COLUBRINAE, Oppel, 1811

Ivanov, Martin, Čerňanský, Andrej, Bonilla-Salomón, Isaac & Luján, Àngel Hernández, 2020, Early Miocene squamate assemblage from the Mokrá-Western Quarry (Czech Republic) and its palaeobiogeographical and palaeoenvironmental implications, Geodiversitas 42 (20), pp. 343-376 : 360-362

“ COLUBRINAE ” indet., type 1

( Fig. 10 )

Coluber sp. 2 – Ivanov & Musil 2004: 229 (in part).

Coluber sp., type II – Ivanov et al. 2006: 229, table 2 (in part).

MATERIAL. — MWQ, early Miocene, Burdigalian, Orleanian, MN 4: 1/2001 Turtle Joint: 15 trunk vertebrae (Pal. 1464- 1478), 2 caudal vertebrae (Pal. 1479, 1480); 2/2003 Reptile Joint: Six trunk vertebrae (Pal. 1960-1965), 2 caudal vertebrae (Pal. 1966, 1967).

DESCRIPTION

Trunk vertebrae

Preserved fragmentary vertebrae ( Fig. 10 A-L) are rather small with a maximum length of 4.16 mm for the largest vertebra and a width of 2.55 mm. In lateral view, the cranial

margin of the neural spine is inclined anteriorly whereas caudal margin is inclined posteriorly. The neural spine is about twice to three times longer than high ( Fig. 10A, F ).

The interzygapophyseal ridges are absent or indistinctly developed. The lateral foramina sit in shallow depressions. The paradiapophyses are markedly small with parapophysis

somewhat smaller than the diapophysis. The subcentral ridges are almost straight but on the anteriormost trunk vertebrae they are dorsally slightly arched ( Fig. 10A ). In dorsal view, the zygosphene is wide with small and pointed lateral lobes and a rather wide and blunt medial lobe; thus, the cranial margin of the zygosphene appears to be convex. The prezygapophyseal articular facets are rather small with an oval outline and their long axis extended anterolaterally. The only preserved right prezygapophyseal process is slen- der and almost as long as the prezygapophyseal facet. It is anterolaterally directed with a pointed distal termination. In ventral view, the vertebral centrum is elongated craniocaudally. The morphology of the haemal keel strongly depends on its position within the vertebral column. On anterior trunk vertebrae, the haemal keel is narrow and sometimes has a sharp ventral margin. In the middle trunk vertebrae, the haemal keel extends slightly towards the caudal margin of the centrum, and rather indistinct furrows sometimes occur along the haemal keel’s axis. In the posterior trunk vertebrae, the ventral margin of the haemal keel is rather flat and may laterally overhang its narrow base slightly ( Fig. 10K, L ). The subcotylar tubercles are absent, the subcentral grooves are shallow, and the subcentral foramina are very small. The subcentral ridges are usually rather blunt. The parapophyses are rather short. The postzygapophyseal articular facets are subrectangular and slightly laterally elongated. In cranial view, the neural arch is vaulted, and the neural canal is wide and rounded with small lateral sinuses. The cranial margin of the zygosphenal lip is arched dorsally but the medial lobe can be bent slightly ventrally. The prezygapophyseal processes are also bent slightly ventrally. The paracotylar foramina occur within deep depressions on either side of the slightly dorsoventrally depressed cotyle. In caudal view, the zygantral area is wide. The base of the condyle is flattened. The vertebral dimensions of the largest vertebrae from 1/2001 Turtle Joint are as follows (n = 7): cl: or = 3.65-4.16 mm; naw: or = 2.19-2.55 mm; cl/naw: or = 1.56-1.71, mean 1.65 ± 0.05.

Caudal vertebrae

The more complete vertebra ( Fig. 10 M-P) is fragmentary with loss of the distal tips of the pleurapophyses and haemapophyses as well as damaged prezygapophyses. In lateral view, the neural spine height is about a quarter of its length. In dorsal view, the vertebra is strongly elongated craniocaudally. The neural arch is cylindrical. Prezygypophyses with strongly elongated prezygapophyseal articular facets are directed anteriorly rather than anterolaterally. Therefore, we conclude that these caudal vertebrae belong to the same taxon as above described trunk vertebrae.

REMARKS

The trunk vertebrae of this tiny snake are characterized by: 1) small dimensions; 2) interzygapophyseal ridges absent or moderately developed; 3) medial lobe of the zygosphene sometimes bent ventrally; 4) slender anterolaterally directed prezygapophyseal processes with pointed

distal terminations; 5) markedly small paradiapophyses with a short parapophysis that is somewhat smaller than the diapophysis; and 6) the rather blunt subcentral ridges. The vertebrae differ from those of extinct Eurasian small “colubrine” genera including Oligocene (MP 22, MP 30) and early to late Miocene (MN 4-MN 9) Texasophis ( Rage & Holman 1984; Augé & Rage 2000; Szyndlar 1987, 1991 a, 1994; Ivanov & Böhme 2011; Ivanov et al. 2019), late Miocene (MN 13) Hispanophis ( Szyndlar 1985) , middle Miocene (MN 6, MN 7+8) Paleohetorodon ( Rage & Holman 1984; Holman 2000), and two new genera of late Miocene or early Pliocene (MN 13/MN 14) colubrid snakes ( Georgalis et al. 2019) by the presence of blunt subcentral ridges and markedly small paradiapophyses. Such small paradiapophyses with rather short parapophyses do not occur in any known Eurasian fossil “colubrines” nor in studied extant representatives. Although similarly small paradiapophyses as well as blunt subcentral ridges occur in the Asiatic and North American genus Opheodrys Fitzinger, 1843 , the epizygapophyseal spines are underdeveloped, the prezygapophyseal articular facets are widely oval to almost circular in outline, and the prezygapophyseal processes are much shorter in this extant genus ( Parmley 1990; Holman 2000). Although “ Colubrinae ” indet., type 1 possibly represents a new taxon, the vertebral morphology of most Asiatic small “colubrines” is unknown and a more precise comparison will be necessary.

Figures

FIG. 10. — “Colubrinae” indet., type 1 from the early Miocene (MN 4) of MWQ. Middle trunk vertebra Pal. 1464 (1/2001 Turtle Joint) in right lateral (A), dorsal (B), ventral (C), cranial (D) and caudal (E) views. Middle trunk vertebra Pal. 1465 (1/2001 Turtle Joint) in right lateral (F), dorsal (G), ventral (H), cranial (I) and caudal (J) views. Posterior trunk vertebra Pal. 1466 (1/2001 Turtle Joint) in left lateral (K) and ventral (L) views. Caudal vertebra Pal. 1966 (2/2003 Reptile Joint) in right lateral (M), dorsal (N), ventral (O) and cranial (P) views. Abbreviations: cd, condyle; ct, cotyle; d, diapophysis; es, epizypapophyseal spine; hae, haemapophysis; hk, haemal keel; lf, lateral foramen; na, neural arch; nc, neural canal; ns, neural spine; p, parapophysis; pctf, paracotylar foramen; pl, pleurapophysis; pof, postzygapophyseal articular facet; prf, prezygapophyseal articular facet; prp, prezygapophyseal process; scf, subcentral foramen; scg, subcentral groove; scr, subcentral ridge; zy, zygosphene; zyg, zygantrum. Scale bar: 2 mm.