Denisodon moroccensis, Hahn & Hahn, 2003

Hahn, Gerhard & Hahn, Renate, 2003, New multituberculate teeth from the Early Cretaceous of Morocco, Acta Palaeontologica Polonica 48 (3), pp. 349-356 : 352-355

Denisodon moroccensis sp. nov.

Figs. 1B , 3A–E .

Derivation of name: After Morocco, where the species was found. Holotype (monotypy): The isolated m2 MNHN SA 97 .

Type locality: Anoual Syncline , eastern High Atlas, Morocco .

Type stratum: Early Cretaceous (?Berriasian).

Diagnosis.—As given for the genus.

Description

Measurements.—Length = 1.0 mm; width = 1.2mm; height of crown (at l1) = 1.2 mm.

Preservation.—Crown well preserved. The buccal cusp and the central basin are distinctly eroded. Both roots are broken. Crown separated from the roots by a distinct furrow.

Orientation.—The tooth is a right m2as is shown by com − parison with the m2 of Hahnodon and the Paulchoffatiidae .

Occlusal view ( Fig. 3A ).—Crown somewhat hour−glass shaped, well rounded in front and behind. Lingual wall only slightly indented between the anterior and posterior cusps. Anterior half of the crown occupied by two large cusps, b1 and l1, closely attached to each other. Longitudinal valley between them narrowed to a slight furrow that fades on the anterior slope of the crown. Apex of both cusps placed posteriorly, with the anterior flank sloping down at 45°, but with the posterior flank sloping down nearly vertically. b1 larger than l1, slightly eroded only on its apex. l1 not composed of two confluent cusps, distinctly eroded at its apex and posterior wall. Both lateral flanks of l1 and anterior flank of b1 covered with some weakly indicated wrinkles of enamel, but without ridges as is characteristic of the Paulchoffatiidae . Posterior half of the crown occupied by a deep basin, surrounded by a raised border with three elevations. First elevation placed posterobucally, interpreted here as the rudimental cusp b2. Second elevation placed in the posterobuccal corner of the crown, being only a very small peak of the border. It either is a last remnant of cusp b3 or only a slight bump of the border. Third elevation placed in the posterolingual corner of the crown, expressed as a relatively large, but low swelling, projecting somewhat into the central basin and having been partly demolished by erosion. It can, in comparison with Hahnodon , be interpreted as cusp l3. Flanks of b2and l3 covered with some weakly expressed enamel ridges. Central basin flat, without cusps, cuspules or bars (as in Paulchoffatiidae ), but with traces of erosion in its center.

Buccal view ( Fig. 3B ).—Cusp b1 high and pointed apically, marking the highest point of the crown. Anterior wall well rounded, posterior wall sloping down vertically. Cusp b2low in comparison with b1, pointed, well defined. Buccal border of the crown again somewhat elevated close to its posterior corner, marking the position of cusp?b3. Posterior border low, indistinct, ascending lingually to cusp l3. Wrinkling of the enamel on b1 distinct.

Lingual view ( Fig. 3C ).—Cusp l1 distinct, with eroded apex, less high than cusp b1. Anterior and posterior flank sloping down in the same degree as on cusp b1. Lingual border of the central basin low, raised again posteriorly to cusp l3, which is only 1 / 3 as high as cusp l1. Enamel of the buccal wall on l1 smooth, wrinkles confined to the anterior wall of this cusp.

Anterior view ( Fig. 3D ).—Both cusps, l1 and b1, steeply arising from the base of the crown. Apex of b1 somewhat rounded by wear, apex of l1 distinctly eroded, flat. Vertical furrow between l1 and b1 narrow and short, confined to the upper half of the crown. Wrinkling of the enamel visible on both flanks of b1 and on the outer flank of l1. Base of the crown ascending somewhat from the buccal side to the lingual side, with a blunt spur at the base of the lingual flank. No pressure mark visible on the anterior wall of the crown.

Posterior view ( Fig. 3E ).—Apices high and well rounded, on b1 flat and deeper on l1. On b1 erosion confined to two small ovoid marks at the apex and on the posterior wall, on l1 posterior wall more strongly eroded with the dentine partly exposed. Furrow between l1 and b1 short and indistinct. Posterior border of the crown inclined somewhat to the buccal side, raised distinctly on the lingual side to cusp l3 which shows a small notch in its posterior wall. Cusp b2very low, but distinct at the base of b1, cusp?b3 marked as a gentle undulation of the buccal border. Distinct wrinkling of the enamel on the outer wall of b1. Posterior wall of the crown somewhat higher buccally than lingually. No pressure mark visible on the posterior wall of the crown.

Hahnodontidae , gen. et sp. indet.

Besides the holotype of Denisodon moroccensis , two other multituberculate teeth are present. It cannot be decided whether they belong to Hahnodon or Denisodon . Therefore, they are described here under open nomenclature.

Posterior upper premolar (P3 or P4), MNHN SA 152 Figs. 4A–D , 5A .

Description

Measurements.—Length of fragment = 0.7 mm; width = 1.0 mm; height of crown = 0.9 mm.

Preservation.—Preserved is only the posterior portion of the tooth. Both roots are broken.

Orientation.—Present is the posterior portion of a left upper posterior premolar, as explained under “Discussion“.

Occlusal view ( Fig. 4A ).—Posterior border ovoid, with the lingual side somewhat more curved than the buccal side. Crown equipped with only one row of cusps which runs somewhat obliquely from the anterolingual to the posterobuccal side. Preserved portion of cusp row composed of three cusps, decreasing in size from front to behind. They are interpreted as cusps L3–L5 (see under “Discussion”). Cusps broader than long, with a broad, shelf−like area on both sides of the crown. All three cusps are connected by a longitudinally directed enamel ridge. The apex of the anterior cusp is broken. The apices of both other cusps are pointed and only slightly eroded. The enamel is damaged at both anterior corners of the crown and at the buccal flank of the first cusp.

Lingual view ( Fig. 4B ).—Preserved portion of the crown higher than long. Posterior wall curved convexly. Apex of anterior cusp broken. Apex of second cusp slightly rounded, as high as the anterior cusp, with some enamel ridges sloping up across the flank of the cusp. Third cusp distinctly smaller and lower than the other cusps, also with three enamel ridges. Posterior wall of the crown separated from the posterior cusp by a slight edge. Enamel damaged in a rounded area near to the anterior wall. Enamel of the lingual, buccal and posterior walls of the crown slightly wrinkled.

Buccal view ( Fig. 4C ).—Proportions of the crown as in lingual view, also shape and height of the cusps. Second cusps with two distinct enamel ridges. Posterior cusp also with few enamel ridges which split into few branches that cover the postero−buccal region of the wall. At the base of the third cusp the enamel is damaged.

Posterior view ( Fig. 4D ): Shape of crown roughly triangular, with the buccal wall more arched than the lingual wall. The three cusps are visible one above the other. Crown somewhat narrowed on both sides at its base against the root. Posterior wall of the crown covered with some indistinct enamel ridges.

Discussion.—The most diagnostic feature of the tooth here described is the presence of only one row of cusps on the preserved portion of the crown. Upper premolars with only one row of cusps are unknown among the Plagiaulacida , but premolars with a shortened buccal row are known. Therefore,

the present broken tooth can be interpreted best as the posterior portion of an upper premolar with only the posterior lingual cusps preserved. This interpretation is supported by the oblique course of the cusp row. A shortened buccal row of cusps is present in at least four families of the Plagiaulacida :

Paulchoffatiidae , Pinheirodontidae , Eobaataridae and Plagiaulacidae . In all these families the lingual row has four cusps and covers the whole crown longitudinally, whereas the buccal row has only two cusps which are confined more or less to the anterior half of the crown. The following taxa must be mentioned:

– P3 of Kielanodon hopsoni G. Hahn, 1987 (see G. Hahn 1969: text−fig. 65; G. Hahn 1987: text−figs. 7, 8; here Fig. 5B ). The P3 is relatively narrow and triangular in shape. Both the last lingual and buccal cusps are large. The second buccal cusp is located between the second and third lingual cusp. The fourth lingual cusp occupies the posterior portion of the crown alone. All cusps have coarse enamel ridges.

– P4 of the Pinheirodontidae ( Hahn and Hahn 1999b: text−fig. 59a, c; here Fig. 5C ). In contrast to K. hopsoni , the last lingual cusp is small, and the tooth is less narrowed posteriorly. The enamel ridges are less coarse than in Kielanodon .

– P4–5 of Eobaatar magnus Kielan−Jaworowska, Dashzeveg, and Trofimov, 1987 ( Kielan−Jaworowska et al. 1987: text−fig. 3b; here Fig. 5D ). The last lingual cusp is the largest of the row. On P4, a very small third buccal cusp is present, placed beside the anterior half of the fourth lingual cusp. On P5, only two large buccal cusps are present, the second placed beside the valley between the second and third lingual cusps.

–?P5 of Eobaatar hispanicus Hahn and Hahn, 1992 ( Hahn and Hahn 1992: text−fig. 5a). The structure of the crown is similar to that in E. magnus .

– P5 of Bolodon osborni Simpson, 1928 ( Kielan−Jaworowska et al. 1987: text−fig. 3A). Structure is also similar to that in Eobaatar .

As is shown by this compilation, a shortened buccal cusp row can be present on the P3 of the Paulchoffatiidae , the P4 of the Pinheirodontidae , the P5 of the Plagiaulacidae and the P4–5 of the Eobaataridae . Consequently, the tooth described here is either a P3 (compared with the Paulchoffatiidae ) or a P4 (compared with the Pinheirodontidae ), but surely not a P5, because this tooth carries three rows of cusps in these two families.

Moreover, the new tooth differs from all the discussed teeth by two details: 1) the unusal width of its posterior portion and 2) the presence of two posterior lingual cusps without buccal antagonists (which may be explained by the presence of five instead of four lingual cusps on MNHN SA 152). A similarly small last lingual cusp is present again only in the Pinheirodontidae . Thus, the tooth described here of the Hahnodontidae is characterized by a combination of features unknown in the other families. It is not clear whether this tooth belongs to Hahnodon or to Denisodon ; therefore it is grouped in open nomenclature.

Lower incisor, MNHN SA 102

Fig. 6A–D .

Description

Measurements.—Length of crown = 2.0 mm; height of crown ~ 1.2mm.

Preservation.—Only crown preserved, corroded postmortem by several small pits. The dorsal face has been strongly eroded by wear. The crown was completely covered by enamel.

Orientation.—Present is a right incisor, as is demonstrated by comparison with the Paulchoffatiidae (see G. Hahn 1969: text−fig. 24). The inner face of the crown shows a longitudinal enamel ridge, and the outer face has a rounded upper edge as in the Paulchoffatiidae .

Lateral view ( Fig. 6A ).—Crown stout, with a broad base. Dorsal border gently concave, curving upward at the tip. Ventral border strongly convex. Upper edge of crown rounded. External wall strongly arched convex. Tip strongly eroded. Enamel smooth.

Mesial view ( Fig. 6B ).—Longitudinal enamel ridge confined to the anterior half of the crown, dividing it into a narrower upper and a wider lower portion. Tip more pointed than on lateral side. Upper edge not rounded. Otherwise shape as in lateral view.

Dorsal view ( Fig. 6C ).—Tongue−like shape, nearly symmetrical. Enamel of dorsal face completely eroded, dentine exposed.

Anterior view ( Fig. 6D ).—Crown somewhat higher than broad, ovoid in shape. External wall well rounded; internal wall less arched, longitudinal enamel ridge distinct. Tip rounded.

Discussion.—The present incisor corresponds generally to those known from the Paulchoffatiidae (see under “orientation”). It is relatively short and stout with its crown distinctly bent upwards. In this it is most similar to some specimens of Kuehneodon dietrichi G. Hahn, 1969 (see G. Hahn 1978: pl. 3: 13a, b, pl. 4: 20a, b). But in Kuehneodon the internal wall of the crown is distinctly less arched as in the specimen described here (see G. Hahn 1978: pl. 2: 5c, pl. 4: 20a). In the Pinheirodontidae ( Hahn and Hahn 1999b: fig. 14a, b) and other families of the Plagiaulacida the crown of the incisors is longer, more slender and also more curved than in this specimen. With that, the Hahnodontidae remain in the structure of their incisors, on a primitive level similar to that in the Paulchoffatiidae .

Figures

Fig. 1. Comparision of left lower m2in Paulchoffatioidea superfam. nov. A. Hahnodon taqueti Sigogneau−Russell, 1991a; redrawn from Sigogneau− Russell, 1991a: fig. 2c. B. Denisodon moroccensis gen. et sp. nov. C. Kuehneodon sp.; redrawn from Hahn and Hahn 1998: fig. 39b. D. Pinheirodon sp.; redrawn from Hahn and Hahn 1999b: fig. 29c.

Fig. 3. Denisodon moroccensis gen. et sp. nov., right m2, holotype, MNHN SA 97, in occlusal (A), buccal (B), lingual (C), anterior (D), and posterior (E) views; in A anterior is up. Scale bar 1 mm.

Fig. 4. Hahnodontidae, gen. et sp. indet., left upper posterior premolar (P3 or P4), MNHN SA 152in occlusal (A), lingual (B), buccal (C), and posterior (D) views; in A anterior is up. Scale bar 1 mm.

Fig. 5. Comparison of upper right premolars with a shortened buccal row of cusps. A. Hahnodontidae, gen. et sp. indet., P3 or P4, posterior portion of tooth with the preserved posterior lingual cusps,?L3–5. B. Kielanodon hopsoni G. Hahn 1987, Paulchoffatiidae, P3. Redrawn from G. Hahn, 1987: text−fig. 8a. C. Pinheirodontidae, gen. et sp. indet., P4. Redrawn from Hahn and Hahn 1999b: fig. 59c. D. Eobaatar magnus Kielan−Jaworowska, Dashzeveg and Trofimov, 1987, Eobataridae, P5. Redrawn from Kielan− Jaworowska et al. 1987: text.−fig. 3B.

Fig. 6. Hahnodontidae, gen. et sp. indet., right lower incisor, MNHN SA 102, in lateral (A), mesial (B), dorsal (C), and anterior (D) views. Scale bar 1 mm.