view. Abbreviations: a-f, cusps a-f; licc, lingual cingular cuspule;?w. f.,?wear facet. Hatched areas represent wear facets and crossed hatching demarcates broken areas in all figures. Scale bar: 0.5 mm.