Seismophis septentrionalis, Hsiou & Albino & Medeiros & Santos, 2014

Hsiou, Annie S., Albino, Adriana M., Medeiros, Manuel A. & Santos, Ronny A. B., 2014, The oldest Brazilian snakes from the Cenomanian (early Late Cretaceous), Acta Palaeontologica Polonica 59 (3), pp. 635-642 : 637-638

Seismophis septentrionalis sp. nov.

Fig. 2 .

Etymology: From Latin septentrionalis , from the north, northern, referring to the type locality, which is the northernmost region of Maranhão. Holotype: CPHNA-MA VT-1221, almost complete posterior trunk vertebra.

Type locality: Falésia do Sismito (2º28’43.0”S; 44º28’10.3”W) of Cajual Island, Maranhão, northeastern Brazil .

Type horizon: Cenomanian (early Late Cretaceous), Alcântara Formation, Itapecuru Group, São Luis-Grajaú Basin ( Góes and Rossetti 2001).

Diagnosis.—Snake characterized by low and rather long vertebrae with the following combination of character states: zygosphene moderately thick with a rectilinear roof; strongly marked parasagittal ridges of the neural arch; parazygantral foramina present; deep interzygapophyseal constriction; low, long, and anteroposteriorly elongate neural spine; prezygapophyseal process absent; paracotylar foramina absent; centrum broader anteriorly than posteriorly, with well-defined and sinuous subcentral ridges; and well-defined, broad, and flattened haemal keel.

Description.—The holotype is a posteriormost trunk vertebra as evidenced by the deep subcentral grooves, and also because it displays prominent lateroventral expansions of the paradiapophyseal facets. In general, it is a very small and delicate vertebra, low, longer than wide, with the centrum somewhat longer than the neural arch width (cl> naw), and depressed, wider than the long neural arch (pr-pr> pr-po). The vertebra lacks the distal end of the neural spine, and the condyle, and both paradiapophyses are eroded.

In anterior view, a wide and moderately thick zygosphene with short articular facets is seen. The width of the zygosphene is almost equal to the transverse diameter of the cotyle (zw ≈ ctw) and shows a rectilinear roof that is not elevated in the middle. The prezygapophyses are somewhat inclined above the horizontal plane, but do not reach the level of the zygosphene. There is no evidence of prezygapophyseal processes. The cotyle is nearly circular (ctw~cth) and there are no paracotylar foramina, only a deep fossa on each side of the cotyle. Paradiapophyses are lateroventrally expanded, where the diapophyses almost reach the prezygapophyseal tip. Although eroded, the parapophyses do not seem to have reached the cotylar rim ventrally.

In dorsal view, the articular facets of the prezygapophyses are broad and subtriangular, with the main axis anterolaterally oriented. The roof of the neural arch shows a strong pronounced ridge joining the lateral edge of the zygosphene and the posteromedial margin of the postzygapophysis on each side of the neural spine. The neural spine is anteroposteriorly elongate and extends all along the roof of the neural arch, but its distal end is broken. Anteriorly it looks as a thin keel, but it is posteriorly enlarged as a robust tubercle. The posterodorsal notch of the neural arch is weakly defined and shallow, without a clearly defined median bay ( Rage 1996). The interzygapophyseal ridges are long, strongly salient and curved.

In posterior view, the neural arch roof is depressed, with the two halves inclined but not vaulted. The zygantrum is deep, with small zygantral foramina. Small parazygantral foramina are present in shallow depressions lateral to the zygantrum, one on each side. The postzygapophyses are slightly inclined dorsally. The condyle is nearly circular cow~coh), with the main axis slightly inclined upward. In lateral view, the centrum is longer than the neural arch, and the vertebra looks depressed. The neural spine is low and elongate anteroposteriorly. The subcentral ridges are narrow and well defined. Small lateral foramina are present on each lateral wall of the neural arch.

In ventral view, the centrum is elongate and widens anteriorly. The well-marked subcentral ridges are sinuous and diverge anteriorly. The haemal keel is clearly defined laterally by deep subcentral grooves. It is flattened, very wide, and occupies much of the ventral surface of the centrum. It originates at the ventral edge of the cotyle and becomes more prominent in the mid-portion of the centrum. From there on, it widens significantly, almost reaching the same width of the condyle. Posteriorly, it reaches the precondylar constriction, which is moderately marked. There is a pair of small subcentral foramina, one on each side, hidden on the lateral surface of the haemal keel. The postzygapophyses show broad subtriangular articular facets.

Figures

Fig. 2. Trunk vertebra of the snake Seismophis septentrionalis gen et sp. nov. (CPHNA-MA VT 1221) from the Cenomanian (early Late Cretaceous) of Falésia do Sismito, Cajual Island, Maranhão, northeastern Brazil. Photographs (A –E) and explanatory drawings (A –E), in anterior (A), posterior (B), 1 1 2 2 lateral (C), dorsal (D), and ventral (E) views.