Leiolopisma ceciliae, 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 : 43-45

Leiolopisma ceciliae n. sp.

Etymology. Named after Cécile Mourer-Chauviré, celebrated specialist on fossil birds, who took part in excavations for subfossil remains on La Réunion between 1987 to 2001, identifying half a dozen of new species of birds. She also proposed the hypothesis of a ‘great extinction’ on the island, associated with cataclysmic volcanic eruptions, 180,000–230,000 years ago ( Mourer-Chauviré et al., 1999).

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

Material ( Figs 4–6 ). Holotype: Grotte au Sable, St-Gilles, La Réunion; right dentary; BMNH R16538. Paratypes: Grotte au Sable, St-Gilles, La Réunion; 1 juvenile frontal, 1 fused postorbital and postfrontal, 2 right maxillae*, 2 quadrates*, 1 left pterygoid, 4 left and 5 right dentaries*, 2 right posterior mandibles*, 6 presacral vertebrae*, 3 left and 3 right humeri*, 1 sacrum, 2 left and 3 right pelves*, 1 left and 1 right femora*, 1 right tibia; BMNH R16539-16564. Grottes des Premiers Français, St-Paul, La Réunion; 1 right quadrate, 1 right posterior mandible, 1 right humerus; BMNH 16565-16567. Cave near St-Paul, La Réunion; 1 right dentary, 1 partial right humerus, 1 right tibia; BMNH 1977.881-883 (material previously reported and tibia illustrated by Arnold, 1980).

Most paratype material of Leiolopisma ceciliae is deposited in the reptile collection of the Department of Palaeontology, Natural History Museum, London. An asterisk indicates that examples of the elements concerned have also been placed in the Muséum d’Histoire Naturelle, St-Denis, La Réunion.

DNA sequence. Grotte au Sable, St-Gilles, La Réunion. 683 bp of mitochondrial DNA sequence extracted from a left dentary, comprising 307 bp of cytochrome b and 376 bp of 12S rRNA genes ( Austin and Arnold, 2006—GenBank accession numbers: AY 818748 , AY 818818 ).

Diagnosis. A Leiolopisma intermediate in adult size and robustness between the two Mauritian species of the genus, L. telfairii and the giant L. mauritiana . Most similar to L. telfairii but differs in larger maximum size, coarser dentition, frontal bone narrower anteriorly at least in young animals, the fused postorbital and postfrontal bones with shorter posterior section and less prominent lateral spur, and quadrate more expanded lateromedially. L. mauritiana grows much larger than L. ceciliae and has coarser dentition. L. ceciliae is also separated from L. telfairii and L. mauritiana by distinctive mitochondrial DNA sequence (12S rRNA and cytochrome b gene fragments).

Fossil remains distinguished from those of the sympatric skink Gongylomorphus bojerii borbonicus by larger size, fused frontal bones and absence of a Meckel’s groove in the dentary.

Description. Available material is fragmentary, but seven cranial and six postcranial elements are represented. Comparison with material of living L.telfairii indicates a maximum snout-vent length of at least 175mm. Frontal bones fused from an early stage of development as in other lygosomine skinks, narrower anteriorly than in L. telfairii at least in young animals. Fused postfrontal and postorbital bones with a shorter posterior section than in L. telfairii and with a less prominent lateral spur that is less obviously directed forwards. Dentaries with a closed Meckel’s groove and sometimes more robust than in equivalent sized L. telfairii from mainland of Mauritius (described by Arnold, 1980), but less so than in L. mauritiana ; about six foramina in a horizontal line on anterior lateral surface. Dentition of maxillae and dentary bones coarser than in equivalent-sized L. telfairii and finer than in L. mauritiana : this is reflected in differences in tooth number for animals of similar size ( Fig. 7 ) and in robustness of the teeth. Quadrate more expanded lateromedially than in L. telfairii and tibia with a more prominent lower tubercle.

Distinctive features of type. Robust dentary originally with 25 teeth (numbers 2,3,4,9,14 and 22 missing), the last three teeth decreasing in size; a roughly horizontal line of six foramina present on the anterior lateral surface of the bone.

DNA sequence. DNA of L. ceciliae differs from equivalent regions of the genome of living L. telfairii from Round island, north of Mauritius, in 39 nucleotide substitutions (5.7% of uncorrected divergence), and from L. mauritiana by 29 nucleotide substitutions (4.2% uncorrected divergence) – Austin and Arnold (2006).

Relationships. A phylogeny of 42 species of skinks based on mitochondrial DNA associates L. ceciliae with the other two species of Leiolopisma , corroborating the clade status of this genus ( Austin and Arnold, 2006). DNA sequence confirms that Leiolopisma is part of the Lygosominae , something also supported by its fused frontal bones, and within this subfamily belongs to the Eugongylus group of genera. It also indicates that, of the two Mauritian species in the genus, L. ceciliae may be more closely related to the giant L. mauritiana , rather than to the morphologically more similar L. telfairii ( Austin and Arnold, 2006) .

Figures

FIGURE 4. Leiolopisma ceciliae n. sp., material from Grotte au Sable, St-Gilles, La Réunion. Holotype. Dentary (lateral and medial views). Scale in mm.

FIGURE 5. Leiolopisma ceciliae n. sp., material from Grotte au Sable, St-Gilles, La Réunion. Selected paratypes, from individuals of various sizes. Top row: left mandible (lateral view), right maxilla (lateral view), fused left postfrontal and postorbital bone (dorsal view), left quadrate (posterior view). Middle row: right dentary (medial view), posterior left mandible (lateral view). Bottom row: Left humerus, left pelvis (lateral view), sacrum (dorsal view), presacral vertebrae (lateral and ventral views), right femur, tibia. Scale in mm.

FIGURE 6. Leiolopisma ceciliae n. sp., material from Grotte au Sable, St-Gilles, La Réunion. Paratype. Frontal of juvenile animal (ventral and dorsal views, anterior upwards). Scale in mm.

FIGURE 7. Variation in number of teeth with size of maxillae (above) and dentary bones (below) in different species of the Mascarene skink genus Leiolopisma. Stars: L. ceciliae n. sp. from La Réunion. Assemblage to left: L. telfairii from Mauritius (triangles: living animals from Round Island, dots: subfossil material from mainland of Mauritius). Assemblage to right: subfossil L. mauritiana from mainland of Mauritius. Some symbols indicate more than one specimen.