The fossil studied was collected in Geda Cavern, located in Sierra de Guasasa, karst massif of Jurassic gray limestones, 6 km North of the Viñales town, Pinar del Río province, Cuba (Fig. 1). Its main access (22.6541N, 83.7139W) is located on the western slope of the mountain, at a height of 70 m above the level of the San Vicente Valley and 210 m a.s.l. The cavern has two levels of locally superimposed main galleries. The lower one is separated into two sections, the first one communicates with the main access and constitutes a practically rectilinear gallery of 1.2 km in length, oriented in an approximate east-west direction. The second section of the lower level presents a gallery of approximately 600 m in length.

The two levels exhibit little meanders, more numerous in the upper level, suggesting the transfluence flow character of the cavity in the early stages of its formation. Secondary formations, clay, carbonated or gypsum sediments cover the pavement of both levels. The upper level is particularly abundant in calcite speleothems (Condis, 2010Condis, M. (2010) Inferencias paleoecológicas sobre especies de la mastofauna cuaternaria cubana, conservadas en el depósito superficial de La Caverna Geda, Pinar del Río, Cuba. [Doctoral thesis. University of Pinar del Río, Cuba, and University of Alicante].). The vertebra of Amphisbaenia was collected in the lower level, in a clayed area where eroded bone fragments were excavated, some stained with dark pigments of chemical elements contained in local groups of ultrabasic rocks (serpentinite).

The bone material was extracted by manual collection and cleaned. It was deposited in the Zoological Collection of the Cuban Academy of Sciences (CZACC), currently Institute of Ecology and Systematics. The osteologic nomenclature follow Zangerl (1945)Zangerl, R. (1945). Contributions to the Osteology of the Post-Cranial Skeleton of the Amphisbaenidae. The American Midland Naturalist, 33(3), 764-780., Bolet et al. (2014)Bolet, A., Delfino, M., Fortuny, J., Almécija, S., Robles J.M. and Alba. D.M. (2014). An amphisbaenian skull from the European Miocene and the evolution of Mediterranean worm lizards. PLoS ONE, 9(6)., and Benites (2015)Benites, J.P. (2015) Estudio comparativo de restos fósseis e recentes de Amphisbaenia. Abordagens filogenéticas, Paleoecológicas, Paleobiogeográficas. [Master thesis. Institute of Geosciences and Exact Sciences, Paulista State University]. , and the taxonomy is according to Kearney (2003)Kearney, M. (2003). Systematics of the Amphisbaenia (Lepidosauria: Squamata) Based on Morphological Evidence from Recent and Fossil Forms. Herpetological Monographs, 17(2003), 1-74., and Gans (2005)Gans, C. (2005). Checklist and Bibliography of the Amphisbeania of the wolrd. Bulletin American Museum of Natural History, 289, 130..

Fossil was photographed with a stereomicroscope Leica M205a equipped with a digital camera DFC425 using the software Leica Application Suite (3.8). Proportions of exemplars were obtained by measurements relationships. Measurements were made using the software TPSdig (v 2.11).

The vertebra is rather small (1.91 mm of body length), dorso-ventrally compress in general aspect, constricted in dorsal view between the pre- and postzygapophyses show all margins smooth. It lacks left prezygapophyses. Right prezygapophysis is antero-dorsally directed, about 20° up with respect to the transversal axis, and 45° with respect to the longitudinal axis. Articular surfaces are drop-shaped and face upward. It presents a large, blunt prezygapophyseal process, slightly less wide than the articular surface.

Synapophyses are massive and globular, ventro-laterally directed, and well-defined from the vertebral body. The interzygapophyseal constriction is deep, almost half the width of the distance between postzygapophyses. It describes a regular curve without angulation. Postzygapophyses open laterally, about 22° with respect to the horizontal axis. Articular facets are dorsally sloped, about 28° with respect to the transversal axis. Articular surfaces are drop-shaped as that of the prezygapophyses.

Dorsal surface is smooth. The neural spine is absent, but a sort of sagittal ridge is developed. Neural arc describes a convex curve, being more evident in anterior view than in posterior. There is no zygantra, nor zygosphene. In dorsal view, the anterior edge of the neural arch is almost straight; it lacks pars tectiformis, whereas posterior edge is mid notched. The median notch is delimited both sides by a small convexity. Dorsal surface of the arch surrounding such median notch form a ridge V-shaped opening backward.

Neural canal has a semicircular shape, dorso-ventrally compressed anteriorly, and laterally compressed posteriorly. Posterior output is higher and wider than anterior. Due to sediment incrustations, it cannot be seen if paracotylar foramen is present. Ventral surface of the centrum is entirely flat and wide, without hemal keel, instead it presents a mid-shallow groove. Lateral edges are almost parallel from the cotyle to the condyle. Both sides in anterior third of the body appear the outline of two foramina subcentralia.

Both, the cotyle and condyle, are dorso-ventrally flattened, they are twice as wide as high. In ventral view, the lower rim of the cotyle is regularly concave and posteriorly placed as compared to the dorsal rim. Condyle is moderately inclined dorsally, with an articular surface slightly visible in ventral view. That is why dorsal edge of the condyle is placed more posteriorly than the ventral edge.

We can assume the vertebra as Amphisbaenian by the following characters: vertebra generally depressed, condyle is transversely widened, and the ventral face of the centrum is flat and has parallel lateral borders; and neural spines are lacking in the trunk region (Hoffstetter and Gasc, 1969Hoffstetter, R. and Gasc, J.P. (1969). Vertebrae and Ribs of Modern Reptiles. In: Gans, C., Bellairs, A. and Parsons, T. (Eds.) Biology of the Reptilia: Vol. I. (pp. 201-210). Academic Press.). Also, the presence of a V-shaped ridge in the posterior medial margin of the neural arc is typical of amphisbaenian vertebrae (Blain et al., 2010Blain, H.A., Canudo, J.I., Cuenca-Bescós, G. and López-Martínez, N. (2010). Amphibians and squamate reptiles from the latest Maastrichtian (Upper Cretaceous) of Blasi 2 (Huesca, Spain). Cretaceous Research, 31(4), 433-446.; Bolet et al., 2014Bolet, A., Delfino, M., Fortuny, J., Almécija, S., Robles J.M. and Alba. D.M. (2014). An amphisbaenian skull from the European Miocene and the evolution of Mediterranean worm lizards. PLoS ONE, 9(6).). Only Amphisbaenidae and Cadeidae families are known from the Antilles, it is correct to think that the Quaternary fossil belong to one of them, However, until now, there is no diagnostic characters in amphisbaenian vertebrae that provide a differentiation among these families present in the Antilles (Scanferla et al., 2006Scanferla, C.A., Montero, R. and Agnolín, F.L. (2006). The first fossil record of Amphisbaena heterozonata from the late Pleistocene of Buenos Aires province, Argentina. South American Journal of Herpetology, 1(2), 138-142.; Mandriola et al., 2011Mandriola, L.F., Delfino, M., Bailon, S. and Pitruzzella. G. (2011). The Late Pliocene amphibians and reptiles from “Capo Mannu D1 Local Fauna” (Mandriola, Sardinia, Italy). Geodiversitas, 33(2), 357-382. ; Rage et al., 2013Rage, J.C., Pickford, M. and Senut, B. (2013). Amphibians and squamates from the middle Eocene of Namibia, with comments on pre-Miocene anurans from Africa. Annales de Paleontologie, 99(3), 217-242.; Bolet et al., 2014Bolet, A., Delfino, M., Fortuny, J., Almécija, S., Robles J.M. and Alba. D.M. (2014). An amphisbaenian skull from the European Miocene and the evolution of Mediterranean worm lizards. PLoS ONE, 9(6).).

In comparing the fossil with Cadea and Amphisbaena vertebrae from the same region of the body (Fig. 2), we find that the fossil presents a projected and rounded prezgapophyseal process, as observed in Cadea, Amphisbaena has a little development of this process. In the fossil as in Cadea, the synapophysis has an oval, massive shape, with almost the prezygapophysis width, different from Amphisbaena where the synapophysis is almost spherical, less massive, and almost half of prezygapophysis width. This two features bring the fossil closer to Cadea genus, although Syromyatnikova et al. (2020)Syromyatnikova, E., Aranda, E. and González, S.F. (2020). The First Fossil Record of Cadea (Amphisbaenia, Cadeidae) and other Amphisbaenian Remains from the Upper Pleistocene of Cuba. Journal of Vertebrate Paleontology, 39(6), e1729167. already pointed out that there is a morphological overlap between the vertebrae of the two families that makes it even more difficult to distinguish them.

Geda Cavern is relevant as a paleontological locality, due to the content, typology and conservation of its fossil fauna record, being in addition, a type locality of the extinct phyllostomid bat Cubanycteris silvai (Mancina and García-Rivera, 2005Mancina, C.A. and García-Rivera, L. (2005). New genus and species of fossil bat (Chiroptera: Phyllostomidae) from Cuba. Caribbean Journal of Science, 41(1), 22-27.). In the sediments that contained the vertebra of Amphisbaenia, paleontological remains of amphibian (Peltophyrne sp.), reptiles (Anolis sp.), undetermined birds, and mammals (Acratocnus antillensis, Parocnus browni, Megalocnus rodens, Neocnus gliriformis, Geocapromys columbianus, Mesocapromys sp., and Capromys pilorides) were identified (Condis, 2010Condis, M. (2010) Inferencias paleoecológicas sobre especies de la mastofauna cuaternaria cubana, conservadas en el depósito superficial de La Caverna Geda, Pinar del Río, Cuba. [Doctoral thesis. University of Pinar del Río, Cuba, and University of Alicante]., and author OJ observations).

The amphisbaenian fossil record is very scarce, due to its small elements, but also to the lack of skeletal anatomy studies (Kearney, 2002Kearney, M. (2002). Appendicular Skeleton in Amphisbaenians (Reptilia: Squamata). Copeia, 3, 719-738.). In this case, it is necessary to get a better understanding of the Cuban amphisbaenian skeleton, despite the previous studies on Cadea morphology (Zangerl, 1945Zangerl, R. (1945). Contributions to the Osteology of the Post-Cranial Skeleton of the Amphisbaenidae. The American Midland Naturalist, 33(3), 764-780.; Vanzolini, 1951Vanzolini, P. (1951). A Systematic Arrangement of the Family Amphisbaenidae (Sauria). Herpetologica, 7(3), 113-123.; Zug and Schwartz, 1958Zug, G.R., and Schwartz, A. (1958). Variation in the Species of Cadea (Amphisbaenidae), and a Record of C. blanoides from the Isla de Pinos. Herpetologica, 14(3), 176-179.; Gans and Alexander, 1962Gans, C. and Alexander, A.A. (1962). Studies on Amphisbaenids (Amphisbaenia, Reptilia). 2. On the Amphisbaenids of the Antilles. Bulletin of the Museum of Comparative Zoology, 128(3), 151-158.), in order to a better taxonomic delimitation of recent paleontological remains.

An amphisbaenian for Geda Cavern increase their fossil record, as well as their importance as Pleistocene - Holocene paleontological deposit. To date, this is the second locality in Cuba with remains of Amphisbaenian specimens, but certainly, we have a lot to explore. Amphisbaenian in Cuba have a national distribution. Amphisbaena cubana inhabits all the archipelago, even in some cays; A. barbouri occupy western Cuba, while A. carlgansi occupy eastern Cuba. The last one being restringed to Cabo Cruz peninsula. Cadea blanoides also has a national distribution, while C. palirostrata has been only found in Isla de la Juventud, at the South of the main island.

Amphisbaenians are completely fossorial, however, its appearance inside the cavern does not necessarily mean that he lived inside it. Like much of the fossil fauna found in the deposit, it may have been drawn inward from external sediments (Condis, 2010Condis, M. (2010) Inferencias paleoecológicas sobre especies de la mastofauna cuaternaria cubana, conservadas en el depósito superficial de La Caverna Geda, Pinar del Río, Cuba. [Doctoral thesis. University of Pinar del Río, Cuba, and University of Alicante].). Recent individuals have been reported from beneath limestone rocks, in lowland forest floor, near brooks, inside caves entrances, in cane fields and orchards (Henderson and Powell, 2009Henderson, R. W. and Powell, R. (2009). Natural History of West Indian Reptiles. University Press of Florida.). Also, it has been reported from caves entrances, in Santo Tomás cave, Pinar del Río Province (Zug and Schwartz, 1958Zug, G.R., and Schwartz, A. (1958). Variation in the Species of Cadea (Amphisbaenidae), and a Record of C. blanoides from the Isla de Pinos. Herpetologica, 14(3), 176-179.), close to the fossil deposit locality.

By references of others amphisbaenians of the Antilles area (Thomas & Hedges, 2006Thomas, R. and Hedges, S.B. (2006). Two new species of Amphisbaena (Reptilia: Squamata: Amphisbaenidae) from the Tiburon Peninsula of Haiti. Caribbean Journal of Science, 42(2), 208-219.), they are commonly found under rocks, logs, and accumulations of decaying plant matters, where humidity is relatively high. Their appeareance among vertebrate fossils of Geda cave deposit, indicate the presence of this taxon in the surrounding area, and supports the high humidity conditions of the karstic area.