Albanerpeton inexpectatum Estes & Hoffstetter, 1976

Vasilyan, Davit, Cernansky, Andrej, Szyndlar, Zbigniew & Moers, Thomas, 2022, Amphibian and reptilian fauna from the early Miocene of Echzell, Germany, Fossil Record 25 (1), pp. 99-145 : 99

Albanerpeton inexpectatum Estes & Hoffstetter, 1976

Fig. 2

Material and horizon.

One frontal HLMD-Ez 2004, four praemaxillae HLMD-Ez 2005-2008, nine maxillae HLMD-Ez 2009-2016, ten dentaries HLMD-Ez 2017-2027, one vertebra HLMD-Ez 2028.

Description.

Frontal: Frontal is partly preserved. It is triangular in shape and as wide as long (Fig. 2A ). The entire preserved dorsal surface of the bone is covered by moderately deep polygonal pits limited from each other by rather low ridges. The anterolateral processes are missing. The anteriorly-projecting internasal is rather narrow and elongated. In ventral view, its spike-like outline is more evident (Fig. 2B ). Only the anteromedial slot is preserved. It is long, low and not deep. In ventral view, the ventrolateral crest is broad, concave and in transverse view, triangular in outline. It starts at the base of the preserved portion of the anterolateral process and projects posterolaterally, reaching the posterior lateral tips of the frontal. The crest becomes thinner laterally. The ventral surface of the frontal, between the posterolateral crests, is flat.

Praemaxilla: Available four praemaxillae show different preservation and are not fused. The medial surface of the bone, where two praemaxillae connect with each other, possesses grooves and flanges (Fig. 2G ). The width of the bone, measured along the tooth row, ranges from 1-1.5 mm. The pars dorsalis is elongated and long. In lateral view, it is curved. The laterodorsal notch is weakly developed. The pars dorsalis at its middle part extends slightly laterally, which in large-sized bones is stronger developed than in the small-sized ones. The labial surface of the bone is covered by different structures (Fig. 2C, F ). The ventral portion, corresponding to the pars dentalis, is nearly smooth. The middle part of the surface, making the most of the pars dorsalis, is pierced by nutrition foramina. The tip of the pars dorsalis possesses the boss. Pustular structures and polygonal-shaped pits cover it. In labial view, the maxillary process of praemaxilla projects laterally behind the pars dorsalis. In lingual view, the well-developed suprapalatal pit at the medial base of the pars dorsalis is present (Fig. 2D, H ). It has an elongate outline and reopens ventrally as a palatal foramen in the ventral surface of the pars palatinum. In medial view, the pars palatinum is curved. Distinct vomerine and maxillary processes are visible on the pars palatinum. The maxillary process is stronger developed than the vomerine one. Six to seven pleurodont teeth are attached to the pars dentalis.

Maxilla: In total, eight maxillae with different preservation are available. The pars dentalis in most well-preserved specimens possesses 13-14 teeth or tooth bases. In lingual view, the pars dentalis is high anteriorly and reduces in height posteriorly (Fig. 2J, M, P ). The pars palatinum is well-developed and curved. In the middle part of the bone, it reaches its most width. The anterior tip of the pars palatinum extends anteromedially and forms a distinct process (Fig. 2J, P ). The premaxillary process is well developed (Fig. 2M, P ). The distinct nasal process projects anterodorsally (Fig. 2J, M ). Both the dorsal and labial surfaces of the maxillae are pierced by short rows of up to three nutrition foramina, which are limited to the area around the nasal process (Fig. 2N, L, Q ).

Dentary: All eleven dentaries are only partially preserved. No dentary with a fully preserved tooth row (pars dentalis) is available in the material to count the tooth number. The teeth reduce in height posteriorly. The Meckelian groove is closed and form a canal. The dental shelf is moderately broad, and its lingual margin is angular (Fig. 2R, V ). The symphyseal articulation surfaces are flat and vertical. Lingually, it possesses two distinct prongs (Fig. 2R, S ). The dorsal prong is long and oriented anterodorsally. The ventral one is smaller and anteroventrally oriented. The ventral prong and the main symphyseal surface are separated with a moderately deep depression, which is pierced by the anterior opening of the Meckelian groove. The latter opens posteriorly with two large ventral and small dorsal ("opening for an unnamed canal" sensu Szentesi et al. (2015); fig. 8) openings. Taking into account the “natural” cross-sections of the bones (Fig. 2U, X, Z ), the split of the Meckelian canal into two branches already at the sixth tooth position can be stated. The small dorsal branch runs below the tooth row, whereas the large ventral one is enclosed in the ventral portion of the bone. The labial surface of the dentary is smooth. A row of labial foramina of different sizes is arranged along the midline of the dentary (Fig. 2T, W, Y ).

Dentition: The teeth on premaxillae, maxillae. and dentary have similar morphology. All teeth are pleurodont and closely located. The tip of teeth is tricuspid with a main central large cuspid and two lateral small cuspids, which are sometimes nearly absent. The tooth pedicles are compressed anterodorsally. The tooth tip is round in cross-section. They reduce in size posteriorly.

Remarks.

The fossil remains can be assigned to the genus Albanerpeton considering the presence of the following autapomorphies ( Venczel and Gardner 2005): 1) dorsal/ventral outlines of fused frontals are triangular (Character state 21(1) in Venczel and Gardner (2005)); 2) ratio of midline length of fused frontals to the width across posterior edge of bone, between lateral edge of the ventrolateral crest, is as wide as long (1:1) (Character state 22(1) in Venczel and Gardner (2005)); 3) path followed by canal through pars palatinum in praemaxillae, between dorsal and ventral openings of palatal foramen, is vertical (Character 27(1) in Venczel and Gardner (2005)). Among the species of the genus, two apomorphies of A. inexpectatum are such as; 1) the pustular ornament pattern of labial surface of premaxillary (Character 8(1) in Venczel and Gardner (2005)) and 2) form of ventrolateral crest on large, fused frontals wide and triangular in transverse view, with strongly concave ventral surface (Character 24(2) in Venczel and Gardner (2005)). Further, two character states [16(1), 17(1)] of Venczel and Gardner (2005) cannot be observed due to poor preservation of the material. The Echzell remains can be clearly distinguished from the second available European Tertiary albanerpetontid species Albanerpeton pannonicum by: 1) lack of the ventromedial keel on frontals (vs. present in A. pannonicum ); 2) labial pustulate ornament on premaxilla is not restricted to the boss but also cover the surface of the bone ventrally from the boss. The presence of boss on praemaxilla has been suggested as a characteristic for A. pannonicum and should be absent in A. inexpectatum (e.g., Venczel and Gardner 2005; Szentesi et al. 2015). The structures on the dorsolabial surface of the pars dorsalis on the studied material is interpreted as boss and most probably, suggesting the character to be shared between two species.

Figures

Figure 2. Albanerpeton inexpectatum from the Echzell locality. Frontal (A, B. HLMD-Ez 2004). Premaxillae (C-E. HLMD-Ez 2161; F-I. HLMD-Ez 2005). Maxillae (J-L. HLMD-Ez 2009; M-O. HLMD-Ez 2010; P, Q. HLMD-Ez 2012). The bones are figured in (A, K) dorsal, (B) ventral, (C, F, L, N, Q, T, W, Y) labial, (D, E, H, J, M, O, P, R, V, AA) lingual, (I) ventroposterior, (S, X) medial, (G, U, Z) posterior views. Where not indicated, the scale bar equals 5 mm.