Colombophis portai Hoffstetter and Rage, 1977

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 : 366-371

Colombophis portai Hoffstetter and Rage, 1977

Figs. 2–5 ; Table 1.

1977 Colombophis portai Hoffstetter and Rage, 1977: 174–179 , fig. 4. 1997 Colombophis portai ; Hecht and LaDuke 1997: 95–96.

Holotype: MNHN. VIV 6, one midtrunk vertebra.

Type locality: Los Mangos, near La Venta, Departamento de Huila, Colombia; Fish Bed, Villavieja Formation, middle Miocene.

Emended diagnosis.— Colombophis portai differs from C. spinosus sp. nov. by its midtrunk vertebrae longer than broad, with a very low neural spine, resembling a tubercle and circular in outline in dorsal view; thin to moderate zygosphene; anterolaterally orientated prezygapophyses; and undivided paradiapophyses.

Referred material.—Four anterior trunk vertebrae, UFAC−PV 5715, IGM 184285 (1 and 3), and 184476 (2); eighteen midtrunk vertebrae, UFAC−PV 3478, 3480, 3484, 4089, 5716B; IGM 183533 (1), 183561 (1 to 2), 183928, 184086, 184131 (1 to 2), 184159 (1–3), 184285 (2), 184476 (1), 184579 (1 to 2), 184788, 184806, and 250914; and two posterior trunk vertebrae, UFAC−PV 2957 and IGM 183533(2).

Description.—Most of the vertebrae are fragmented and consist of isolated neural arches, centra, and other very incom−

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plete remains; nonetheless, they present the general features described by Hoffstetter and Rage (1977) for this species. In general, the vertebrae are medium to large size, in this respect approximating an extant boa of 177 cm (Boa constrictor, MCN.D. 333) for the holotype of Colombophis portai . Also , the vertebrae are robust and not strongly depressed, although longer and broader than high (pr−po> h, pr−pr> h). The anterior and posterior trunk vertebrae are smaller than the midtrunk vertebrae, but there is also variation in the size of the midtrunk vertebrae among the specimens from Colombia .

The neural arch is longer than broad (pr−po> pr−pr) and its roof is depressed, especially in the posterior vertebrae ( Fig. 4 ), whereas there is a slightly vaulted neural arch in the anterior trunk vertebrae ( Fig. 2 ). The posterodorsal notch of the neural arch is well defined but not very deep; each half of the roof being notably flattened. In lateral view, the neural arch rises posteriorly from about the origin of the anterior border of neural spine, which is restricted to the posterodorsal end of the neural arch, so far from the zygosphene. The roof of the neural arch between the anterior edge of the zygosphene and the anterior edge of neural spine is slightly concave. The neural spine is very low but relatively robust, similar to an almost imperceptible tubercle, circular in outline. The zygosphene is thin to moderate, but broader than the cotyle (zw> ctw). The anterodorsal edge of the zygosphene is variable between specimens, probably due to intraspecific variation. It can be rectilinear, notched or even slightly convex in dorsal view. The zygantra are small and deep, with a small foramen inside each zygantrum. The roof of the zygantra is almost rectilinear and continuous. The neural canal is large, high, and triangular in outline. The medial borders of the prezygapophyses lie at a high position, at the level of the middle of the neural canal. They are anterolaterally directed and strongly inclined dorsally from the horizontal plane. The prezygapophyseal facet is oval and large (prl> prw). The prezygapophyseal process is short, although, in dorsal view, it can be seen exceeding laterally the tip of the prezygapophyseal facet due to the strong inclination of the prezygapophyses. The postzygapophyses are also well inclined dorsally and posterolaterally orientated. The doi:10.4202/app.2009.1111

interzygapophyseal constriction, between pre− and postzygapophyses, is deep and anteroposteriorly short. The centrum is longer than the width of the neural arch (cl/naw> 1). It is smooth, not markedly widened anteriorly and rather narrow. The subcentral ridges are not developed or only weakly defined. The anterior trunk vertebrae bear a prominent hypapophysis on the posterior surface of the centrum, broken in all specimens ( Fig. 2 ). In the midtrunk vertebrae, there is a weakly developed haemal keel, which is anteriorly broad, smooth or convex, and usually narrower and prominent in the most posterior portion of the centrum ( Fig. 3 ). The posterior trunk vertebrae have a well developed haemal keel that is defined by the subcentral grooves ( Fig. 4 ). The subcentral grooves are shallow in the anterior, mid−, and posterior trunk vertebrae, from the ventral margin of the cotyle to the middle of the centrum. They delimit the haemal keel anterolaterally, and they narrow toward the precondylar constriction. The subcentral foramina are variably enlarged, reduced, or absent, and when present, located anterior to the prominent part of the haemal keel, and close to the sagittal plane of the centrum. They are usually located on the broad and flat anterior portion of the haemal keel ( Fig. 5 ). Most specimens have a haemal keel with a rounded distal end, slightly projecting below the ventral surface of the centrum. In some specimens (mainly observed in the midtrunk vertebrae), the haemal keel has a bilobed distal end, where there are two small and divergent apophyses more or less differentiated ( Fig. 5 ). The subcentral ridges and grooves are also morphologically distinct among specimens. The vertebrae that show bilobed haemal keel usually have relatively deep subcentral grooves. Despite the poor preservation of the vertebrae, we infer that these different morphologies are probably linked to regionalization of the column. The cotyle and condyle are almost circular, slightly broader than high. The cotyle is not or scarcely visible in ventral view because it is not inclined and its rim is continuous and prominent. The main axis of the condyle is not notably inclined above the horizontal plane. Only two specimens ( UFAC−PV 3484 and 3478) could represent juveniles, due to the small size, and because the cotyle and condyle are very dorsoventrally depressed. The presence of paracotylar foramina is irregular, indicating probably an intraspecific variation. Some specimens have only one foramen or a pair of foramina on each side of the cotyle ( UFAC−PV 4089, Fig. 3C ), but others do not show any foramina. In most specimens, the paradiapophyses are not preserved; when present they are relatively small, usually surpassing the ventral margin of the cotyle, and separated from it by well defined notches that become deeper in the posterior trunk vertebrae. The paradiapophyses are undivided. In the anterior and posterior trunk vertebrae, the paradiapophyses are almost vertical in lateral view, and in the midtrunk vertebrae they are posteroventrally inclined. In the posterior trunk vertebrae, the paradiapophyses are more prominent lateroventrally, although they maintain far from the level of the prezygapophyseal tip ( Fig. 4 ).

Stratigraphic and geographic range.— The material at UFAC−PV was recovered from Talismã ( Purus River , Amazonas State) and Patos (Acre River, Acre State) localities, Solimões Formation, late Miocene, Brazil ; and the material of the IGM belongs to the La Venta Fauna, La Victoria and Villavieja formations ( Fish and Monkey Beds), Honda Group, middle Miocene, Colombia .

Figures

Fig. 2. Alethinophidian snake Colombophis portai Hoffstetter and Rage, 1977, anterior trunk vertebrae from the La Victoria and Villavieja formations (middle Miocene, Colombia)–Solimões Formation (late Miocene, Brazil). A, B. IGM 184285(1). C, D. UFAC−PV 5715. Photographs (A, C) and schematic drawings (B, D), in anterior (A1–D1), posterior (A2–D2), lateral (A3–D3), dorsal (A4–D4), and ventral (A5–D5) views.

Fig. 3. Alethinophidian snake Colombophis portai Hoffstetter and Rage, 1977, midtrunk vertebrae from the La Victoria and Villavieja formations (middle Miocene, Colombia)–Solimões Formation (late Miocene, Brazil). A, B. IGM 183561. C, D. IGM 183928. E, F. UFAC−PV 4089. Photographs (A, C, E) and schematic drawings (B, D, F), in anterior (A1–F1), posterior (A2–D2), lateral (A3–D3, E2, F2), dorsal (A4–D4, E2, F2), and ventral (A5–D5, E4, F4) views.

Fig. 4. Alethinophidian snake Colombophis portai Hoffstetter and Rage, 1977, posterior trunk vertebra from the Solimões Formation (late Miocene, Brazil), UFAC−PV 2957. Photographs (A1–E1) and schematic drawings (A2–E2), in anterior (A), posterior (B), lateral (C), dorsal (D), and ventral (E) views.

Fig. 5. Colombophis portai Hoffstetter and Rage, 1977, schematic drawings of variations in the haemal keel from three incomplete midtrunk vertebrae (IGM 184159) from the La Victoria and Villavieja formations (Fish and Monkey beds) in ventral view. A. IGM 184159−1. B. IGM 184159−2.C. IGM 184159−3.