Sirenoscincus mobydick, Miralles & Anjeriniaina & Hipsley & Müller & Glaw & Vences, 2012

Miralles, Aurélien, Anjeriniaina, Mirana, Hipsley, Christy A., Müller, Johannes, Glaw, Frank & Vences, Miguel, 2012, Variations on a bauplan: description of a new Malagasy “ mermaid skink ” with flipper-like forelimbs only (Scincidae, Sirenoscincus Sakata & Hikida, 2003), Zoosystema 34 (4), pp. 701-719 : 704-708

Sirenoscincus mobydick n. sp.

( Figs 1 A-D; 2-5)

HOLOTYPE. — Northwest Madagascar, Sofia region , commune rurale of Port Bergé II, 3 km from the village of Marosely, plateau of Bongolava (15°38’49.7’’S, 47°34’59’’E), 250 m above sea level, 14-15.XI.2004, collected by Mirana Anjeriniaina,UADBAR70487 (field number MA293 = ZCMV 12920 ).

PARATYPE. — Same data as holotype, UADBA R70488 (field number MA283).

DISTRIBUTION AND NATURAL HISTORY. — The species is only known from the type locality of the Bongolava plateau, although a Sirenoscincus record from Belambo forest near Antsohihy ( Raselimanana 2008), north of the type locality of Sirenoscincus mobydick n. sp., could also refer to this species. Both known specimens were captured with pitfall traps and drift fences over night, on sandy soils within the deciduous dry forest covering the plateau. This suggests that Sirenoscincus mobydick n. sp. may likely have arenicolous and fossorial habits like species of the genus Voeltzkowia Boettger, 1893 or Paracontias minimus (Mocquard, 1906) , taxa with whom it shares several highly derived morphological characteristics probably linked to a fossorial lifestyle in sandy habitat (e.g., rudimentary eye sunken below cephalic scales, external ear opening extremely reduced, shovel-shaped snout with a countersunk lower jaw). Compared to S. yamagishii , S. mobydick n. sp. presents a higher degree of reduction of the cephalic scalation as absence of frontonasal (likely fused with the frontal), absence of preocular (likely fused with the loreal), and absence of postsubocular (likely fused with the pretemporal). These traits, together with a higher degree of forelimb regression, congruently suggest that it is morphologically more strongly adapted to fossoriality than S. yamagishii .

ETYMOLOGY. — The specific epithet refers to Moby Dick, the famous albino sperm whale imagined by Herman Melville (1851), with whom the new species shares several uncommon characteristics, such as the lack of hindlimbs, the presence of flipper-like forelimbs, highly reduced eyes, and the complete absence of pigmentation (see Fig. 7 ). The name is an invariable noun in apposition.

DIAGNOSIS. — The new species is a member of the genus Sirenoscincus as defined by Sakata & Hikida (2003a), easily distinguished from all other genera of skinks worldwide by the combination of: 1) the presence of two forelimbs and the absence of hindlimbs (all other genera except Jarujinia being either quadrupedal, completely legless, or having two hindlimbs only); 2) the regressed eyes sunken below scales; and 3) completely depigmented skin. It is differentiated from S. yamagishii (see Figs 1 ; 6 ), the only other species described within the genus, by several apomorphic characteristics: 1) the flipper-like aspect of the forelimbs (versus presence of four stout claws in S. yamagishii ); 2) the absence of frontonasal, likely fused with the frontal (versus presence of both scales); 3) the absence of preocular, likely fused with the loreal (versus presence of both scales); and 4) the absence of postsubocular, likely fused with the pretemporal (versus presence of both scales). Additionally, S. mobydick n. sp. has one presacral vertebra less than S. yamagishii (52 in the new species versus 53), but this difference may not be reliable given the rather small sample size involved.

DESCRIPTION OF THE HOLOTYPE

External morphology

In a relatively good state of preservation, except for the tail which has been autotomised 42.3 mm posterior to the cloaca, and the presence of a constriction of the body posterior to the forelimbs where the collection tag has been tied ( Fig. 1 ). Unsexed, apparently adult specimen. Snout-vent length 70.5 mm, width at midbody 4.1 mm, head width at level of parietal scale 3.6 mm, forelimb length 2 mm.

In general, an elongated and slender, small-sized and uniformly pale skink with two reduced flipperlike forelimbs and no hindlimbs. Snout rounded in dorsal view, bluntly wedge-shaped in lateral view; rostral extends posteriorly both dorsally and ventrally; paired supranasals contacting medially; frontonasal absent; prefrontals absent; frontal large, hourglassshaped, approximately as wide as long; frontoparietals absent; interparietal triangular, contacting frontal; parietals meet posterior to interparietal; nuchals undifferentiated, occupying the equivalent of two rows of dorsal cycloid scales, two on the left side, three on the right side; nostril between rostral and apex of nasal; nasal wedge-shaped; loreal single, rectangular, approximately two times longer than high; preocular absent, probably fused with the loreal; presubocular and postsubocular absent; supraocular single; ocular single, small, roughly pentagonal; eye sunken deeply below ocular, supraocular and the third supralabial; primary temporal single; secondary temporals two; tertiary temporals two; supralabials five, the second the smallest, the third the highest, partly overlapping the ocular region; postsupralabials one; external ear opening minute, covered by two scales significantly smaller than the adjacent ones. Upper jaw distinctly projecting lower jaw; mental wider than long; postmental wider than long; infralabials four, first only in contact with postmental; three pairs of large chin scales, members of first and second pair separated by one scale row, members of third pair separated by three scale rows ( Fig. 2 ). Longitudinal scale rows at midbody 20; paravertebral scales 94 (including nuchals), similar in size to adjacent scales; ventral scales 98 (including postmental); inner preanal scales overlap outer. Two rounded flipper-like forelimbs, very short, slightly flattened, without any visible digit or claw ( Fig. 2D ); no hindlimbs.

Colouration

Several years after fixation, the entire head, body and tail pale overall. The eyes are recognisable as dark spots. In life, the colouration was likely uniformly pinkish like in Sirenoscincus yamagishii , due to the blood vascularisation of the skin (see Figs 1 ; 2 ).

Skeletal features ( Figs 3-5 )

Due to the methodology of X-ray CT, only the ossified parts can be described:

Pectoral girdle. Relatively complete and well developed, dorso-ventrally flattened and roughly rhomboidal. Clavicles strongly curved (S-shaped), flattened dorso-ventrally, with a wide and rounded proximal extremity, a narrow and pointed distal extremity,and a process at their mid-length posteriorly directed. Interclavicle cruciform, with a rounded anterior process approximately as long as the lateral processes these having narrow and pointed distal ends, and a rounded posterior process about 1.5 times longer. Suprascapulae roughly triangular, more ossified medially than laterally.Scapula, coracoid and precoracoid not separated from each other, forming a continuous scapulocoracoid bone. Pericoracoid extremely regressed, fragmented into several poorly ossified residues: two strips separating the sternum from the coracoid, and two pairs of small rodlike structures, posteriorly barely contacting with the cranial extremities of the precoracoid and the coracoid, respectively, and anteriorly converging toward the anterior part of the interclavicle. Coracoid foramen oval, almost open into the anterior coracoid fenestra. Anterior (=primary) coracoid fenestra not completely closed, the pericoracoid being too reduced to delimitate its anterior margin. Posterior (= secondary) coracoid fenestra located in the anterior part of the coracoid; its margins are not clearly delimited from the surrounding osseous tissue (for this reason, the posterior coracoid fenestra may also be interpreted as a very thin and poorly ossified fossa rather than a true fenestra). Pentagonal sternum poorly ossified, as long as wide, as wide as the interclavicle, more ossified posteriorly than anteriorly, pierced by a large, round and median sternal fontanelle in its posterior part, and laterally connected to two pairs of sternal ribs.Xiphisternum “Y-shaped”, with three elongated rodlike processes: a median process connecting the posteriormost extremity of the sternum and two posterolaterally directed processes connecting a single pair of xiphisternal ribs.

Forelimbs. Small but relatively well developed, with the exception of the autopodial bones, these being significantly reduced in size and number. Humerus relatively elongated, articulating with the scapula through a relatively well-developed glenoid fossa, and with enlarged proximal and distal ends twisted in relation to one another at an angle of approximately 90°.Ulna and radius relatively reduced in comparison to the humerus, as representing approximately only half of its length. Carpals including three globular elements: the largest (most likely the ulnar carpal), spherical and proximal, and the two smaller probably representing distal carpals (possibly IV and V). Metacarpals possibly represented by two elongated elements (possibly III and IV).No phalangeal bones.

Pelvic girdle. Highly reduced; composed of two separate, curved and rodlike hemipelves. Pubis, ischium and ilium not clearly separated from each other. Pubis and ischium apparently fused to form the anteroventral projection of each hemipelvis, distally compressed and curved, forming a trifurcated anterior cranial end; ilium forming an elongated cigar-shaped dorso-caudal projection.

Pelvic bony corpuscles. Hindlimbs absent, with the notable exception of two faintly distinguishable bony corpuscles probably representing rudiments of ancestral hindlimb bones, posterior to – and not in contact with – the pelvic girdle, floating freely below the cloacal vent. Less likely, these corpuscles may be interpreted as hemibacula (or hemibaubella), calcified structures present in the hemipenes (or hemiclitores) of several distinct groups of squamates, although they could be expected to occur deeper in the tail root, closer to the retractor muscle of the inverted hemipenis.

Additional features

52 presacral vertebrae.Sclerotic rings formed by five ossicles, the upper being the smallest in size ( Fig. 5 ). Osteoderms present within each scale, with the exception of the first two pairs of supralabials, the nasals, the first three pairs of infralabials, the mental, the auricular scales covering the ear-openings, and the ocular scales covering the eyes.Rostral scale only ossified on its dorsal side. Osteoderms present in the parietals, interparietal and frontal scales hardly distinguishable from the underlying skull bones, to which their central part seems to be fused, only the edges being clearly distinct ( Fig. 3 ).

Variation

External morphological examination reveals that the paratype (UADBA R70488) shares all the diagnostic characters previously mentioned for the holotype: absence of frontonasal, absence of preoculars and postsuboculars, and 20 rows of scales around mid-body. Its colouration in preservative and its size (snout-vent length = 66.7 mm) are almost identical to those described for the holotype.

Figures

FIG. 1. — Sirenoscincus Sakata & Hikida, 2003: A-D, S. mobydick n. sp., preserved holotype UADBA R70487, lateral view of the entire specimen (A), lateral (B) and ventral (C) views of the anterior body part, showing highly reduced flipper-like forelimbs, and close-up of the forelimb (D); the constriction of the body posterior to the forelimbs is an artefact of the fastening of the collection label; E-G, living specimen of S. yamagishii Sakata & Hikida, 2003 from Ankarafantsika, Madagascar, lateral view of the anterior body part (E), dorsolateral view of the entire specimen (F), and close-up of the right forelimb with four claws (G). Scale bars: 1 mm (not shown for S. yamagishii because unavailable). (Photographs E-G: Falk S. Eckhardt.)

FIG. 7. — Illustration from an early edition of Moby-Dick. Public domain picture drawn by A. Burnham Shute (1892).

FIG. 6. — A, B, drawings of the lateral and dorsal views of the holotype of Sirenoscincus yamagishii Sakata & Hikida, 2003 (holotype specimen KUZ R50922); C, D, the only northern species of Voeltzkowia Boettger, 1893, V. mira Boettger, 1893 (ZSM 867/0); E, F, one member of the southern group,V.lineata (Mocquard,1901) (ZSM 1624/2010 = ZCMV 12845).A and B have been redrawn after Sakata & Hikida (2003a). E is symmetrically reversed, thus representing the right side. Scale bars: 1 mm (not shown for A and B because not indicated in the original figure).

FIG. 2.— Drawings of the holotype of Sirenoscincus mobydick n. sp.(UADBA R70487): A-C, dorsal (A), ventral (B) and lateral (C) views of the head;D, close-up of the arm (picture symmetrically reversed,thus representing the right forelimb).The colouration in life has been presently inferred from both the preserved specimen and the supposedly identical living colouration of S.yamagishii. Scale bars:1 mm.

FIG. 3. — Computed tomographic reconstruction of the anterior body part of the holotype specimen of Sirenoscincus mobydick n. sp. (UADBA R70487) in dorsal (A, C) and lateral views (B, D). The osteodermic “chain mail” is represented in red in A and B, and digitally removed from C and D. Scale bars: 0.5 mm.

FIG. 4. — Computed tomographic reconstruction of the pectoral girdle and forelimbs of the holotype specimen of Sirenoscincus mobydick n. sp.(UADBA R70487) in lateral (A) and dorsal (B) views;pectoral girdle in lateral (C) and dorsal (D) views.Scale bar: 1 mm.

FIG. 5. — Computed tomographic reconstruction of the skull of the holotype specimen Sirenoscincus mobydick n. sp.(UADBA R70487) with the sclerotic rings coloured in green,in lateral (A) and dorsal (C) views.B represents the ossicles in the sclerotic ring,redrawn from A.