Colombophis sp.

Alfonso-Rojas, Andrés, Vanegas, Rubén D., Mariño-Morejón, Elizabeth & Cadena, Edwin-Alberto, 2023, Newly discovered fossils provide novel insights on the biology of the South American Miocene snake Colombophis Hoffstetter & Rage, 1977, Geodiversitas 45 (13), pp. 377-399 : 382-385

Colombophis sp.

REFERRED MATERIAL. — More than 20 vertebral fragments (see Appendix 3), most of them correspond to partially complete or fragmentary precloacal vertebrae.

REMARKS

Listed specimens were assigned to Colombophis as they exhibit the following features: medium to large size (cl = c. 8 mm, po-po = c. 11 mm); slightly depressed neural arch with a shallow median notch on the posterior border; the neural spine is reduced and restricted to the posterior end of the neural arch; moderately inclined prezygapophyses which usually reach the zygosphene roof level; short prezygapophyseal process; paracotilar foramina present in most vertebrae; weakly divided synapophyses; broad haemal keel with small to absent subcentral foramina close to the sagittal plane and bear one or two small apophyses with a tubercular shape placed on the ventral margin on anteriorly to the condyle. Lateral foramina located near the base of the neural canal anteriorly to the neural arch constriction.

DESCRIPTIONS

Anterior-trunk vertebrae

These vertebrae are shorter (cl <h) than the pre-cloacal vertebrae for Colombophis spp. ( C. portai , C. spinosus , and C. sp.). Despite being broken on most of the specimens, the hypapophyses are postero-ventrally oriented and located behind the sub-central foramina also, hypapophyses have a circular ( Fig. 3D ) or a flattened shovel-like shape ( Figs 3E ; 6E ) in posterior view.

Mid-trunk vertebrae

These vertebrae are the largest and most distinctive of Colombophis spp. Prezygapophyses are anterolaterally oriented, and usually reach the zygosphene roof level. Ventrally, the haemal keel is broad, usually with a pair of small sub-central foramina placed anterior to the coronal plane ( Figs 3A, B ; 4A, B ; 5I, J ; 6 A-C). The posterior end of the haemal keel usually presents a tubercular or bifid structure. Neural arch is broad and slightly depressed, visible from posterior region view. The zygantra possesses a deep foramen inside. Neural spines are restricted to the posterior region of the neural arch, being poorly developed (tubercle like) in C. portai ( Figs 3A, B ; 4 A-D; 5G, H), but well developed in C. spinosus where the anterior edge of this structure rarely reach the coronal plane of the vertebra ( Fig. 6 A-D).

Posterior-trunk vertebrae

These vertebrae are easily recognized by the presence of subcentral paramedian lymphatic fossae, which create a notched

A1 A2 A3 A4 A5

section between the cotyle and the synapophyses ( Figs 3F ; 4E, F ; 6F ). Pre-condylar constriction of the centrum is strong compared to anterior or mid-trunk vertebrae, which also makes the haemal keel less broad. Prezigapophyses are less inclined and do not reach the zygosphene level. In some specimens of C. portai , the posterior end of the haemal keel extends ventrally creating a structure similar to a hypapophysis ( Fig. 4E,F )

Ribs

Ribs are only present in VPPLT-1564 specimen, unfortunately they are badly preserved. However, they seem to be fully ossified and slender, apparently longer than the vertebral centrum ( Fig. 5C, D ). The articular facet is smooth without a clear division on the articular facets, which corresponds to undivided synapophyses.

A1 A2 A3 A4 A5

Post-cloacal vertebrae

A potential post-cloacal vertebra was found associated in the C. portai specimen VPPLT-1740.( Fig.7A ) This vertebra is considerably more vaulted than the associated precloacal vertebrae( Fig.4 ). Posteroventral blade like structures are present,resembling paired haemapophyses. The subcentral foramina faces antero-ventrally near to the base of haemapophyses. Prezygapophyses are short and more laterally oriented, with little or no inclination. The neural spine is a relatively high lamina, considerably different from the neural spine shape of Colombophis spp.

Ontogenetic variation

Most of the specimens belong to adults as they are fully ossified and present a medium to large size. However, VPPLT-1006

specimen ( Fig. 3A, B ), may represent a juvenile or sub adult individual based on its small size and the ovoid shape of the cotyle ( Hsiou et al. 2010), it also lacks a developed prezygapophyseal processes, it has a narrow zygosphene and a relatively large neural canal as it happens in extant and ancient snake neonates ( LaDuke 1991; Xing et al. 2018).

Parazygantral foramina

Parazygantral foramina are present in both species of Colombophis , but only in two specimens (VPPLT-1728 and VPPLT-1740), as well as in the holotype MNHN-VIV-6 ( Figs 4A, B ; 6A, B ; 7 ). These structures appear as a single foramen with or without small pits aside, which are interconnected internally with the foramen, ( Fig. 8 ). Pits may appear also in specimens

with no clearly defined foramen ( Figs 6C ; 8E, F ). The internal structure of the vertebrae reveals that the dorso-posterior region of the vertebra (postzygapophyses and neural arch) is highly vascularized, where the parazygantral foramina and its associated pits are interconnected with the zygantral and lateral foramina. This feature is particularly visible in VPPLT-1728 specimen, where the internal structure is infilled with a denser material that creates a perfect endocast of the vertebra ( Fig. 8G, H ).

Figures

FIG. 3. — Colombophis portai Hoffstetter & Rage, 1977 specimens! A, B, VPPLT-1006; C, VPPLT-0067; D, VPPLT-0068; E, VPPLT-1739; F, VPPLT-1735. Views: 1, anterior;2, dorsal; 3, lateral;4, ventral, 5, posterior views. Scale bars: 10 mm.

FIG. 6. — Colombophis spinosus Hsiou, Albino & Ferigolo, 2010 from the Tatacoa Desert: A, B, VPPLT-1728; C, VPPLT-0798; D, VPPLT-1093; E, VPPLT-1741; F, VPPLT-1534. Views: 1, anterior; 2, dorsal; 3, lateral; 4, ventral, 5, posterior views. Scale bars: 10 mm.

FIG. 4. — Colombophis portai Hoffstetter & Rage,1977 VPPLT-1740 specimen,which consists of seven associated vertebrae:A, B, mid-trunk vertebra;C, D, midtrunk vertebra; E, F, posterior-trunk vertebra. Views: 1, anterior; 2, dorsal; 3, lateral; 4, ventral; 5, posterior views. Scale bar: 10 mm.

FIG. 5. — Colombophis portai Hoffstetter & Rage, 1977 VPPLT-1564 specimen: A, B, nine articulated precloacal vertebrae; C, D, several fragments of precloacal vertebrae and ribs embedded in the rock matrix; E-I, three articulated precloacal vertebrae in dorsal (E, F), anterior (G) and ventral (H, I) views; J-M, isolated vertebra in anterior (J, K) and posterior (L, M) views. Scale bars: A, B, 50 mm; C-N, 10 mm.

FIG. 7. — Comparison of VPPLT-1740 post cloacal vertebrae with extant aletinophidians:A, VPPLT-1740 specimen;B, Boa cf.constrictor Linnaeus,1758,VPPLTuncatalogued specimen;C, Tropidophis melanurus (Schlegel,1837),UF-H-52001; D, Anilius scytaleLinnaeus,1758,UF-H-52001; E, Cylindrophis ruffusLaurenti, 1768, UF-H-52673. Views: 1, anterior; 2, dorsal; 3, lateral; 4, ventral, 5, posterior views. Scale bars: A, B, 10 mm; C, 5 mm; D, E, 3 mm.

FIG. 8. — Parazygantral foramina in Colombophis spp. vertebrae: A, B, C. portai Hoffstetter & Rage, 1977, MNHN VIV-6 (see also Appendix 7); C, D, C. portai, VPPLT-1740; E, F, C. spinosus Hsiou, Albino & Ferigolo, 2010, VPPLT-798; G, C. spinosus, VPPLT-1728; H, endocast of VPPLT-1728 showing the internal vascularization of the vertebra. Colors: blue, parazygantral foramina; green, zygantral foramina; red, lateral foramina. Views: 1, dorsal; 2, lateral; 3, posterior. Scale bars: A-F, 5 mm; G, H, 10 mm.