Nactus soniae, Arnold, Nicholas & Bour, Roger, 2008

Arnold, Nicholas & Bour, Roger, 2008, A new Nactus gecko (Gekkonidae) and a new Leiolopisma skink (Scincidae) from La Réunion, Indian Ocean, based on recent fossil remains and ancient DNA sequence, Zootaxa 1705, pp. 40-50 : 41-43

publication ID	https://doi.org/ 10.5281/zenodo.180883
DOI	https://doi.org/10.5281/zenodo.6228591
persistent identifier	https://treatment.plazi.org/id/03926D37-7958-FFEF-5580-257EFCF7995E
treatment provided by	Plazi
scientific name	Nactus soniae
status	sp. nov.

Treatment

Nactus soniae n. sp.

Nactus borbonicus (nomen nudum) in Probst (1997: 144), and in Probst and Brial (2002:24).

Etymology. Named after Sonia Ribes-Beaudemoulin, present curator of the Muséum d’Histoire Naturelle, Saint-Denis, La Réunion. She organised a dozen expeditions to collect important subfossil remains of vertebrates, especially tortoises, birds and bats from the marshes of l’Ermitage near St-Gilles.

Distribution. Known only from La Réunion, southwest Indian Ocean.

Material ( Figs 2–3 View FIGURE 2 a, 2 b View FIGURE 3 ). Holotype: Grotte au Sable, St-Gilles, La Réunion; frontal bone; BMNH R16534. Paratypes: Grotte au Sable, St-Gilles, La Réunion; 1 frontal, 1 maxilla, 1 dentary; BMNH R16535-16537.

DNA sequence. Grotte au Sable, St-Gilles, La Réunion. 681 base pairs (bp) of mitochondrial DNA sequence extracted from a frontal bone, comprising 305 bp of cytochrome and 374 bp of 12S rRNA genes (J. J. Austin and E. N. Arnold, unpublished data).

Diagnosis. A small Nactus , estimated from available bones to be about 45mm from snout to vent. Frontal not elongate, with only weakly developed anterior lateral submaxillary flanges. Maxilla with dorsal lamina inset medially, so outer surface of tooth-bearing body of bone is rounded; its posterior section comparatively short. Tooth counts low with 29 teeth in maxilla and 24 in dentary of available material. Also has distinctive mitochondrial DNA sequence (12S rRNA and cytochrome b).

Differs from other Nactus in conformation of maxilla and from other Mascarene species in the following additional features: N. serpensinsula and N. durrelli of Mauritius—smaller size and lower tooth counts; N. coindemerensis of Mauritius—larger size; two undescribed subfossil species from Rodrigues (E. N. Arnold, J. J. Austin and C. G. Jones, unpublished observations)—lower tooth counts, only weakly developed anterior lateral submaxillary flanges on frontal bone, also lacking the elongation of the frontal found in one of the Rodrigues species. Distinguished from sympatric Phelsuma geckos ( Fig. 1 View FIGURE 1 ) by much narrower frontal bone with a longer tubular section, a higher dorsal lamina on the maxilla and coarser dentition.

Description. Available material is very fragmentary with only three skull elements represented. Frontal somewhat expanded anteriorly, and strongly expanded posteriorly, with an intervening narrow waist between the orbits. The tubular section of the frontal is relatively long and the sides of the expanded posterior section of the bone are thickened below. Dorsal surface slightly but distinctly concave, with a depressed anterior facet or facets that would lie under the prefrontals in a complete skull. The shape of the anterior border of the subdermal surface of the frontal, bordering this facet posteriorly is convex anteriorly with a pointed projection on each side. Small lateral flanges are visible on the frontal anteriorly which would lie under the posterior dorsal projection of the lamina of each maxilla. The three N. soniae frontals examined (including one sacrificed during DNA extraction) show considerable variation in form, including how broad they are, the shape of the anterior border of the dermal surface which is convex and pointed in the holotype but more gently rounded in the others, and the precise size of the small anterior lateral flanges. The lateral borders of the frontal anterior to its narrow waist may also be rather wavy.

Maxilla generally similar to other Nactus , especially N. serpensinsula , with a high dorsal lamina that rises to an acute point posteriorly, where it contacts the frontal, overlapping its anterior lateral flange. A row of four foramina in a horizontal line on the lateral surface of the tooth-bearing body of the bone and two more where the body and the dorsal lamina join. Differs from N. serpensinsula and other Nactus in the dorsal lamina being inset medially on the tooth-bearing body of the maxilla so, in transverse section, the outer face of this is rounded before the lamina rises. The body of the maxilla posterior to the lamina is relatively short. There are 24 teeth, a similar count to that found in Mauritian N. coindemerensis which has about 26, but considerably lower than those in N. serpensinsula and N. durrelli which have about 36–38 teeth in adults.

Dentary is similar to that of most other Nactus species, being rather slender, with a short ventral groove at the anterior extremity; six foramina in a roughly horizontal line on lateral surface which has a tridentate posterior border, medial surface with a depressed splenial scar and a V-shaped posterior border in which the upper edge has a pronounced step. The bone, which is from a relatively small individual, has 29 teeth, a count again similar to that found in Mauritian N. coindemerensis , but considerably lower than those in N. serpensinsula and N. durrelli which have about 39–40 teeth in adults.

The size of the frontals, the elements apparently from the largest individuals represented in the available sample, indicate that N. soniae was around 45mm from snout to vent. It is consequently intermediate in size between N. coindemerensis of Mauritius, which grows to about 36mm from snout to vent, and N. serpensinsula and N. durrelli from the same island which reach at least 67mm and 55mm ( Arnold and Jones, 1994).

Relationships. DNA confirms that N. soniae is a Nactus and indicates it is most closely related to the diminutive N. coindemerensis of Mauritius (J. J. Austin and E. N. Arnold, unpublished data), something also supported by its relatively small size and low tooth counts.