Natrix merkurensis, Ivanov, 2002

Ivanov, Martin, 2002, The oldest known Miocene snake fauna from Central Europe: Merkur-North locality, Czech Republic, Acta Palaeontologica Polonica 47 (3), pp. 513-534 : 525-527

Natrix merkurensis sp. nov.

Derivation ot the name: merkurensis ,fromMerkur(nameofthetypelocality).

Type locality: Merkur−North—opencast brown coal mine near Tušimice, Czech Republic.

Stratum typicum: Orleanian ( MN 3a). Early Miocene.

Holotype: Fragmentary right compound bone ( SGDB Ah−315).

Paratype: 1 left ectopterygoid ( SGDB Ah−313), 1 anterior precaudal vertebra ( SGDB 7408 /MI−62) .

Remaining material.—Two(left+right)quadrate(SGDBAh−312; SGDB Ah−624), 2 right maxillaries ( SGDB 7408/MI−102; SGDB Ah−314), 3 (1 left + 2 right) compound bones ( SGDB Ah−315–317), 213 precaudal vertebrae ( SGDB 7408/MI−63–83; SGDB 7408/MI−96–98; SGDB Ah−318–504; SGBD Ah−625), 8 caudal vertebrae ( SGDB Ah−505–511; SGDB Ah−626).

Diagnosis.—Alarge natricine snake assigned to the genus Natrix on the basis of: 1, the presence of a distinct crest on the dorsal surface of the external ramus; 2, the relatively low flanges of the mandibular fossa; 3, the supraangular foramen situated far from the rostral end of the mandibular fossa; 4, the morphology of vertebrae that are closely similar to the recent representatives of this genus. The compound bone most resembles that of the recent N. natrix but it differs by a more massive structure and the higher labial flange of the mandibular fossa. It differs from all recent and fossil ( N. longivertebrata , N. sansaniensis ) species in having very prominent crest on the inner side of the lingual flange of the mandibular fossa. The vertebrae are similar to those of N. longivertebrata and N. natrix but N. merkurensis sp. nov. differs from all recent and fossil members of the genus Natrix in having a much more higher neural spine (with exception of N. sansaniensis ). N. merkurensis sp. nov. differs from N. sansaniensis on the basis of: 1, the larger size; 2, the rounded distal tip of the hypapophysis; 3, the enlarged prezygapophyseal articular facets in precaudal vertebrae.

Description of the holotype

Right compound bone ( Fig. 8D 1 , D 2 ).—The rostral part is broken off. The labial flange of the mandibular fossa is comparatively low and the border of this flange is concave in the proximity of the facet for articulation with the quadrate. The supraangular crest is distinct and long. The lingual flange is about 1.5 times higher than the labial one. The retroarticular process is strong and its pointed distal end is curved medially. The supraangular foramen occurs far from the rostral termination of the mandibular fossa. In lingual view, a very distinct and prominent crest occurs on the lingual flange; this crest extends from the ventral margin of the retroarticular process to the proximity of the antero−dorsal termination of the lingual flange.

Description of paratypes

Ectopterygoid ( Fig. 8A ).—The bone is fragmentary and its caudal part is lacking. The external ramus of the maxillary articulation is convex and rectangular. Adistinct crest is devel − oped on the dorsal surface of the external ramus and this crest turnsandextendsalongtheoutersideofthebonebody.Theinternalramusformsaboutarightanglewiththeexternalramus.

Anteriorprecaudalvertebra ( Fig. 9A 1 –A 5 ).—The vertebra is fragmentary with broken off hypapophysis, the right prezygapophyseal process, and the right parapophyseal process. In lateral view, the neural spine is almost as long as high. Its cranial margin overhangs anteriorly and the caudal margin overhangs posteriorly. Interzygapophyseal ridges are distinct. The distinct lateral foramina occur in shallow depressions. The subcentral ridges are prominent and are arched dorsally. The parapophyses and diapophyses are distinctly separated from each other and the diapophyses are about as large as the parapophyses. The diapophyses are directed laterally in dorsal view. The left parapophyseal process is directed anteriorly. The distinct and deep hypapophysis is broken off near its base. In dorsal view, the cranial margin of the crenate zygosphene has expanded median lobe. The left prezygapophyseal articular facet is widely oval, the right facet is partially fragmentary. The antero−laterally directed left prezygapophyseal process is longer than the prezygapophyseal facet. The epizygapophyseal spines are prominent. In ventral view, the subcentral grooves are shallow. The subcentral foramina are minute. The anterior keel of the hypapophysis is triangularly expanded and the very distinct subcotylar tubercles are developed at the ventral side of the cotylar rim. The postzygapophyseal articular facets are irregularly shaped. In cranial view, the neural arch is moderately vaulted and the neural canal is rounded and the zygosphene is straight. The small paracotylar foramina lie in depressions on either side of the rounded cotyle.

Description of the remaining material

Quadrate ( Fig. 8B ).—In postero−lateral view, the bone is wide and flat. The bone body is wide in the proximity of the trochlea quadrati and it expands towards the dorsal crest. The dorsal crest is thin and lacks dorso−ventral widening. The quadrate crest is prominent especially in the middle of the bone length. The stapedial process is distinct but it is not well demarcated from the bone.

Maxillary ( Fig.8C ).—Inthemorecompletebone,therostral part, including the prefrontal process is broken off. The ectopterygoid process is distinct, as long as wide, is directed medially and its medial part is curved ventrally. The teeth are not preserved; 9 tooth sockets occur on the fragmentary row. The last 2–3 tooth sockets are markedly larger and a gap in the tooth row is lacking.

Compound bone.—The bones are fragmentary and their rostral and caudal terminations are broken off. They do not differ from the holotype.

Precaudalvertebrae ( Fig. 9B 1 –B 5 ).—It is difficult to distinguish between cervical and trunk vertebrae in the subfamily Natricinae . Therefore, both are discussed under the heading of “precaudal vertebrae”. Precaudal vertebrae do not differ significantly from the paratype. The vertebrae from the anterior part of the column differ from the posterior precaudal vertebrae generally by the higher neural spine and the deeper hypapophysis. The dorsal margin of the neural spine is usually distinctly thickened and both its cranial and caudal extremities may be slightly bifurcate. However, most of neural spines and all hypapophyses are broken off. The zygosphene is straight to slightly convex in cranial view. In caudal view, the small (often paired) parazygantral foramina may be visible. Measurements are as follow (n = 25): cl: or = 5.05–6.86 mm; naw: or = 2.98–4.25 mm; cl/naw: or = 1.53–2.00, mean 1.67±0.11.

Caudal vertebrae ( Fig. 9C 1 –C 4 ).—All vertebrae are dam−

B 2 B3 C3

Figures

Fig. 8. Natrix merkuriensis sp. nov. from the Early Miocene (MN 3a) of Merkur−North.A. Left ectopterygoid (SGDB Ah−313, paratype). B. Right quadrate (SGDB Ah−312). C. Right maxillary (SGDB Ah−314). D1, D2. Right compound bone (SGDB Ah−315, holotype). In dorsal (A), postero−lateral (B), ventral (C), labial (D1), and lingual (D2) views. Scale bar 2 mm.

Fig. 1. The distribution of some Early and Middle Miocene ophidian localities in the areas of Germany, Czech Republic, Slovak Republic, Poland and Austria. 1, Weisenau (MN 1); 2, Hessler (MN 1); 3, Ulm−Westtangente (MN 2); 4, Stubersheim 3 (MN 3); 5, Merkur−North (MN 3a); 6, Dolnice (MN 4); 7, Petersbuch 2 (MN 4); 8, Langenau (MN 4); 9, Oberdorf (MN 4); 10, Randecker Maar (MN 5); 11, Eichstätt (MN 4–6); 12, Ivančice (MN?4–6); 13, Oggenhausen (MN 5/6); 14, Przeworno (MN 5–6); 15, Devínska Nová Ves (MN 6); 16, Vösendorf; 17, Sandelzhausen (MN 6); 18, Rothenstein 13 (MN 6); 19, Opole (MN 7); 20, Öhningen (MN 7+8); 21, Steinheim am Albuch (MN 7+8).

Fig. 2. Bavarioboa sp. from the Early Miocene (MN 3a) of Merkur−North; A1–A4. Cervical vertebra (SGDB Ah−2). B1–B5. Mid−trunk vertebra (SGDB 7408/MI−1). In lateral (A1, B1), dorsal (A2, B2), ventral (A3, B3), cranial (A4, B4), and caudal (B5) views. Scale bar 2 mm.

Fig. 9. Natrix merkurensis sp. nov. from the Early Miocene (MN 3a) of Merkur−North. A1–A5. Anterior precaudal vertebra (SGDB 7408/MI−62, paratype). B1–B5. Mid−trunk vertebra (SGDB 7408/MI−75). C1–C4. Caudal vertebra (SGDB SGDB−Ah−505). In lateral(A1, B1, C1),dorsal(A2, B2, C2),ventral(A3, B3, C3), cranial (A4, B4, C4), and caudal (A5, B5) views. Scale bar 2 mm.

Fig. 5. Coluber caspioides Szyndlar and Schleich, 1993 from the Early Miocene (MN 3a) of Merkur−North. A1, A2. Left frontal (SGDB Ah−44). B. Right palatine (SGDB Ah−46). C1, C2. Right pterygoid (SGDB Ah−45). D. Right quadrate (SGDB Ah−l 1). E. Left dentary (SGDB Ah−48). F1, F2. Right compound bone (SGDB Ah−49). G1–G5. Cervical vertebra (SGDB Ah−51). H1, H2. Mid−trunk vertebra (SGDB Ah−615). I1–I5. Posterior trunk vertebra (SGDB 7408/MI−37). In dorsal (A1, C1, G2, H2, I2), ventral (A2, B, C2, G3, I3), postero−lateral (D), labial (E, F1), lingual (F2), lateral (G1, H1, I1), cranial (G4, I4), and caudal (G5, I5) views. Scale bar 2 mm.

Fig. 4. Coluber suevicus (Fraas, 1870) from the Early Miocene (MN 3a) of Merkur−North. A. Right quadrate (SGDB−Ah−33). B1–B3. Cervical vertebra (SGDB−Ah−36). C1–C5. Trunk vertebra (SGDB 7408/MI−26). In postero−lateral (A), lateral (B1, C1), dorsal (B2, C2), ventral (B3, C3), cranial (C4), and caudal (C5) views. Scale bar 2 mm.