Theropoda

Meso, Jorge G., Hendrickx, Christophe, Baiano, Mattia A., Canale, Juan I., Salgado, Leonardo & Díaz-Martínez, Ignacio, 2021, Isolated theropod teeth associated with a sauropod skeleton from the Late Cretaceous Allen Formation of Río Negro, Patagonia, Argentina, Acta Palaeontologica Polonica 66 (2), pp. 409-423 : 412-415

publication ID	https://doi.org/ 10.4202/app.00847.2020
persistent identifier	https://treatment.plazi.org/id/B91FFD0B-B769-9E79-FCE0-F823FEF7F97A
treatment provided by	Felipe
scientific name	Theropoda
status

Treatment

Theropoda Marsh, 1881

Ceratosauria Marsh, 1884

Abelisauroidea Bonaparte, 1991

Abelisauridae Bonaparte and Novas, 1985

Gen. and sp. indet.

Figs. 2–4 View Fig View Fig View Fig .

Material.—The isolated teeth IIPG-01 to IIPG-12 from “Dino 1” site (S 39°08’; W 67°40’), Paso Córdoba locality, 14 km southwest of the town of General Roca, Río Negro Province; Allen Formation (middle Campanian–early Maastrichtian, Upper Cretaceous; Garrido 2011; Paz et al. 2014).

Description.—The isolated teeth, which are almost complete, are interpreted as shed crowns due to the absence of most of the root. The IIPG-02, -05, -06, -08, and -09 show the basal portion of the root and are the best-preserved of the sample. The apical two-thirds of the crown apex has been worn out along its mesial margin in IIPG-01, whereas a basal portion of the crown on the lingual surface, and ~ 2 mm of the apical portion of the distal carina are missing in IIPG-04. The IIPG-03, -07, -10, -11, and -12 are the most damaged teeth. They lack the basal portions of the crowns on both the labial and lingual surfaces. In addition, the distal carina is missing along the basal two-thirds of the crown, while denticles on the mesial carina are worn out and poorly preserved. IIPG-07 lacks its apical portion, whereas IIPG-10 lacks its apico-distal portion, the basal portion, and the two-thirds basal mesial margin. Respect to IIPG-11, it only consists of an apical portion of the crown, while IIPG-12 lacks its basalmost portion of the crown.

Morphotype I: IIPG-02 ( Fig. 2 View Fig ) and IIPG-03. Crowns of Morphotype I are characterized by a weak labiolingual compression at the crown base (CBR> 0.7; Table 1), and by being moderately apicobasally elongated (2 <CHR ≤ 2.5). The mesial margin is strongly apicobasally and labiolingually convex. The distal margin of the crown IIPG-03 is straight to slightly concave in lateral view, with the apex almost at the same level of the distal carina. In IIPG-02, the distal margin is apico-basally convex, with the apex positioned almost on the middle of the crown ( Fig. 2 View Fig ). Both labial and lingual surfaces are mesiodistally convex, and the lingual surface is strongly apicobasally concave ( Fig. 2 View Fig ). The two crowns show well-developed mesial and distal carinae. In mesial view, the carina is straight and centrally positioned on the crown. However, the basalmost portion of the mesial carina is missing, so that it is unknown whether the denticles extended to the cervix or just above it. In distal view, the carina extends to the cervix and is either centrally positioned on the crown or slightly displaced labially. Teeth of Morphotype I have a salinon-shape (i.e., with labial margin convex and lingual margin biconcave) cross-sectional outline at the base crown ( Fig. 2 View Fig ). Two concave surfaces adjacent to the mesial and distal carinae are seen and restricted to the lingual surface of the crown.

In IIPG-02, the mesial carina bears 10–11 denticles per 5 mm close to the apex, 10–12 denticles per 5 mm at mid-crown, and 12–16 denticles per 5 mm at the crown base. The distal denticle density ranges between 10–11 close to the apex, 10 at mid-crown, and 14 at the crown base. If the number of denticles is unknown at the base and mid-crown due to damage, IIPG-03 shows the same denticle density as IIPG-02. The denticle density increases gradually apically along both carinae. With a DSDI ranging from 1–1.2, there is no discrepancy between mesial and distal denticles. The latter are chisel-shaped, apically inclined, sub-quadrangular at the base, and their external margin is symmetrically convex. The denticles are also longer mesiodistally than baso-apically along all the carina. The mesiodistal main axis of the denticles is arranged at an acute angle to mesial and distal margins. IIPG-03 shows narrow interdenticular space and there are no interdenticular sulci between the denticles. Conversely, the interdenticular sulci are clearly visible in IIPG-02 where they are particularly well-developed at mid-crown.

The labial surface of IIPG-02 shows pronounced marginal undulations adjacent to the distal carina and covering the apical two-thirds of the crown surface. Teeth from Morphotype I, however, appear to lack transverse undulations, flutes, longitudinal grooves (which should not be confused with the concave surfaces adjacent to the carinae), and ridges. The texture is irregular and not oriented in any preferential direction in these two crowns.

Morphotype II : IIPG-07, -08, and -09 ( Fig. 3 View Fig ). Similar to Morphotype I, the crowns possess a typical ziphodont morphology, with a distal curvature, important labiolingual compression of the crown (CBR ≥ 0.5; Table 1), and a weak apicobasal elongation (CHR ≤ 2). The mesial margin is strongly convex both apico-basally and labiolingually in lateral and basal views, respectively. The distal margin is straight so that the apex is located at the level of the distal carina ( Fig. 3 View Fig ). Both labial and lingual surfaces are strongly mesiodistally convex, as seen in Morphotype I. The crown bears well-developed mesial and distal carinae. In IIPG-08, the mesial carina is almost straight and slightly lingually deflected; conversely, the mesial carina is strongly lingually deflected in IIPG-09 ( Fig. 3 View Fig ). The denticles extend to the cervix in IIPG-09. It is, however, unknown whether the mesial carina extends to the root or just above it in IIPG-08. The distal carina is strongly displaced labially in IIPG-09, whereas it is centrally positioned to slightly displaced in IIPG-08. In each crown, the distal denticles all extend to the root or directly beneath the cervical line. A depression adjacent to the distal carina can be seen along the labial surface of the crown. The cross-section is lanceolate with acute and well-developed distal carina ( Fig. 3 View Fig ).

As for Morphotype I, the mesial and distal carina show a gradual increase of the number of denticles per 5 mm towards the crown base. We counted 11–13 mesial denticles per 5 mm close to the apex, 13–15 at mid-crown, and 13–16 mesial denticles at the crown base. The distal carina shows a denticle density of 13–16 denticles per 5 mm close to the apex, 14 denticles at mid-crown, and 15–16 denticles at the crown base. The mesial denticles are therefore slightly larger than the distal denticles at mid-crown (DSDI = 0.92). Both mesial and distal denticles are chisel-shaped, sub-quadrangular at the base, and longer mesiodistally than wide baso-apically along the carina. Denticles from both the mesial and distal carinae are inclined apically and their external margin is symmetrically convex. The mesiodistal main axis of the denticles is orthogonal to both mesial and distal margins. The interdenticular space is narrow and interdenticular sulci are present between both mesial and distal denticles.

The enamel surface texture is irregular. IIPG-08 and IIPG-09 show transverse undulations and a single marginal undulation, respectively, at mid-crown, adjacent to the distal carina, on the labial surface.

Morphotype III : IIPG-01, -04, -05, -06, -10, -12 ( Fig. 4 View Fig ), and possibly IIPG-11. The crowns are characterized by an important labiolingual compression (CBR <0.5; Table 1) and a weak apicobasal elongation (CHR ≤ 2). The mesial margin is strongly convex apico-basally and labiolingually, whereas the distal margin is straight (IIPG-06, -10, and -12) to strongly concave (IIPG-01, -04, and -05) in lateral view. Both labial and lingual surfaces are slightly mesiodistally convex ( Fig. 4 View Fig ). The crown bears well-developed carinae on the mesial and distal margins. The mesial carina is centrally positioned on the mesial margin of some teeth (IIPG-04, -05, -10, -12), and slightly curved lingually towards the base in other crowns (IIPG-01 and IIPG-06; Fig. 4 View Fig ). The denticulated carinae reach the base of the crown, and even extend well-beneath the cervix in some teeth (IIPG-05 and IIPG-06). The distal carina is either straight or strongly bowed labially. The cross-sectional outline of the crown at the cervix is lenticular to lanceolate ( Fig. 4 View Fig ).

The denticle density of the mesial carina ranges from 12–15 denticles per 5mm at the apex, 12–14 denticles at mid-crown, and 15–21 denticles at the crown base. The distal carina bears 11–14 denticles per 5 mm close to the apex, 11–15 denticles at mid-crown, and 15–17 denticles per 5 mm basally. As seen in the two previous morphotypes, the denticles densities increase gradually basally in both mesial and distal carinae. With a DSDI ranging from 0.84–1.15, the mesial denticles at mid-crown are slightly larger to similar in size than the distal denticles. Both mesial and distal denticles are chisel-shaped, apically inclined, and their external margin is symmetrically convex. They are sub-quadrangular at the base and longer mesiodistally than baso-apically along the carina. The interdenticular space is narrow and no interdenticular sulci appear to be present between the denticles.

As in the other two morphotypes, the enamel surface texture is irregular and no marginal undulations, transverse undulations, flutes, longitudinal grooves, or ridges can be seen on the crown.