Thaumastophis missiaeni, Rage & Folie & Rana & Singh & Rose & Smith, 2008
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publication ID |
https://doi.org/ 10.4202/app.2008.0303 |
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persistent identifier |
https://treatment.plazi.org/id/03C0B830-5E54-FFD9-892B-6E6BFC20FD88 |
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treatment provided by |
Felipe |
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scientific name |
Thaumastophis missiaeni |
| status |
sp. nov. |
Thaumastophis missiaeni sp. nov.
Fig. 5 View Fig .
Etymology: After Pieter Missiaen (University of Ghent, Belgium), for his contribution to the Indian Eocene vertebrate project.
Type material: Holotype: One mid−trunk vertebra (VAS 1017). Paratypes: Three vertebrae: two mid− (VAS 1018, 1019) and one posterior trunk (VAS 1020) vertebrae. All from the continental beds of the early Eocene Cambay Formation .
Type locality: Vastan Lignite Mine , northeast of Surat, Gujarat, India .
Type horizon: Early Eocene (middle to late Ypresian) continental beds of Cambay Formation .
Diagnosis.—Differs from all other snakes in having prezygapophyses strongly compressed anteroposteriorly below the articular facets, forming laminar deep prezygapophyseal processes that slightly protrude laterally. Vertebrae lightly built and slightly elongate. Dia− and parapophyseal areas distinct. Neural spine blade−like and long. Centrum narrow, flat ventrally.
Description of the holotype.—The holotype is a slightly damaged mid−trunk vertebra that is lightly built and slightly elongate. Measurements (in mm): width of zygosphene: 2; length of centrum from edge of cotyle to tip of condyle: 3.1; width of interzygapophyseal constriction at narrowest circumference: 2.5.
In anterior view, the vertebra is wide. The zygosphene is thin, wide and slightly arched dorsally. The section of the neural canal is broad, almost as wide as the zygosphene. The cotyle is round and markedly narrower than the neural canal. Small ventrolateral tubercles are present below the cotyle. The prezygapophyses strongly project laterally. The prezygapophyseal processes are deep and they slightly project laterally beyond the prezygapophyseal facets. The prezygapophyseal facets are hardly slanting above the horizontal. The paradiapophyses slightly project below the cotyle. A paracotylar foramen is present on the left side only.
In dorsal view, the vertebra is slightly elongate. The interzygapophyseal constriction is moderately deep. The prezygapophyseal facets are elongate, their major axis being oblique. The anterior border of the zygosphene is concave. The posterior border of the neural arch is damaged. The neural spine is laminar, rather thin and long; it reaches the anterior border of the zygosphene.
In lateral view, the neural spine is rather high; its anterior border arises obliquely from the anterior border of the zygosphene. The prezygapophyseal buttress is strongly compressed anteroposteriorly as a deep lamina below the articular facet; it is recurved posteroventrally and it forms a short prezygapophyseal process. The interzygapophyseal ridge is salient. The paradiapophysis is elongate dorsoventrally; the diapophysis bulges and it is distinct from the clearly flatter and broader parapophysis. The ventral border of the haemal keel is slightly convex ventrally.
In ventral view, the surface of the centrum is flat and narrow. The subcentral ridges are moderately salient but well−marked; they weakly diverge anteriorly. The haemal keel is narrow and slightly widening posteriorly.
In posterior view, the neural arch is rather depressed. Parazygantral foramina are absent.
Intracolumnar variation.—Aside from vertebrae from the mid−trunk region, only one poorly preserved, eroded posterior trunk vertebra is available. It only shows that, as is usual, the paradiapophyses are more distant from the centrum than in mid−trunk vertebrae.
Intraspecific variation.—In one mid−trunk vertebra (VAS 1018), the anterior border of the zygosphene is nearly straight in dorsal view, the anterior border of the neural spine originates posteriorly to the zygosphenal edge, the lamina beneath the prezygapophyseal facet is vertical (not recurved), and the ventral border of the haemal keel is almost straight in lateral aspect. The posterior median notch of the neural arch, not preserved in the holotype, is moderately deep. In VAS 1018, two paracotylar and one parazygosphenal foramina are present on each side. An additional parazygosphenal foramen perhaps opens on the right side,
but this cannot be confirmed. Discussion.— Thaumastophis missiaeni differs from all other snakes by a peculiar character: the prezygapophysis is strongly compressed beneath its articular facet, forming a more or less vertical, deep lamina that projects laterally as a short prezygapophyseal process. This morphology of the prezygapophyses appears to be a derived state unique to Thaumastophis missiaeni . This condition likely represents the highest degree of the compression that occurs in the Palaeophiidae , the Acrochordoidea, and the Anomalophiidae and Russellophiidae . Contrary to other snakes in which compression occurs, in Thaumastophis the prezygapophyses markedly project laterally. The differentiation between dia− and parapophyseal areas points to the Caenophidia . Thaumastophis is the earliest snake in which this character occurs. Aside from these features, the overall morphology of Thaumastophis missiaeni is reminiscent of the colubroids (more specifically, the light build, slight elongation, long and blade−like neural spine and narrow centrum). However, paired paracotylar foramina, coupled with the presence of parazygantral foramina (as observed in VAS 1018), suggest acrochordoids ( Hoffstetter and Gayrard 1964), which renders referral to the colubroids uncertain. Therefore, Thaumastophis missiaeni is assigned to Caenophidia incertae sedis.
Gen. et sp. indet. A
Fig. 2F View Fig .
Material.—Four trunk vertebrae: one (VAS 1006) from the marine beds; three (VAS 1021–1023) from the continental beds. All from the early Eocene Cambay Formation, Vastan Lignite Mine, Gujarat, India.
Description and comparison.—The vertebrae are elongate and relatively gracile, with a large neural canal and a thin, wide and crenate zygosphene. The prezygapophyseal buttresses are not of the compressed type and incipient, boid−like prezygapophyseal processes are present. The neural arch is slightly vaulted; it bears a comparatively high neural spine that occupies its posterior half. The anterior and posterior borders of the neural spine are almost vertical. Paracotylar foramina are perhaps irregularly present in the bottom of deep depressions. VAS 1006 differs somewhat from the three other vertebrae in having more salient subcentral ridges, but this may be an intracolumnar variation.
This terrestrial snake represents a new taxon at the generic and species level, but none of the specimens is sufficiently complete to serve as the holotype. The family assignment is problematic. Because of its light build, this snake may belong to the poorly known primitive complex of the colubroids or to the basal caenophidian assemblage.
Gen. et sp. indet. B
Fig. 2G View Fig .
Material.—One trunk vertebra (VAS 1051) from the continental beds of the early Eocene Cambay Formation, Vastan Lignite Mine, Gujarat, India.
Description and comparison.—This single vertebra is elongate and not massive; the neural canal is large and the zygosphene is thin. The prezygapophyseal buttresses are compressed and there is no prezygapophyseal process. The vertebra lacks paracotylar foramina. The long neural spine reaches the zygosphenal roof anteriorly; its height remains unknown. The centrum is elongate, narrow, without well−marked subcentral ridges. The haemal keel is wide and poorly marked off from the centrum.
On the whole, this vertebra is reminiscent of Procerophis , but it differs from it in lacking prezygapophyseal processes and subcentral ridges, and in being less gracile. Like Procerophis , this specimen may belong to the Colubroidea ; however, based on this single specimen, such a referral cannot be certain. This vertebra, more specifically its centrum, is reminiscent of various extant arboreal colubrids. But as shown by the absence of prezygapophyseal processes, it does not belong to the colubrids.
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