Palaeocordylus bohemicus Roček, 1984

Čerňanský, Andrej, 2012, The oldest known European Neogene girdled lizard fauna (Squamata, Cordylidae), with comments on Early Miocene immigration of African taxa, Geodiversitas 34 (4), pp. 837-848 : 840-843

aff. Palaeocordylus bohemicus Roček, 1984 ( Figs 2-5 )

LOCALITY AND HORIZON. — Merkur-North opencast mine; Lower Miocene (Eggenburgian), Lower Orleanium, zone MN 3a.

MATERIAL EXAMINED. — Right dentary (Ah-1088 SGDB).

DESCRIPTION

Dentary

This is a long, ventrally straight bone ( Fig. 2 ), with a slight medial curvature at its anterior end. The symphysial facet is small and square-shaped. In transverse section, the dentary is C-shaped with a smooth external surface. This surface is pierced by five labial foramina (foramina pro rami nervorum alveolarium inferiorum). The maximum width of the dentary occurs at the posterior end. There is a prominent coronoid process (processus coronoideus), which is distinctly elongate and slants posterodorsally with its dorsoposterior limit being higher than the apices of the largest mandibular teeth. This dentary bears up to 25 bicuspid teeth (three tooth sockets and 22 preserved teeth present in Ah-1088 SGDB). There is a relatively long nontoothed portion of the dentary posterior to the last tooth. The lingual surface of the bone shows a deep and open groove for Meckel’s cartilage. However, its anterior portion is quite narrowed and it is shallower in this part. The horizontal lamina (lamina horizontalis) is straight and thick, especially in the anterior region, with a rounded medial margin. It gradually becomes thinner towards the posterior end as a result of the presence of the facet for the splenial on its ventromedial surface. The splenial facet turns on the ventral surface of the horizontal lamina and continues anteriorly up to the level of the 13 rd tooth. At the level of the 10 th tooth, the well-defined splenial facet on the medial surface of the ventral margin (crista ventralis) also begins. Posteriorly behind the splenial facet, a distinctive coronoid facet is developed on the horizontal lamina and, anteriorly, it rises at the level of the 21th tooth position. The opening of the alveolar canal is small and it lies at the level of the 19th tooth. The intramandibular septum, lying ventromedially from the alveolar canal, has a free posteroventral portion ( Figs 2 ; 3 ). A sulcus dentalis is present; it is narrow, but well developed along the tooth row, especially in the middle portion of the dentary.

Dentition

The dentition is pleurodont. The teeth are middle sized and blunt, typically bicuspid with cuspis labialis and cuspis lingualis ( Fig. 4 ). Teeth are labially attached to the dental parapet almost over their entire length, with only the tooth crowns rising above the parapet. The teeth are closely distributed. The sizes of the inter-dental gaps are very small. The tooth necks are more or less swollen lingually ( Fig. 5 ). Resorption pits are present on the lingual sides of some tooth bases. In the anterior portion of the dentary, the teeth are relatively smaller. The labial surface of the teeth is smooth. A pattern of striations has developed on the lingual surface of the tooth crown between the culmen lateralis anterior and culmen lateralis posterior (terms after Richter 1994). They begin below the tip of the tooth on the antero- and posterolabial portions of the tooth surface and run down, becoming less distinctive on the lowermost region of the tooth crown without joining each another. There are about six striae on the lingual side and these converge apically. The morphology of the tooth crowns is similar to that of the recent species Cordylus cataphractus Boie, 1828 (see Kosma 2004: pl. I., figs 4-6; however this taxon has a lot of other differences).

REMARKS

The Cordylidae , Scincidae Gray, 1825 and Paramacellodidae Estes, 1983 are highly related groups ( Evans & Chure 1998). The attribution to the family Cordylidae is beyond doubt, based on the combination of the following features: 1) the Meckelian canal is narrow to its anterior termination, but fully opened. The tendency toward closure of the Meckelian canal could be a characteristic of Scincidae as many scincid lizards show a closed Meckelian canal, in contrast to cordylids, which all have an open Meckelian canal ( Augé & Smith 2009); 2) the crista ventralis is straight in lateral view (after Lang 1991). However, some scincids also have a straight ventral border of the dentary ( Augé & Smith 2009); 3) the sulcus dentalis is well developed; and 4) the high number of blunt and conical anteroposteriorly compresed teeth with well developed lingual cusps and the presence of lingual striae on the crowns. The presence of the lingual cusp is more common among the cordylids than the scincids ( Folie et al. 2005).

The dentary is basically identical with the species described by Roček (1984) as Palaeocordylus bohemicus from the younger deposists of the Dolnice locality near Cheb (MN 4). However, there are also some differences: 1) in the holotypic dentary DP FNSP 97, the splenial facet on the horizontal lamina and also on the ventral margin reaches anteriorly to the level of the 9 th tooth position. On the dentary described herein, the splenial facet reaches the level of the 13rd tooth on the horizontal lamina and the10 th tooth level on the ventral margin of the dentary; 2) the external surface of the dentary from Merkur-North is pierced by five articulation intramandibular septum mental foramina, which is in contrast to holotypic dentary, where the row of foramina reaches seven. Given typical intraspecific variation in this characteristic among lizards (Klembara pers. comm.), I consider this characteristic to be insignificant;

striae culmen anterior cuspis labialis cuspis lingualis culmen lateralis posterior and 3) the striations are not so distinctly developed, with less striae than in the material from Dolnice (see Roček 1984: pl. I., figs 2-5; pl. II., fig. 1; where-in the number of striae in the dentary teeth is around 8 instead of 6). However, this is variable feature and therfore conveys only informative value. The number of striae in e.g., Cordylus cataphractus varies between individuals ( Kosma 2004). The number and arrangement of the striae also vary within the tooth row of a single individual in the material described by Kosma (2004) as in Bavaricordylus ornatus . Although the labial surface of the teeth is smooth in the dentary described herein, this feature can also vary. Although the striation can be well-developed in the Dolnice material, it can also exist to a lesser degree on the labial surface ( Roček 1984).

All these quoted differences could be caused by ontogenic changes and intraspecies variability. The total antero-posterior length of the dentary described here is 10 mm which is much less then the dentary described by Roček from Dolnice (the holotype DP FNSP 97 – section of the left dentary with a 19 tooth position is 14,8 mm, even with the most posterior portion broken away). For this reason, the dentary from the Merkur – North locality could represent a juvenile ontogenetic stage of developement. Because of a lack of knowledge of variations during ontogeny in the Lower Miocene cordylids due to such limited material, it is better to atribute this material to aff. Palaeocordylus bohemicus , because of its similarity.

COMPARISON

Although the taxonomical validity of the genus Bavaricordylus remains problematic, I have compared the material described here with the material attributed by Kosma (2004) and Böhme (2010) to this taxon.

The material of cordylids described herein differs from the Petersbuch 2 material described by Kosma (2004) as a new taxon – Bavaricordylus ornatus (MN4a) in the following features: 1) the tooth crowns of the Petersbuch 2 material possess a more striking pattern of striations with 20 distinct striations on the lingual surfaces of the tooth crowns and weak striations on their labial surfaces; Kosma 2004); 2) the culmines lateres of the Petersbuch 2 material are prominent and

The oldest known European Neogene girdled lizard fauna their ventral portion reaches the tooth shafts; and 3) the labial surface of the Petersbuch 2 dentary shows rough facets for the attachment of osteoderms.

The cordylid material described herein differs from that of Puttenhausen B described by Böhme (2010) as Bavaricordylus molassicus in the following features: 1) the dentary from Puttenhausen B is more robust; 2) the crista ventralis of the dentary from Merkur-North is straight whereas it is curved in that from Puttenhausen B; 3) the number of striae is up to 12 in the material from Puttenhausen B ( Böhme 2010); and 4) Puttenhausen B material has more anteriorly attached splenial; at the level of the 7 th tooth position ( Böhme 2010).

The material of indeterminate cordylids from the Korneuburg Basin located in Obergänserndorf, Austria is fragmentary, and this makes comparison with other specimens extremely difficult. The horizontal lamina is more robust in the dentary described herein compared to the dentary material described from this locality by Böhme (2002).

Figures

FIG. 2. — aff. Palaeocordylus bohemicus Roček, 1984 from the locality Merkur-North; right dentary (Ah-1088 SGDB) in lingual view. Scale bar: 5 mm.

FIG. 3.— aff.Palaeocordylus bohemicus Roček,1984;detail of the region with intramandibular septum. Scale bar: 2 mm.

FIG. 4. — aff. Palaeocordylus bohemicus Roček, 1984; detail of the tooth from the medial region of the dentary tooth row in lingual view (terms after Richter 1994). Scale bar: 200 µm.

FIG. 5. — aff. Palaeocordylus bohemicus Roček, 1984; detail of the 6th-12th tooth in posterolingual view. Scale bar: 500 µm.