Bicuspidon hatzegiensis, Folie & Codrea, 2005

Folie, Annelise & Codrea, Vlad, 2005, New lissamphibians and squamates from the Maastrichtian of Haţeg Basin, Romania, Acta Palaeontologica Polonica 50 (1), pp. 57-71 : 64-66

Bicuspidon hatzegiensis sp. nov.

Fig. 4A–D.

Holotype: PSMUBB V 368 , posterior part of a left dentary with two complete teeth ( Fig. 4C).

Type locality: Pui Islaz, Haţeg Basin, Transylvania, Romania, Europe.

Type horizon: Sânpetru Formation, Maastrichtian, Late Cretaceous.

Derivation of the name: After “Haţeg”, the name of the synorogenic basin in Romania where this new species was found.

Diagnosis.—Differs from B. numerosus in teeth bearing well−developed labial and lingual striae; and by having the posteriormost tooth only slightly smaller than the other ones, bearing a conical crown devoid of sharp and V−shaped transverse ridge.

Material.—PSMUBB V 366–V 374 (nine incomplete dentaries), V 375, V 376 (two incomplete maxillae), V 377–V 379 (three indeterminate jaw fragments), V 380 (one isolated tooth), V 381–V 384 (four?cervical vertebrae centra), V 385, V 386 (two?caudal vertebrae centra).

Description.—The jaw fragments are between 1.5 and 3.5 mm long with a mean of 2 mm and bear from 1 to 5 teeth. Bones and teeth are thick and robust. In labial view, the fragments bear a few aligned foramina and are smooth or ornamented by some longitudinal ridges, giving them some wooden aspect. In lingual view, subcircular replacement pits at the base of the teeth are present on some fragments ( Fig. 4A). The dentition is heterodont. Teeth are subpleurodont, closely packed and extend beyond the dental parapet for more than half of their height. At approximately three−quarters of their height, a constriction marks the separation between the root and the crown of the teeth. The crowns are circular to slightly elliptic in cross−section and ornamented by external vertical ridges ( Fig. 4B 1 ). In occlusal view, teeth are approximately 250 µm wide except for the fragment PSMUBB V 367 that is approximately 500 µm wide. Two morphotypes of crowns can be observed in the sample from Pui Islaz. The first is molariform, formed by two distinct cusps separated by a labiolingual V−shaped, transverse ridge ( Fig. 4B 2 ). From the wider labial cusps, one anterior and one posterior ridges extend lingually around the crowns, but do not reach the smaller lingual cusp. The second morphotype is conical and monocuspid. Both morphotypes are associated on the holotype (PSMUBB V 368): the anterior tooth has molariform crown, whereas the posterior one, which corresponds to the last dentary tooth position, is conical and monocuspid ( Fig. 4C). The molariform crown is slightly wider labiolingually and more compressed antero−posteriorly than the conical crown.

FOLIE AND CODREA—MAASTRICHTIAN LISSAMPHIBIANS AND SQUAMATES 65

lingual cusp labial cusp lingual cusp replacement pits Meckelian canal labial cusp lateral foramen small foramen molariform tooth conical tooth

Several incomplete vertebrae have been found on the site of Pui Islaz and are tentatively assigned to Bicuspidon hatzegiensis . All are procoelous. The cervical vertebrae ( Fig. 4D) are short and their dorsal side is perforated by two small foramina near the middle of their length. The neural arch is lost. The dorsal vertebrae are similar, but are more elongated and narrower than the cervical ones.

Discussion.—A heterodont dentition with transversely expanded teeth is similar to that occurring in the Polyglyphanodontinae ( Estes 1983). Among this clade Polyglyphanodon , Paraglyphanodon , Dicothodon , Peneteius , and Bicuspidon are five North American genera bearing transversely bicuspid and molariform teeth ( Nydam 1999; Nydam et al. 2000; Nydam and Cifelli 2002) whereas the Mongolian representatives of this family and the North American genus Haptosphenus Estes, 1964 (sometimes considered as a member of the Teiinae ; Gao and Fox 1996) have mono−, tri− or polycuspid teeth ( Gilmore 1943; Estes 1964; Sulimski 1975).

Polyglyphanodon and Paraglyphanodon (maybe a juvenile form of Polyglyphanodon ; Gilmore 1943; Nydam 1999) have medial and lateral cusps connected by a horizontal or U−shaped transverse ridge (instead of V−shaped in Bicuspidon ) and mediolaterally expanded teeth (instead of not expanded). Moreover, Polyglyphanodon appears to have suppressed tooth replacement, so that replacement pits cannot be observed ( Gilmore 1942; Nydam and Cifelli 2002). Similar to Bicuspidon numerosus , replacement pits are clearly visible on B. hatzegiensis sp. nov.

Peneteius Estes, 1969 bears maxillary teeth with a Vshaped transverse ridge, but these teeth also possess a more complex morphology with multicuspid crowns ( Nydam et al. 2000) whereas the tooth crowns in Bicuspidon are strictly bicuspid.

Dicothodon Nydam, 1999 is a Polyglyphanodontinae−like genus known in North America that bears V−shaped crowns. It differs from Bicuspidon by the presence of anterior and posterior ridges connecting the two cusps together and limiting two associated basins ( Nydam 1999).

The attribution of the fragments of Pui Islaz to the American genus Bicuspidon Nydam and Cifelli, 2002 is based on the presence of the following characters: teeth crowns not transversally expanded, formed by a labiolingual, V−shaped, transverse ridge and with anterior and posterior ridges lingually going around the tooth without contact with the smaller lingual cusp. However, the fragments show some differences with Bicuspidon numerosus . The posteriormost tooth crown is perfectly conical, without a transverse ridge or any additional cusps (instead of last tooth bicuspid with a small medial cusp near the lateral cusp), and bear some vertical external ridges (instead of internal crenulations). Moreover, except for the fragment PSMUBB V 367, the teeth are around half the size of those of Bicuspidon numerosus . These differences support the erection of the new species Bicuspidon hatzegiensis , to represent these specimens recovered from Pui Islaz.

To date, vertebrae have not been described for Bicuspidon . However, the vertebrae described herein are only tentatively referred to B. hatzegiensis because they closely resemble those of Polyglyphanodon ( Gilmore 1942) .

Lacertilia indet.

Genus and species indet. A

Fig. 5A.

Material.—PSMUBB V 389–V 391 (three nearly complete frontals).

Description.—The best−preserved frontal that can be referred to this taxon (PSMUBB V 390) is 2.7 mm long ( Fig. 5A). Its posterior part splits into two symmetrical branches, whose ends are broken off. The interorbital region is particularly narrow. The frontal widens out anteriorly into an oval and slightly dorsally concave plate. An open canal joins the anterior and posterior parts of the specimen. The frontal is not ornamented dorsally. The two other frontals are very similar, but lack the right branch of the posterior part and a great portion of the anterior part.

Discussion.—The proportions and the general shape of the first form closely resemble those of the gekkonid Rodanogekko Hoffstetter, 1946, from the Late Eocene of France (compare with Estes 1983: fig. 14D). In other Gekkonidae , the interorbital region is distinctly wider. However, the dorsal surface of the frontal is ornamented by anastomosing ridges in Rodanogekko, although PSMUBB V 390 is completely smooth. Moreover, the processus descendens of the frontal meet medially its counterpart in Gekkonidae ( Estes 1983) , whereas they approach, but do not meet on PSMUBB V 390. These specimens cannot be attributed to any of the taxa identified at Pui Islaz, because most Scincomorpha are characterised by two wide coossified frontals that are rectangular in shape whereas PSMUBB V 390 is azygous and narrow (e.g., Estes 1983: fig. 15).

Figures

Fig. 1. The outcrop (Pui Islaz, indicated by a star) attributed to the Maastrichtian Sânpetru Formation, is located in the Bărbat River bed south of the village of Pui. The grey areas indicate the sedimentary basins (I, Rusca Montana Basin; II, Strei Basin; III, Haţeg Basin; IV, Petrosani Basin). Modified from Codrea et al. (2002).

Fig. 2. Albanerpeton sp. A. PSMUBB V 180, left premaxilla in lingual (A1) and labial (A2) views. B. PSMUBB V 195, right maxilla in lingual (B1) and labial (B2) views. C. PSMUBB V 237, left dentary in lingual (C1), labial (C2), and occlusal (C3) views. D. PSMUBB V 308, small fragmentary frontal in ventral (D1) and dorsal (D2) views. E. PSMUBB V 317, distal end of a left humerus in ventral view. F. PSMUBB V 328, atlas in anterior view. G. PSMUBB V 334, axis in dorsal view. SEM migrographs.