Colombophis spinosus, Hsiou & Albino & Ferigolo, 2010

Hsiou, Annie S., Albino, Adriana M. & Ferigolo, Jorge, 2010, Reappraisal of the south American Miocene snakes of the genus Colombophis, with description of a new species, Acta Palaeontologica Polonica 55 (3), pp. 365-379 : 371-375

Colombophis spinosus sp. nov.

Figs. 6–8 , Tables 1, 2.

2006 Colombophis cf. C. portai ; Head et al. 2006: 234–236, fig. 1A.

Etymology: From the Latin spinosus , meaning spined, a reference to the high neural spine.

Holotype: UFAC−PV 2953 , one almost complete midtrunk vertebra.

Type locality: Talismã locality, Purus River, Amazonas State, Brazil. Type horizon: Late Miocene, Solimões Formation .

Diagnosis.— Colombophis spinosus differs from C. portai in having shorter than broad vertebrae; robust and high neural spine, with a vertical main axis, and cylindrical in dorsal view; moderately thick zygosphene; prezygapophyses well laterally oriented; and weakly divided paradiapophyses.

doi:10.4202/app.2009.1111

Referred material.—Two incomplete anterior trunk vertebrae, UFAC−PV 1609 and 2952; eight incomplete midtrunk vertebrae, AMU−CURS 154, IGM 184176(1), UFAC−PV

2955, 2956, 4027, 5424, 5716C, and 5716E; and one incomplete posterior trunk vertebra, UFAC−PV 3485.

Description.—Although some vertebrae are somewhat fragmented, data association, comparisons and description were possible, mainly based on the holotype. There are variations in vertebral morphology, but in general, the vertebrae are large, robust and high; higher than long (h> pr−po) and broader than high (pr−pr> h), with a centrum that is shorter than the width of the neural arch (cl/naw<1), and a neural arch much shorter than broad (pr−po <pr−pr).

In anterior view, the neural arch is broad due to the long prezygapophyses. The zygosphene is rather thick and shows a straight dorsal margin, having small zygosphenal articular facets that are inclined dorsally. In two anterior trunk vertebrae ( UFAC−PV 1609 and 2952), the dorsal margin of the zygosphene is slightly elevated in the middle. The width of the zygosphene varies considerably relative to the transverse diameter of the cotyle, being nearly equal as in the holotype (zw~ctw), wider, or even narrower than the cotyle. The prezygapophyses are slender, long and strongly inclined dorsolaterally, around 25° from the horizontal plane, reaching the level of the dorsal margin of the zygosphene ( Figs. 6 and 7 ). The prezygapophyseal process is small and robust. The neural canal is small and high, trapezoidal in the holotype but triangular in most specimens. The cotyle is nearly circular (ctw~cth). One pair of paracotylar foramina is observed in all specimens (one foramen on each side of the cotyle), except in AMU−CURS 154 , which does not have any doi:10.4202/app.2009.1111

foramen, considered consistent with intraspecific variation as in C. portai . The paradiapophyses, fragmented on the left side in the holotype, are relatively small, not surpassing the ventral margin of the cotyle. In the posterior trunk vertebra ( UFAC−PV 3485 ), the paradiapophyses extend further laterally, almost reaching the median level of the prezygapophyses, the parapophyseal facet almost exceeding the ventral limit of the cotyle, probably due to the greater lateral expansion and the anteroventral orientation of the parapophyseal facet ( Fig. 8 ) .

In posterior view, the two halves of the neural arch are considerably flattened. The neural spine is robust and cylindrical, remarkably high and columnar. The posterodorsal notch of the neural arch is relatively well marked. The neural arch is more depressed in the posterior trunk vertebra (UFAC−PV 3485). The postzygapophyses are elongated and strongly inclined dorsolaterally. The zygantra are large and deep, with a small foramen inside. The articular surfaces are well developed, and the roof of each zygantrum constitutes a continuous and straight dorsal margin in the holotype. The condyle is nearly circular. Ventral to the condyle, the haemal keel can be seen sometimes as a posterior prominence (mid− and posterior trunk vertebrae), or as a well developed hypapophysis in the anterior trunk vertebrae.

In lateral view, the neural spine is robust and well developed, being considerably higher in some specimens ( UFAC−PV 1609 , 2952 , 2956 , 4027 , and 5716E), and has an epiphyseal articular facet in the distal end. It is very short anteroposteriorly and its anterior margin is slightly concave, distant from the zygosphene. It is restricted to the posterior extremity of the neural arch, and is vertical in orientation. On the posterolateral margin of the neural spine, a crest follows up on each side, as the continuation of the posterior margin of the neural arch. The side walls of the neural arch are short. The paradiapophyses are robust and are located ventrally far from the prezygapophyseal articular surfaces. The dia− and parapophysial surfaces are weakly separated; the diapophysis is slightly convex and the parapophysis is rather concave. The cotyle is strongly prominent in some specimens, where the anterolateral edge surpasses the level of the anterior edge of the zygosphene. Small lateral foramina are visible on the lateral walls of the neural arch, more or less positioned at the diapophysial level (holotype) or just above it (other specimens). The length of the centrum is smaller than the width of the neural arch (cl/naw <1), and clearly inclined posteroventrally in the holotype and other specimens, where it distally bears a relatively prominent haemal keel that is limited laterally by relatively well marked and deep subcentral grooves .

In dorsal view, the neural arch is much shorter than broad (pr−po <pr−pr). The posterodorsal notch of the neural arch is well−marked but not deep, and the broad and robust base of the neural spine grows up in its midline. The surface between the anterior edge of zygosphene and the neural spine is horizontally oriented and smooth, where the distance between the two structures is relatively large, due to fact that the neural spine is situated well posteriorly. The articular facets of the prezygapophyses are comparatively slender, longer than broad (prl> prw), and the main axis is strongly laterally orientated. A small and sharp−edged prezygapophyseal process projects beyond the articular facet of the prezygapophysis. In the posterior trunk vertebra, the prezygapophyses are anterolaterally directed. The postzygapophyses are strongly oriented laterally. The interzygapophyseal constriction is well−marked and very short, between the pre− and postzygapophysis on each side. The anterior margin of the zygosphene is straight or concave.

In ventral view, the centrum is triangular, its ventral face being broadly rounded anteriorly, very short (cl <naw), and wide. In the holotype, UFAC−PV 3485 , 4027 , and 5716E (midtrunk vertebrae), the subcentral grooves are deep from the ventrolateral margin of cotyle until mid−length of the centrum, limiting anterolaterally the haemal keel, which narrows posteriorly. In the UFAC−PV 1609 , 2952 , and 2956 (anterior vertebrae), the subcentral grooves are limited and more evident in the middle portion of the centrum, and there is a hypapophysis in the most posterior portion. The haemal keel is conspicuous, although not very prominent in the midtrunk vertebrae. Usually, it has two divergent margins in its posterior rim that produce a bilobed aspect, attaining the precondylar constriction. Near mid−length of the centrum, on each side of the haemal keel, there are small subcentral foramina, anterolaterally situated and very close together. The subcentral ridges are relatively well marked, extending approximately from the level between the dia−and parapophyses to the condyle. In the holotype and in UFAC−PV 2952 , 3485 , 4027 , and 5716E, the paradiapophyses are separated from the ventrolateral edge of the cotyle by a small and shallow notch. In other specimens, this constriction is discreet and subtle, probably in part due to the high degree of fragmentation in this region. Much of the condylar surface is exposed in ventral view, where the precondylar constriction is moderately marked .

Remarks.—After comparison of Colombophis vertebrae, it became clear that some differences cannot be attributed to intraspecific or intracolumnar variation, and hence warrant the erection of a new species. These differences are mainly the proportions of the vertebrae, the height of the neural spine, the morphology of the paradiapophyses, and the robustness of the zygosphene. The neural arch and centrum of the midtrunk vertebrae of C. spinosus are shorter than in C. portai . This is a result of the zygapophyses being laterally oriented in C. spinosus , producing a short neural arch, and values of the centrum length much lower than the width of the neural arch in the middle (cl/naw <1). In contrast, the zygapophyses are more anterolaterally directed in C. portai and the centrum length is subequal to or greater than the width of the neural arch in the middle (cl/naw Ẑ 1). In addition, the paracotylar notches and subcentral grooves seem to be relatively more marked in C. spinosus than in C. portai . The neural spine is high, clearly distinctive, very robust, with the main axis vertical in C. spinosus , but it is very low and reduced to a small tubercle in C. portai . The dia− and parapophyseal articular surfaces are weakly distinguishable in C. spinosus , but they are undistinguishable in C. portai . Furthermore, the zygosphene of C. portai is thin to moderate, whereas it is usually thicker in C. spinosus . Based on these characters, it is possible to support the recognition of two species of Colombophis .

Recently, Head et al. (2006: fig. 1A) assigned one precloacal vertebra from the middle Miocene of Venezuela to Colombophis cf. C. portai (AMU−CURS 154). According to the authors, the specimen is morphologically indistinguishable from the specimens of C. portai from the middle Miocene of the La Venta Fauna. Nevertheless, the description of this specimen and the direct observation of its features are consistent with the vertebral morphology of C. spinosus . According to the description of Head et al. (2006), this specimen shows no paracotylar foramina (congruent with the intracolumnar variation of Colombophis ) and has paradiapophyses strongly divided. The latter is a character that contrasts with the diagnosis of the genus, but according to our observations, AMU−CURS 154 displays paradiapophyses weakly divided into two articular facets, where the diapophysis is slightly convex and the parapophysis is rather concave, which support its reference to C. spinosus . In addition, this vertebra is evidently short (neural arch and centrum), the zygapophyses are laterally oriented and define a very short interzygapophyseal constriction, the neural spine looks higher than in C. portai , and the zygosphene is thick, all characters observed in C. spinosus .

Stratigraphic and geographic range.—Eight trunk vertebrae (UFAC−PV 1609, 2952, 2955, 2956, 3485 4027, 5716C, and 5716E) recovered from the Talismã locality, Purus River; one vertebra (UFAC−PV 5424) collected at the Morro do Careca locality. All of them come from the Solimões Formation, late Miocene, Amazonas State, Brazil. The vertebra IGM 184176 (1) belongs to the La Venta Fauna, La Victoria Formation (Duke University Locality 084), Honda Group, middle Miocene, Colombia. The material at the AMU−CURS is from the Upper Member of the Socorro Formation, middle Miocene of Venezuela.

Figures

Fig. 6. Alethinophidian snake Colombophis spinosus sp. nov., holotype, UFAC−PV 2359, midtrunk vertebra from the Solimões Formation (middle Miocene, Brazil). Photographs (A1–E1) and schematic drawings (A2–E2), in anterior (A), posterior (B), lateral (C), dorsal (D), and ventral (E) views.

Fig. 7. Alethinophidian snake Colombophis spinosus sp. nov., photographs of anterior and midtrunk vertebrae from the La Victoria and Villavieja formations (middle Miocene, Colombia)–Solimões Formation (late Miocene, Brazil), IGM 184176−1 (A), UFAC−PV 1609 (B), UFAC−PV 2952 (C), UFAC−PV 2956 (D), UFAC−PV 4027 (E), and UFAC−PV 5716E (F), in anterior (A1–F1), posterior (A2–F2), lateral (A3–F3), dorsal (A4–F4), and ventral (A5–F5) views.

Fig. 8. Alethinophidian snake Colombophis spinosus sp. nov., UFAC−PV 3485, photograph of posterior trunk vertebra, from the Solimões Formation (late Miocene, Brazil), in anterior (A), posterior (B), lateral (C), dorsal (D), and ventral (E) views.