Albanerpeton sp.

Folie, Annelise & Codrea, Vlad, 2005, New lissamphibians and squamates from the Maastrichtian of Haţeg Basin, Romania, Acta Palaeontologica Polonica 50 (1), pp. 57-71 : 58-61

Albanerpeton sp.

Fig. 2 .

Material.—PSMUBB V 180–V 194 (15 incomplete premaxillae), V 195–V 215 (21 incomplete maxillae), V 216–V 272, V 279–V 302 and V 306 (82 incomplete dentaries), V 273–V 278 and V 303–V 305 (nine indeterminate jaw fragments), V 307–V 316 (10 incomplete frontals), V 317–V 327 (11 incomplete humeri), V 328–V 333 (six incomplete atlantes), V 334–V 339 (six axes) and V340–V352 (13 incomplete post−cervical vertebrae).

Description.—The isolated premaxillae discovered at Pui Islaz are robust. The best−preserved specimen ( Fig. 2A ) is a 2.2 mm high left part that bears eight loci for teeth. None of the premaxillae is medially fused. A well−developed dorsoventral medial flange forms a “tongue−in−groove” articulation between the paired premaxillae. The entire labial side of the pars dorsalis is slightly ornamented by pustules and anastomosed ridges and is perforated by a few foramina. The dorsal border of the pars dorsalis is straight but the bone is complete and presents a boss (sensu Gardner 1999a and 2000a) that covers one−third of the pars dorsalis and is ornamented by polygonal pits enclosed by ridges. It is separated from the rest of the process by a ventral rim. In lingual view, the elliptical suprapalatal pit is set just over the pars palatinum and communicates with the pars dentalis by a short canal. The suprapalatal pit is bordered by two well−developed internal supports. The bases of these supports are located on the pars palatinum and converge dorsally just over the suprapalatal pit. On some specimens, an additional pit is present ventromedially to the suprapalatal pit. This foramen is also linked to the pars dentalis by a short canal.

The best−preserved maxilla ( Fig. 2B ) is a 3 mm long right specimen whose posterior part is broken off. This maxilla possesses 14 loci for teeth. By comparisons with complete figured material (e.g., Gardner 1999a: pl. 1M), it seems that a complete maxilla of Albanerpeton sp. from Pui Islaz was around 4.2 mm long. The lateral process, which articulated with the premaxilla, is short. In lingual view, the pars dentalis is straight. The anterior part of the pars palatinum is wide, but it progressively becomes narrower posteriorly. Labially, the pars facialis thins posteriorly. Its surface is rather smooth, except the presence of a few foramina in the anterior region. The junction between the lateral and nasal processes of the premaxilla forms the inferior and posterolateral margins of the external naris.

1 Emended from Albanerpeton nexuosus Estes, 1981 , in order to retain the conformity of the generic and specific genders (ICZN, Article 34.2).

2 Emended from Albanerpeton gracilis Gardner, 2000 , in order to retain the conformity of the generic and specific genders (ICZN, Article 34.2).

The dentaries ( Fig. 2C ) are robust and are similar to those described elsewhere for albanerpetontids (see, e.g., Gardner 2000b: fig. 3L–P). An association between some of the Pui Islaz fragments indicates that the dentaries probably reached a length of around 6 mm. Anterior prominences correspond to the intermandibular joints between paired dentaries. The labial side of the bone appears rather low anteriorly, but progressively becomes higher rearwards to the level of the Meckelian canal opening. It is perforated by only one row of foramina and some small additional foramina are concentrated in the anterior part of the bone. The posterior part of the bone, against which the postdentary bone was attached, is not preserved in the available material from Pui Islaz. The dorsal edge of the dental parapet is straight and rather high. On the ventral side of some specimens, a large ridge marks the insertion area for intermandibular muscles. In lingual view, the Meckelian canal is closed. The dental shelf is low, straight and gutter−shaped. Teeth are pleurodont, non−pedicellate, straight, closely packed and not highly heterodont, with crowns that are labiolingually compressed, faintly tricuspid and chisel−like.

The frontals are usually very fragmentary in the Pui Islaz material. They are rather flat but the area between the ventrolateral crests is dorsally concave. Polygons and ridges ornament their dorsal surface. The best−preserved frontal ( Fig. 2D ) is 2.5 mm long, but it is incomplete: only the area between the two ventrolateral crests in the anterior part of the frontal, the anterior part of the right ventrolateral crest, a small part of the left ventrolateral crest and two small foramina at the top of the crests are preserved. The ventrolateral crests are triangular in cross−section and appear rather slender but their external parts are missing and they were probably wider. The anterior portion of the frontal is unfortunately always broken off in the Pui Islaz material, so that it is not possible to determine the structure of the anterolateral or internasal processes. Although it is not possible to know the original length of the frontals, the angle between the ventrolateral crests is wide and it is likely that the frontals were characteristically triangular.

Ten distal ends of humeri have been discovered in the investigated lens at Pui Islaz (one of which is illustrated in Fig. 2E ). The shaft is straight and the humeral ball is spherical. The ulnar epicondyle is smaller than the radial epicondyle.

The atlas ( Fig. 2F ) is anteroposteriorly compressed. In anterior view, it bears two wide kidney−shaped cotyles, separated by a gutter−like odontoid process. Only the bases of the neural arches are preserved. The axis ( Fig. 2G ) is conical in shape and approximately 1 mm long. Dorsally, it bears a semicircular projection that articulated with the atlas (Estes and Hoffstetter 1976).

Some fragments of trunk or caudal vertebrae have also been found in the material from Pui Islaz. These pieces are characteristically hourglass−shaped, amphicoelous (sensu Estes and Hoffstetter 1976; Duffaud 2000), and widened in their medial part to form two lateral areas. None of the vertebrae are complete.

Discussion.—Each kind of bones presents the same morphology (e.g., premaxillae are robust and the suprapalatal pits share the same characteristics). The entire albanerpetontid material likely belongs to a single taxon.

The distal ends of humeri found at Pui Islaz are characteristic for the family Albanerpetontidae . In other Amphibia, the shaft is more widened, the distal part is wider, the humeral ball is moved aside and distally flattened, and the ulnar epicondyle is wider than the radial one ( Gardner and Averianov 1998; Gardner 1999b).

The vertebrae also display characteristic albanerpetontid morphology: the two first vertebrae (with partially the first trunk vertebra) are specialised to add an atlanto−axial joint that allows movement in a mediolateral plane ( McGowan 1998; Gardner 2001). The original diagnosis of A. inexpectatum is mainly based on the fusion of the first three vertebrae (Estes and Hoffstetter 1976). However, Gardner (1999a, b) showed that this character is only diagnostic at the familial level and gave a more accurate diagnosis of A. inexpectatum based on other features.

McGowan and Evans (1995) showed that the shape of the frontals is diagnostic at the generic level. Although incomplete, the specimens discovered at Pui Islaz are likely triangular and are thus characteristic of the genus Albanerpeton , whereas Celtedens and Anoualerpeton have a more rectangular frontal ( Gardner 2000b; Gardner et al. 2003). Venczel and Gardner (2003) recently identified a new Albanerpeton species that, e.g., bears a unique ventromedial keel on the frontals. As our specimens do not bear any keel, they cannot belong to this new species.

With the exception of the basalmost species A. arthridion , the morphology of the premaxilla allows to group species of Albanerpeton into two great clades ( Gardner 2002). These clades probably separated during the latest Albian– earliest Cenomanian ( Gardner 1999 c, d, 2002). In one clade, A. galaktion , A. gracile , and A. cifellii are characterised by gracile−shaped premaxillae with a triangular suprapalatal pit. On the other hand, the premaxillae discovered at Pui Islaz are particularly robust and their suprapalatal pit is elliptical, like in the clade including A. nexuosum and A. inexpectatum ( Gardner 1999a, 2000a).

The size of the suprapalatal pit on the premaxillae from Pui Islaz can be evaluated around 7% of the lingual side of the pars dorsalis. It is closer to the condition observed in Albanerpeton inexpectatum (4–7%, Gardner 1999a) and differs from the sizes (9–13%) observed in A. nexuosum ( Gardner 2000a) . Attribution of the Pui Islaz material to the Aptian–Albian species A. arthridion can be excluded, because its suprapalatal pit represent only 1% of the lingual side of the pars dorsalis. With the proportion of the suprapalatal pit, the second argument that prevents the attribution of the Pui Islaz material to A. nexuosum is the heterodonty of dentary teeth. Those of A. nexuosum are distinctly higher and wider in the anterior part of the bone.

The general shape of the albanerpetontid material from the Pui Islaz site is concordant with A. inexpectatum . In his revision of A. inexpectatum, Gardner identified 5 autapomorphies for this species ( Gardner 1999a): pustulate ornamentation on the labial side of the premaxilla; maxilla and dentaries of large individuals weakly ornamented labially; dentary with a low dorsal process that contributes to coronoid process; azygous frontals broad with a equilateral triangle form; and wide ventrolateral crests, deeply concave dorsally in the orbital region. The ornamentation with pustules and ridges is present on the entire labial side of the premaxillae from Pui Islaz even if bones are worn ( Fig. 2A 2 ). Maxillae and dentaries are unornamented but the Pui Islaz specimens are likely not large ( Fig. 2B 2, C 2 ). As mentioned in the description, the posterior part of the bones is not preserved, it is therefore not possible to observe the coronoid process. It is likely that the frontal was triangular and the angle between the ventro−lateral crests is wide so that it is supposed that the shape of the frontal was close to an equilateral triangle ( Fig. 2D ). The ventrolateral crests are not entirely preserved but they were probably broad. The orbital region of the bone is missing so that it is not possible to observe the deep concavity of the crests.

Albanerpetontid material was previously known from several localities in Europe: middle–late Campanian of La Neuve, France; late Campanian of Laño, Spain;?early Maastrichtian of Cruzy, France; late Maastrichtian of Cassagnau, France and late Maastrichtian of various localities in the Haţeg Basin ( Duffaud 2000). Duffaud (2000) attributed all these specimens to a single species. Because of the presence of a boss on the dorsal part of the premaxilla and of the ornamentation of the bone that is stronger is the upper part than in the lower part, he identified this taxa as being close to A. nexuosum . The new albanerpetontid material found at Pui Islaz differs from the material described by Duffaud (2000) by the pars dentalis that is more laterally projected ( Fig. 2A and Duffaud 2000: fig. 1). However, both the material from Pui Islaz and material described by Duffaud seems to belong to the same taxa. The presence of the boss on the dorsal bor− der of the premaxilla prevents the attribution of this taxa to A. inexpectatum but the characters observed on the Pui Islaz material indicate that the Late Cretaceous albanerpetontid species was nevertheless closer to this species than to A. nexuosum as concluded by Duffaud (2000).

It is clear that the material discovered at Pui Islaz is not sufficient to assign it to A. inexpectatum . Nevertheless, the Pui Islaz material seems to be closer to this species than to all the other species of the genus Albanerpeton . The characters that are non−concordant with A. inexpectatum or that are unknown on the Pui Islaz material, are not sufficient to erect a new species. Moreover, this taxon was previously described from Miocene sediments, while the site of Pui Islaz is Maastrichtian in age. If the taxonomic assignment is confirmed, the temporal range of A. inexpectatum would extend over more than 40 millions years. Such exceptional longevity is suspected in another albanerpetontid species, Celtedens megacephalus , which is known from the Late Jurassic to the Albian of Western Europe ( Gardner 2002; McGowan 2002).

Figures

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.