Russellophis crassus, 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/03C0B830-5E5F-FFD5-897E-6EF3FD0DFABE |
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treatment provided by |
Felipe |
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scientific name |
Russellophis crassus |
| status |
sp. nov. |
Russellophis crassus sp. nov.
Fig. 3 View Fig .
Etymology: Latin crassus , thick,in reference to the vertebral morphology.
Type material: Holotype: One mid−trunk vertebra (VAS 1039). Paratypes: Eight vertebrae: six trunk (VAS 1011, 1012, 1040–1042, 1056) and two caudal (VAS 1013, 1043) vertebrae. All from the continental beds of the early Eocene Cambay Formation .
Other material: Two larger trunk vertebrae (VAS 1044, 1045) from the continental beds may represent overgrown specimens, but their assignment to the species cannot be confirmed.
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 Russellophis tenuis and Krebsophis thobanus Rage and Werner, 1999 in having a narrower and thicker zygosphene. Further differs from R. tenuis by its more massive build, larger cotyle and condyle, and more dorsally placed paradiapophyses. Further distinguished from K. thobanus by its lamellar and high neural spine, paradiapophyses more extended dorsoventrally, thinner roof of zygantrum, and by the continuity between ventral edge of parapophyses and subcentral ridges.
Description of the holotype.—The holotype is a nearly complete mid−trunk vertebra whose measurements are as follows (in mm): width through prezygapophyses: 4.3; width of zygosphene: 1.6; length of centrum from edge of cotyle to tip of condyle: 3.9; width of interzygapophyseal constriction at narrowest circumference: 2.5.
In anterior view the vertebra is not depressed. The zygosphene is thick and relatively narrow, its roof is concave dorsally, a thin horizontal median lobe standing out against the bulk of the zygosphene. The section of the neural canal is low and nearly as wide as the zygosphene. The cotyle is almost circular, its width being similar to those of the zygosphene and neural canal. The prezygapophyses strongly project laterally, they lack any trace of prezygapophyseal processes. The prezygapophyseal articular facets are slightly inclined below the horizontal. The paradiapophyses are located rather low but they do not protrude clearly below the cotyle and they face somewhat ventrally. The paracotylar foramina are absent.
In dorsal view, the vertebra is markedly elongate. The interzygapophyseal constriction is shallow and asymmetrical, its most constricted part being shifted anteriorly. The prezygapophyseal facets are nearly circular, without a discernible major axis. The anterior border of the zygosphene forms three weakly projecting lobes (a wide median lobe and narrow lateral ones). The shape of the posterior median notch is obscured by matrix, but it is probably not shallow. The neural spine is lamellar and composed of two portions: a posterior thick part occupying less than one−third of the vertebral length and a thinner anterior part reaching the posterior limit of the zygosphenal roof.
In lateral aspect, the posterior, thick part of the neural spine is rather high. The zygosphenal facets are broad and situated markedly above the zygapophyseal plane. The prezygapophyseal buttress is compressed; it forms a ridge that reaches the lateral tip of the articular facet. A small anterior tubercle is present on this ridge at the level of the top of the paradiapophysis; the tubercle is prolonged posteriorly as a blunt ridge on the lateral face of the buttress. The interzygapophyseal ridge is very salient. The paradiapophysis is rather small and strongly inclined, the top of the diapophysis being located approximately below the posterior limit of the prezygapophyseal facet; the articular surface is not subdivided into dia− and parapophyseal areas. The subcentral ridge is well−marked and arched dorsally. The lateral foramina are present.
In ventral view, the surface of the centrum is narrow, flat, limited laterally by well−defined subcentral ridges that hardly diverge anteriorly. The ventral rim of each parapophysis extends posteriorly and grades into the subcentral ridge. The haemal keel is of moderate width; its ventral edge is blunt.
In posterior view, the neural arch is very vaulted and it swells out above the zygantrum. The roof of the zygantrum is thin. Parazygantral foramina are absent.
Intracolumnar variation.—One vertebra (VAS 1011), from the transition between the anterior and mid−trunk regions, differs from the holotype, i.e., from mid−trunk vertebrae, in having a wider zygosphene, a narrower and deeper haemal keel, less marked subcentral ridges, and paradiapophyses projecting below the cotyle. Posterior trunk vertebrae have the neural arch less vaulted than in more anterior vertebrae (but it remains markedly vaulted). Their haemal keel is wider and more poorly defined in the posterior half of centrum; it is anteriorly limited by short and narrow subcentral grooves. The caudal vertebrae retain a very vaulted neural arch; they differ from posterior trunk ones only in having pleurapophyses (or lymphapophyses) and haemapophyses. It should be noted that there is no conspicuous variation in length or height of the neural spine within the vertebral column.
Intraspecific variation.—The prezygapophyseal facets may be horizontal or slightly inclined either below the horizontal or (in one vertebra) above the horizontal. The tubercle on the anterior face of the prezygapophyseal buttress is not always present. In lateral aspect, the long axis of the paradiapophysis is strongly inclined (e.g., the holotype) or less inclined. These variations are apparently not correlated with the position of the vertebrae in the vertebral column. One feature that cannot be seen on the holotype is observable on other vertebrae: the posterior median notch in the neural arch is deep.
Discussion.— Russellophis crassus displays all features of the Russellophiidae (see above). It clearly differs from Russellophis tenuis and Krebsophis thobanus , the only other known species of the family. The narrow and deep zygosphene sharply distinguishes R. crassus from the two other species in which it is wide to very wide and thin. In addition, although this cannot be regarded as a specific feature, R. crassus is larger than K. thobanus and R. tenuis . In the largest vertebra of R. crassus (VAS 1012) , the length of the centrum reaches 3.8 mm although the extremity of the condyle is broken off (it was probably over 4 mm); this measurement is 3.3 mm and 3.6 mm in the largest vertebrae of K. thobanus and R. tenuis , respectively.
R. crassus is further distinguished from R. tenuis by its markedly more massive build, its larger cotyle and condyle, and its less ventrally placed paradiapophyses. In addition, in some vertebrae of R. crassus the axis of the paradiapophyses is more inclined posterodorsally than in R. tenuis . The tubercle that occurs on the anterior face of the prezygapophysis may be absent in R. crassus , whereas it is always present in R. tenuis (although sometimes unilaterally).
R. crassus differs from K. thobanus in having a lamellar and rather high neural spine, paradiapophyses more extended dorsoventrally, and a markedly thinner roof of the zygantrum despite the massive build of the vertebrae. Moreover, in R. crassus , as in R. tenuis , the ventral edge of each parapophysis is continuous with the subcentral ridge; in K. thobanus , the parapophysis appears to be distinct from the ridge.
Rage and Werner (1999) distinguished Krebsophis from R. tenuis on the basis of the following characters: (1) vertebrae of Krebsophis more heavily−built, although the size is similar; (2) cotyle and condyle larger in Krebsophis ; (3) neural spine, a low keel for most of its length in Krebsophis , a rather high lamina in R. tenuis ; (4) paradiapophyses more dorsally placed in Krebsophis ; (5) interzygapophyseal and subcentral ridges more prominent in Krebsophis .
R. crassus displays features that occur either in Krebsophis or R. tenuis . Among the features listed above, it shares characters 1, 2, 4, and 5 with Krebsophis . Only character 3 is common to R. crassus and R. tenuis . However, character 5 directly results from the massiveness (character 1) of the vertebrae; these two characters should not be regarded as distinct. On the other hand, two characteristics shared by R. crassus and R. tenuis should be added: the thin zygantral roof and the connection between the ventral rim of parapophysis and subcentral ridge. Another character may discriminate between Krebsophis on one hand, and R. crassus and R. tenuis on the other hand: in Krebsophis , the dorsoventral extent of the paradiapophysis seems reduced, whereas in the two other species it is “normal”. Finally, on the basis of the morphology of the neural spine, the relation between paradiapophyses and subcentral ridges, the morphology of paradiapophyses, and the thin zygantral roof, the species from Vastan is tentatively referred to Russellophis .
? Russellophiidae gen. et sp. indet.
Fig. 2E View Fig .
Material.—One trunk vertebra (VAS 1050) from the continental beds of the early Eocene Cambay Formation, Vastan Lignite Mine, Gujarat, India.
Description and comparisons.—This vertebra is characterized by its very strong, unusual elongation. The ventral face of the centrum is very narrow, flat, and limited by poorly marked subcentral ridges; contrary to what is usual in snakes, the ridges are more apparent in the posterior part of the vertebra than anteriorly. The haemal keel is very thin. The prezygapophyseal buttress is identical to that of russellophiids and a small anterior tubercle is present. The prezygapophyseal facets are inclined below the horizontal. The zygosphene is approximately as wide as the cotyle and its roof is concave dorsally. The paradiapophyses are situated low and they face rather ventrally. The neural spine is restricted to the posterior part of the neural arch; it is prolonged anteriorly by a faint ridge. The neural arch is very vaulted.
This vertebra is astonishing. Its elongation is reminiscent of that of extant highly arboreal colubrids. On the other hand, aside from strong elongation, it displays a combination of characters that is typical of the Russellophiidae (see above). Only the poor development of the subcentral ridges is not characteristic of russellophiids. The anterior face of the specimen, with a zygosphene as wide as the cotyle and concave dorsally, is consistent with that of Russellophis crassus . Therefore, VAS 1050 might be interpreted as a posterior trunk vertebra of this species, because vertebrae of the posterior trunk region (but not the posteriormost ones) are more elongated than those of the mid−trunk. However, this vertebra is markedly more elongate than the caudal vertebrae of R. crassus , so assignment to this taxon does not appear to be possible. In Europe, no such vertebra has been found despite the fact that Russellophis is relatively frequent in the Eocene.
Colubroidea indet.
Genus Procerophis nov.
Etymology: Latin procerus, elongate, in reference to the vertebral morphology.
Type species: Procerophis sahnii sp. nov. from Vastan Lignite Mine , northeast of Surat, Gujarat, India; monotypic .
Diagnosis.—As for the type and only known species.
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