Hsiou et al., 2010 - Colombophis

Hsiou et al., 2010 - Colombophis

(Parte 2 de 4)

200 km

Purus River

Rio Branco

500 km

Morro do Careca

Patos

Fig. 1. Location map of the fossiliferouslocalities of Colombophis in northern South America. A. La Victoria (1), Villavieja (2), and Urumaco (3). B. Morro do Careca (4), Talismã(5), and Patos (6).

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. 3) for the holotype of Colombophis portai.A lso, the vertebrae are robust and not strongly depressed, although longer and broader than high (pr−po > h, pr−pr > h). The ante− rior and posterior trunk vertebrae are smaller than the mid− trunk 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 postero− dorsal 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 out− line. The zygosphene is thin to moderate, but broader than the cotyle (zw > ctw). The anterodorsal edge of the zygo− sphene is variable between specimens, probably due to intra− specific 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 neu− ral 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 antero− laterally directed and strongly inclined dorsally from the horizontal plane. The prezygapophyseal facet is oval and large (prl > prw). The prezygapophyseal process is short, al− though, in dorsal view, it can be seen exceeding laterally the tip of the prezygapophyseal facet due to the strong inclina− tion of the prezygapophyses. The postzygapophyses are also well inclined dorsally and posterolaterally orientated. The

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Fig. 2. Alethinophidian snake Colombophis portai Hoffstetter and Rage, 1977, anterior trunk vertebrae from the La Victoria and Villavieja formations (middleMiocene, Colombia)–SolimõesFormation(lateMiocene, Brazil).A, B. IGM184285(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.

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HSIOU ET AL.—MIOCENE SNAKES FROM SOUTH AMERICA 369 5mm

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Fig. 3. Alethinophidian snake Colombophis portai Hoffstetter and Rage, 1977, midtrunk vertebrae from the La Victoria and Villavieja formations (middle Miocene,Colombia)–SolimõesFormation(lateMiocene,Brazil).A,B.IGM183561.C,D.IGM183928.E,F.UFAC−PV4089.Photographs(A,C,E)and

interzygapophyseal constriction, between pre− and postzyga− pophyses, 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 de− fined. The anterior trunk vertebrae bear a prominent hypa− pophysis 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 poste− rior trunk vertebrae have a well developed haemal keel that is

Table1.Vertebralmeasurementsofanterior,mid−,andposteriortrunk vertebraeofthespeciesofColombophis.Non−availabledataaremarkedwith a dash. Abbreviations: cl, centrum length; coh, condyle height; cow, condyle width; cth, cotyle height; ctw, cotyle width; h, total height of vertebra; naw, neural arch width at interzygapophyseal ridge; nch, neural canal height; ncw, neural canal width; nsh, neural spine height; po−po, width across postzygapophyses;pr−pr,widthacrossprezygapophyses;pr−po,distancebetweenpre−andpostzygapophysesofthesameside;prl,prezygapophysis length; prw, prezygapophysis width; zh, zygosphene height; zw, zygosphene width.

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 ab− sent, 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 ante− rior 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 diver− gent apophyses more or less differentiated (Fig. 5). The subcentral ridges and grooves are also morphologically dis− tinct 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 regio− nalization 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 rep− resent 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 fora− men or a pair of foramina on each side of the cotyle (UFAC−PV 4089, Fig. 3C), but others do not show any fo− ramina. In most specimens, the paradiapophyses are not pre− served; when present they are relatively small, usually sur− passing 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 verte− brae they are posteroventrally inclined. In the posterior trunk vertebrae, the paradiapophyses are more prominent latero− ventrally, 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, Ama− zonas 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 Villaviejaformations(FishandMonkeyBeds),HondaGroup, middle Miocene, Colombia.

Colombophis spinosussp. nov. Figs. 6–8, Tables 1, 2.

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

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

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

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HSIOU ET AL.—MIOCENE SNAKES FROM SOUTH AMERICA 371

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Fig. 5. Colombophisportai Hoffstetterand Rage, 1977, schematicdrawings of variations in the haemal keel from three incomplete midtrunk vertebrae (IGM 184159) from the La Victoria and Villavieja formations (Fish and Monkeybeds)inventralview.A.IGM184159−1.B.IGM184159−2.C.IGM 184159−3.

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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 schematicdrawings (A2–E2), in anterior(A), posterior(B), lateral(C), dorsal (D), and ventral (E) views.

Referred material.—Two incomplete anterior trunk verte− brae, 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 incom− plete posterior trunk vertebra, UFAC−PV 3485.

Description.—Although some vertebrae are somewhat frag− mented, 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 verte− brae (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, reach− ing the level of the dorsal margin of the zygosphene (Figs. 6

Table 2. Comparative measurements of Colombophis and of the fossil andlivingAnilioideaspecies.Non−availabledataaremarkedwithadash. Abbreviations:cl,centrumlength;h,totalheightofvertebra;pr−pr,width across prezygapophyses.

neural canal prezygapophysis paracotylar foramen cotyle paradiapophysis neural spine zygantrum condyle postzygapophysis neural spine lateralforamen diapophysis parapophysis subcentralforamen haemal keel zygosphene neural spine prezygapophyseal articular facetprezygapophyseal process interzygapophyseal constriction subcentral foramen subcentral ridge postzygapophyseal articular facet subcentral groove haemal keel

Fig. 6. Alethinophidian snake Colombophis spinosus sp. nov., holotype, UFAC−PV 2359, midtrunk vertebra from the Solimões Formation (middle and 7). The prezygapophyseal process is small and robust. The neural canal is small and high, trapezoidal in the holo− type but triangular in most specimens. The cotyle is nearly circular (ctw~cth). One pair of paracotylar foramina is ob− served in all specimens (one foramen on each side of the cotyle),except inAMU−CURS154, whichdoesnothave any doi:10.4202/app.2009.1

HSIOU ET AL.—MIOCENE SNAKES FROM SOUTH AMERICA 373

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Fig. 7. Alethinophidian snake Colombophis spinosus sp. nov., photographs of anterior and midtrunk vertebrae from the La Victoria and Villavieja forma− tions (middle Miocene, Colombia)–Solimões Formation (late Miocene, Brazil), IGM 184176−1 (A), UFAC−PV 1609 (B), UFAC−PV 2952 (C), UFAC−PV 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 later− ally, almost reaching the median level of the prezygapo− physes, the parapophyseal facet almost exceeding the ventral limit of the cotyle, probably due to the greater lateral expan− sion and the anteroventral orientation of the parapophyseal facet (Fig. 8).

Inposteriorview,the twohalvesofthe neuralarcharecon− siderably flattened. The neural spine is robust and cylindrical, remarkablyhighandcolumnar.Theposterodorsalnotchofthe 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 forameninside. The articular surfacesare 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 devel− oped, being considerably higher in some specimens (UFAC− PV 1609, 2952, 2956, 4027, and 5716E), and has an epi− physeal articular facet in the distal end. It is very short antero− posteriorly and its anterior margin is slightly concave, distant from the zygosphene. It is restricted to the posterior extrem− ity 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 diapo− physis is slightly convex and the parapophysis is rather con− cave. The cotyle is strongly prominent in some specimens, where the anterolateral edge surpasses the level of the ante− rior edge of the zygosphene. Small lateral foramina are visi− ble on the lateral walls of the neural arch, more or less posi− tioned 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 sub− central 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 hori− zontally oriented and smooth, where the distance between the two structures is relatively large, due to fact that the neu− ral 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 ori− entated. A small and sharp−edged prezygapophyseal process projects beyond the articular facet of the prezygapophysis. In the posterior trunk vertebra, the prezygapophyses are antero− laterally directed. The postzygapophyses are strongly ori− ented laterally. The interzygapophyseal constriction is well− marked and very short, between the pre− and postzygapo− physis 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 nar− rows 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 fo− ramina, anterolaterally situated and very close together. The subcentral ridges are relatively well marked, extending ap− proximately from the level between the dia−and parapo− physes to the condyle. In the holotype and in UFAC−PV 2952, 3485, 4027, and 5716E, the paradiapophyses are sepa− rated from the ventrolateral edge of the cotyle by a small and shallow notch. In other specimens, this constriction is dis− creet and subtle, probably in part due to the high degree of

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.

(Parte 2 de 4)

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