Caraiba andreae ( Reinhardt and Lütken, 1862 )

Syromyatnikova, Elena, Aranda, Ernesto & González, Soraida Fiol, 2021, First insight into the diversity of snakes in the Pleistocene of Cuba, Acta Palaeontologica Polonica 66 (2), pp. 395-407 : 401-403

cf. Caraiba andreae ( Reinhardt and Lütken, 1862)

Fig. 4B .

Material.—30 precloacal vertebrae (PIN 5782/36–65), VI and VII layers, late Pleistocene, El Abrón Cave, Cuba.

Description.—The vertebrae are relatively small, with a centrum length ranging 1.8–2.5 mm ( Fig. 4B ; PIN 5782/36). They are elongated (longer than wide, ratio CL/NAW is 1.5) and lightly built. In dorsal view, the interzygapophyseal constriction is well developed ( Fig. 4B 1 ). The neural spine is thin along its dorsal margin. The zygosphene is three-lobed, with lobes which are relatively poorly developed. The prezygapophyseal facets are elongate in outline. The prezygapophyseal processes are well developed and anterolaterally oriented with rounded tips, their length reaches more than half the length of the prezygapophyseal facets. In ventral view, the haemal keel is prominent and relatively thin, only slightly widened posteriorly ( Fig. 4B 2 ). It is accompanied by shallow subcentral grooves. The subcentral ridges are low. Two small subcentral foramina are present on each side of the haemal keel. In lateral view, the neural spine is low, with a straight dorsal margin ( Fig. 4B 3 ). Its anterior end only slightly overhangs anteriorly, but the posterior end clearly overhangs posteriorly. The haemal keel is clearly visible, straight ventrally and pointed posteriorly. The synapophyses have distinct parapophyseal and diapophyseal portions of nearly similar size. The lateral foramina are clearly visible. In anterior view, the zygosphene is somewhat convex dorsally ( Fig. 4B 4 ). The neural canal is relatively large and nearly the same height as the height of the cotyle. It is wider at the bottom than at the top. The prezygapophyseal facets are nearly horizontal, whereas the prezygapophyseal processes are often directed slightly ventrally. The cotyle is dorsoventrally compressed. The paracotylar foramina are present. In posterior view, the neural canal is relatively large and high, and the neural arch is vaulted ( Fig. 4B 5 ). The condyle is more rounded than the cotyle.

Remarks.—The described vertebrae are assigned to Dipsadidae based on elongated centrum, presence of haemal keel instead of hypapophysis, and clearly divided synapophyses Holman 1979, 1981, 2000). The vertebrae can be distinguished from those assigned to Arrhyton (see above) based on having larger size, elongated proportions, long prezygapophyseal processes, low and thin neural spine, poorly convex zygosphene, and more vaulted posteriorly neural arch. They are identical in morphology and size to Recent Caraiba andreae ( Fig. 4C ; PIN H 105). They differ from the large Cubophis by having a low neural spine (see Mead and Steadman 2017). Caraiba is a moderately-sized racer of Cuba. Only C. andreae is known ( Powell and Henderson 2012), and it is distributed widely across the territory of the island ( Rodríguez-Schettino et al. 2013). It is highly probable that the described fossils belong to this snake.

Dipsadidae indet.

Fig. 5A .

Material.—One precloacal vertebra (PIN 5782/82), VII layer, late Pleistocene, El Abrón Cave, Cuba.

Description.—The vertebra PIN 5782/82 ( Fig. 5A ) is relatively small and elongated, but strongly built, with a centrum length of 3.1 mm and CL/NAW ratio of 1.5. In dorsal view, the interzygapophyseal constriction is clear and anteroposteriorly long ( Fig. 5A 1 ). The zygosphene is narrow and bears a crenate anterior margin with two small lateral lobes, and wide, but poorly protruding anteriorly median lobe. The neural spine is markedly thickened along the dorsal margin. Its posterior end is rounded, and although the anterior one is slightly damaged, it can be reconstructed as bifurcated. The prezygapophyseal facets are oval in outline. The prezygapophyseal processes (only the left one is preserved) are massive, greatly expanded dorsoventrally and obtuse distally. Its length is less than half that of the facets. The prezygapophyseal processes are directed anterolaterally, extend beyond the level of facets. In ventral view, the subcentral area is moderately wide ( Fig. 5A 2 ). It bears a haemal keel which is flattened ventrally, spatulate-shaped, and extremely widened posteriorly where it is almost as wide as the condyle. Two wide, paired tubercles are present below the cotylar rim. The subcentral grooves and subcentral ridges are poorly developed. The subcentral foramina are small and positioned a distance from a haemal keel. In lateral view, the neural spine is low with a slightly rounded dorsal margin ( Fig. 5A 3 ). The anterior and posterior margins of the neural spine overhangs the cotyle and condyle. The haemal keel is poorly protruded ventrally, and even looks concave in its ventral margin. The synapophysis on the left side is elongated and has distinct parapophyseal and diapophyseal portions, whereas the synapophysis on the right side is greatly enlarged and robust, its parapophyseal and diapophyseal portions are fused (probably due to pathology). The lateral foramina are small. In anterior view, the zygosphene is convex. Its dorsolateral parts are thickened and bend dorsally ( Fig. 5A 4 , marked by arrow). The neural canal is tunnel-like, and its dorsoventral height is nearly the same as the dorsoventral height of the cotyle. The prezygapophyseal facets are approximately horizontal. The cotyle is flattened. Two tubercles are visible below the cotylar rim. The paracotylar foramina are minute. In posterior view, the neural arch is moderately vaulted ( Fig. 5A 5 ). The neural canal is the same shape as it is in anterior view. The condyle is slightly flattened.

Remarks.—PIN 5782/82 is elongated and has a haemal keel and divided synapophysis, and thus, it can be assigned to Dipsadidae . It is similar to the group of North American “xenodontines” in having a wide haemal keel (sensu Holman 1979). The combination of its other characters (extremely widened posteriorly haemal keel, dorsoventrally expanded prezygapophyseal processes, rounded and widened dorsally neural spine overhanging anteriorly and posteriorly) was not observed in other taxa described above and in other known Cuban snakes. The thickened and dorsally bent dorsolateral part of the zygosphene was not mentioned in other known extinct and extant colubrids. The shape of haemal keel and low neural spine of PIN 5782/82 are somewhat similar to Carphophis Gervais in d’Orbigny, 1843 (see Holman 2000), however, in other features (general proportions, shape of zygosphene, thickened neural spine, etc.) PIN 5782/82 differs from that snake. In some characters (massive, dorsoventrally expanded and obtuse distally prezygapophyseal processes and rounded and dorsally widened neural spine overhanging anteriorly and posteriorly) PIN 5782/82 is similar to some Lampropeltis spp. ( Holman 2000: 170; Jim Mead, personal communication 2020). The broad and flattened haemal keel may also suggest that PIN 5782/82 belongs to the posterior precloacal portion of the vertebral column. As this peculiar vertebral morphology is observed only in the single specimen, its systematic allocation cannot be fully demonstrated. Pending the discovery of additional material and a better comprehension of the vertebral morphology of Dipsadidae , the described specimen is herein tentatively assigned to Dipsadidae indet.

Natricidae Boettger, 1883

Natricidae indet.

Fig. 5B .

Material.—One precloacal vertebra (PIN 5782/83), VI layer, late Pleistocene, El Abrón Cave, Cuba.

Description.—The vertebra PIN 5782/83 ( Fig. 5B ) is almost complete and has a slightly damaged posterior margin on the neural arch and synapophyses. It is small and elongated, with a centrum length of 2.2 mm and ratio CL/NAW of 1.7. In dorsal view, the interzygapophyseal constriction is well developed ( Fig. 5B 1 ). The zygosphene bears a protruding median lobe, delimited laterally with two smaller but distinct lobes. The neural spine is long, reaching the roof of the zygosphene, but it does not approach its anterior bor- der. Its dorsal margin is thin. The prezygapophyseal facets are roundish and the prezygapophyseal processes are short (about 1/3 of the length of the prezygapophyseal facets), anterolaterally directed and distally pointed. In ventral view, the centrum has a fully preserved hypapophysis ( Fig. 5B 2 ). It is laterally compressed, and homogeneous in width along its entire length. The subcentral grooves and subcentral ridges are shallow. The subcentral foramina are moderate in size. In lateral view, the neural spine is low, with a straight dorsal margin ( Fig. 5B 3 ). The anterior and posterior margins of the neural spine are only slightly inclined. The hypapophysis protrudes beyond the level of the condyle and is directed posteriorly rather than ventrally. Along the ventral border it is slightly sinusoidal. The tip of the hypapophysis is rather acute. Although damaged, the parapophysis and diapophysis have a nearly similar diameter. The lateral foramina are well developed. In anterior view, the zygosphene is wide (wider than cotyle) and arched dorsally ( Fig. 5B 4 ). The neural canal is nearly subcircular. Its dorsoventral height is less that the dorsoventral height of the cotyle. The prezygapophyseal facets are horizontally oriented. The paracotylar foramina are indistinct. In posterior view, the neural arch is moderately vaulted ( Fig. 5B 5 ). The neural canal is slightly higher than it is in anterior view. The condyle is similar to the cotyle in outline.

Remarks.—PIN 5782/83 is somewhat similar to anterior precloacal vertebrae (= cervicals) of Caraiba andreae in general proportions and presence of the hypapophysis. Within the anterior precloacal vertebrae of C. andreae , the most anterior ones have a ventrally directed hypapophysis, whereas the most posterior vertebrae have a posteriorly directed hypapophysis, similar to those observed in PIN 5782/83. However, PIN 5782/83 differs from all cervicals of Caraiba in low and long neural spine, distally pointed prezygapophyseal processes, and not anteriorly directed parapophyseal processes. PIN 5782/83 comes from the middle precloacal region rather than from anterior precloacal region. Based on the presence of a hypapophysis, PIN 5782/83 can be assigned to Natricidae , Viperidae , or Elapidae ( Szyndlar 1991b) . In Viperidae , however, the longer hypapophysis is directed more ventrally than posteriorly, the neural arch is typically more depressed, the parapophyseal processes distinctly longer, and vertebral centrum is shorter. PIN 5782/83 shares some traits of Elapidae , sharing the low neural spine and the presence of a non-sigmoid hypapophysis. In PIN 5782/83 the axis of the hypapophysis lies at an acute angle to the vertebral axis, which is typical for small-sized Elapidae such as the species of Micrurus Wagler in Spix, 1824 (see Auffenberg 1963; Rage and Holman 1984). As in Micrurus, PIN 5782/83 has small dimensions, an elongate centrum, neural spine that tends to be undercut both anteriorly and posteriorly, a slender and compressed hypapophysis projecting posteriorly beyond the tip of the condyle, and wide neural canal in comparison with the cotyle (e.g., Auffenberg 1963; Rage and Holman 1984; Szyndlar and Schleich 1993). The hypapophysis in PIN 5782/83 has an unusual shape because of its sinusoidal ventral border, whereas in elapids the hypapophysis is straight ventrally. The presence of Elapidae in Cuba would also be unexpected because there are no fossil or Recent elapids in the Greater Antilles.

PIN 5782/83 rather belongs to Natricidae , based on the posteriorly vaulted neural arch, short parapophyseal processes, and long centrum.Of the natricid snakes, only Nerodia clarkii is known in the present-day fauna of Cuba, but the vertebrae of N. clarkii clearly differ from PIN 5782/ 83 in having a shorter centrum, high neural spine, and more ventrally directed hypapophysis ( Mead and Steadman 2017: fig. 4.1). PIN 5782/83 cannot be assigned to Neonatrix Holman, 1973 , due to the long hypapophysis extending beyond the condyle ( Holman 2000). In contrast to Nerodia and Neonatrix , the vertebrae of Thamnophis Fitzinger, 1843 , are characterised by their small size, elongated centra, and low and long neural spine ( Parmley 1988). The vertebrae of Thamnophis , however, usually bear a slightly higher neural spine ( Auffenberg 1963; Holman 2000). According to Auffenberg (1963), PIN 5782/83 is similar to the snakes of Group I (i.e., vertebrae with a long centrum and a low, long neural spine) of the New World natricid snakes, which includes Storeria Baird and Girard, 1853 , Tropidoclonion Cope, 1860 , and Virginia Baird and Girard, 1853 . The generic differentiation of these taxa is difficult because these small snakes are similar in vertebral morphology ( Parmley and Hunter 2010). For this reason, and because only one specimen was found, we tentatively assign PIN 5782/83 to Natricidae indet.

Figures

Fig. 4. Precloacal vertebrae of Dipsadidae from Cuba, Recent (C) and the Late Pleistocene, El Abrón Cave (A, B). A. Arrhyton sp., PIN 5782/23, in dorsal (A1), ventral (A2), lateral (A3), anterior (A4), and posterior (A5) views. B. cf. Caraiba andreae, PIN 5782/36, in dorsal (B1), ventral (B2), lateral (B3), anterior (B4), and posterior (B5) views. C. Caraiba andreae (Reinhardt and Lütken, 1862), PIN H 105, in dorsal (C1), ventral (C2), lateral (C3), anterior (C4), and posterior (C5) views.

Fig. 1. A. Geographic location of the studied area.B. The locality El Abrón Cave, Cuba (arrowed).

Fig. 2. Precloacal vertebrae of Typhlopidae (A) and Tropidophiidae (B–D) from Cuba, Recent (C) and the Late Pleistocene of El Abrón Cave (A, B, D). A. cf. Cubatyphlops, PIN 5782/1, in dorsal (A1), ventral (A2), lateral (A3), anterior (A4), and posterior (A5) views. B. Tropidophis melanurus (Schlegel, 1837), PIN 5782/5, in dorsal (B1), ventral (B2), lateral (B3), anterior (B4), and posterior (B5) views. C. Tropidophis melanurus Schlegel, 1837, PIN H 103, precloacal vertebra, in dorsal (C1), ventral (C2), lateral (C3), anterior (C4), and posterior (C5) views. D. Tropidophis sp., PIN 5782/12, in dorsal (D1), ventral (D2), lateral (D3), anterior (D4), and posterior (D5) views.

Fig. 3. Precloacal vertebrae of Cubophis spp. from Cuba, Recent (C) and the Late Pleistocene, El Abrón Cave (A, B). A. Cubophis cf. cantherigerus, PIN 5782/66, in dorsal (A1), ventral (A2), lateral (A3), anterior (A4), and posterior (A5) views. B. Cubophis cf. cantherigerus, PIN 5782/67, in dorsal (B1), ventral (B2), lateral (B3), anterior (B4), and posterior (B5) views. C. Cubophis cantherigerus (Bibron, 1840 in Ramón de la Sagra 1838–1843), PIN H 104, in dorsal (C1), ventral (C2), lateral (C3), anterior (C4), and posterior (C5) views.

Fig. 5. Precloacal vertebrae of Dipsadidae indet.and Natricidae indet. from the Late Pleistocene, El Abrón Cave, Cuba.A. Dipsadidae indet., PIN 5782/82, in dorsal (A1), ventral (A2), lateral (A3), anterior (A4), and posterior (A5) views.Arrow marked the thickened and bend dorsally dorsolateral parts of the zygosphene. B. Natricidae indet., PIN 5782/83, in dorsal (B1), ventral (B2), lateral (B3), anterior (B4), and posterior (B5) views.