Rhombophryne serratopalpebrosa ( Guibé, 1975 ), Guibe, 1975

Scherz, Mark D., Ruthensteiner, Bernhard, Vences, Miguel & Glaw, Frank, 2014, A new microhylid frog, genus Rhombophryne, from northeastern Madagascar, and a re-description of R. serratopalpebrosa using micro-computed tomography, Zootaxa 3860 (6), pp. 547-560 : 550-554

Rhombophryne serratopalpebrosa ( Guibé, 1975)

( Figs. 2–3 )

Remark. This species was originally described by Guibé (1975) as Mantipus serratopalpebrosus . This description was reiterated verbatim by Guibé (1978). It was then re-described as Plethodontohyla serratopalpebrosa based on the holotype by Blommers-Schlösser & Blanc (1991), and then again briefly in Vences & Glaw (2003), and was transferred to Rhombophryne by Glaw & Vences (2007).

Holotype. MNHN 1975.24, an adult female containing ca. 14 oocytes (as confirmed by soft-tissue micro-CT scan) collected in the scrub at the summit of Marojejy [“dans les fourrés au sommet du Marojézy”] by Charles P. Blanc, 29 November 1972 according to Guibé (1975). The principle peak of the Marojejy massif is at 2132 m above sea level ( Goodman 2000). However, according to the catalogue of the Paris museum, the holotype was collected at Massif du Marojezy (1400 m) dans les fourres (Vences & Glaw 2003), indicating substantial uncertainty about the actual altitude of the type locality.

Diagnosis. A microhylid frog assigned to the genus Rhombophryne on the basis of its lack of enlarged finger discs (vs. presence in several Plethodontohyla species), and morphological similarity to R. coronata and R. vaventy sp. nov., which have been assigned to Rhombophryne on the basis of genetic data (see below). Currently, no diagnostic characters are known in external or internal morphology for the distinction of these two genera ( Andreone et al. 2005; Wollenberg et al. 2008; Glaw et al. 2010).

This species is distinguished from all other Rhombophryne species and also all Plethodontohyla species by the possession of the combination of the following characters: rather small size (female SVL 28 mm), granular dorsal skin, smooth ventral skin, fingers and toes without enlarged terminal discs, second and fourth fingers almost equal in size, fifth toe of nearly equal length to third toe, tibia 47% of SVL, prevomers and vomerine teeth straight, nearly meeting medially, four (the posterior-most indistinct) evenly-spaced superciliary spines, a strong, almost straight supratympanic fold extending forward to the supraocular region, tympanum 78% of eye diameter, the absence of dorsolateral folds, flanks and thighs brownish with yellow spots, domed columellar footplates ( Fig. 2 e), and nasals with an anterior and posterior lateral process.

Within the genus Rhombophryne , R. serratopalpebrosa may be distinguished from its congeners by the following characters: from R. mangabensis by larger size (28 mm SVL vs. 20–24 mm), and presence of four superciliary spines (vs. absence); from R. alluaudi by its smaller size (28 mm vs. 40–60 mm), and presence of four superciliary spines (vs. absence); from R. testudo by smaller size (28 mm vs. 33–45 mm), absence of barbels on the lower lip (vs. presence), and presence of four superciliary spines (vs. absence); from R. coudreaui by the absence of webbing between digits (vs. traces of webbing), and presence of four superciliary spines (vs. absence); from R. guentherpetersi by absence of porous glandular formation in the latero-dorsal region (vs. presence), and presence of four superciliary spines (vs. absence); from R. laevipes by smaller size (28 mm vs. 45–47 mm), granular dorsal skin (vs. smooth), and presence of four superciliary spines (vs. absence); from R. minuta by larger size (28 mm vs. 16–22 mm), and presence of four superciliary spines (vs. absence); from R. matavy by smaller size (28 mm vs. 39–49 mm), and presence of four superciliary spines (vs. absence); and from R. coronata by slightly larger size (28 mm vs. 21–23 mm), presence of a strong, almost straight supratympanic fold extending to the supraocular region (vs. indistinct supratympanic fold), larger relative tympanum size (TDH/ED 78% vs. 59%), and longer relative tibia length (TIBL/SVL 47% vs. 39–41%). For distinction from R. vaventy sp. nov., see its diagnosis below.

Additionally, due to the morphological similarity of Plethodontohyla to Rhombophryne we provide differentiation between R. serratopalpebrosa and all of the nominal Plethodontohyla species: R. serratopalpebrosa may be distinguished from all Plethodontohyla species by the presence of superciliary spines (vs. absence). Additionally, it may be distinguished from P. notosticta , P. guentheri , P. mihanika , and P. inguinalis by the lack of enlarged terminal discs on its digits (vs. presence) and the lack of a sharp border between the dorsal and lateral colouration (vs. presence); from P. t uberata by smaller size (28 mm vs. 35–45 mm), and lack of dark dorsal markings (vs. presence); from P. ocellata by absence of large black spots bordered with white in the inguinal region (vs. presence); from P. bipunctata by absence of dark circular spots in the inguinal region (vs. presence); and from P. brevipes by smaller size (28 mm vs. 36 mm).

Redescription of the holotype. A specimen in a poor state of preservation. The ventral dermis has been cut open, probably to study character states of the shoulder girdle, and the left lateral region has been cut open, probably to check the sex.

Body robust. Head wider than long. Snout rounded in dorsal view and truncated in lateral view. Canthus rostralis slightly concave. Loreal region weakly concave, with an anterior fold projecting in an S-shape above the nostril. Nostrils not protuberant, directed laterally, equidistant between eye and tip of snout; eye-nostril distance smaller than the internarial distance. Tympanum distinct; oval in shape, width 78% of eye diameter (¾ according to Blommers-Schlösser & Blanc 1991). A series of four, evenly spaced superciliary spines present above each eye, the posterior-most of which is indistinct and was not noted in any previous description ( Guibé 1975, 1978; Blommers-Schlösser & Blanc 1991; Vences & Glaw 2003), and the anterior three of which are distinct. Supratympanic fold strong, almost straight, extending forward to the supraocular region. Vomerine teeth present in two long straight series, almost meeting at the median line. Tongue not notched, but in poor condition.

Arms slender. Fingers without webbing, relative lengths 1<2≤4<3 (2 and 4 are very similar in size, and were described by Guibé [1975, 1978] as being equal in size); without trace of finger-tip enlargement; nuptial pads absent; prepollex not externally visible; inner metacarpal tubercle indistinct; outer metacarpal tubercle indiscernible, although described by Guibé (1975, 1978) as ‘peu marqués’ (weakly evident)—this may be obscured due to the staining of the specimen (see Colouration of the Holotype). Hindlimbs slender; tibiotarsal articulation of the right leg reaches the snout tip, while the left tibiotarsal articulation reaches between the tympanum and the eye. This difference may be due to the bent profile of the specimen, and the incision made on the left side, or the fracture in the left femur, as both legs are equal in length. Nonetheless, which of these tibiotarsal articulations reflects the natural level of articulation is unclear, and this character does not, therefore, feature in the diagnosis above (Note: this feature was described as reaching the snout tip by Guibé 1975, 1978, but as reaching the eye in Blommers-Schlösser & Blanc 1991, Vences & Glaw 2003, and Glaw & Vences 2007). Inner metatarsal tubercle indistinct, outer metatarsal tubercle absent; no webbing between toes; relative toe lengths 1<2<5≤3<4 (5 and 3 are very similar in size, and were described by Guibé [1975, 1978] and Blommers-Schlösser & Blanc [1991] as being equal in size). Dorsal skin finely granular, however described by Guibé (1975, 1978) as ‘roughly granular’; texture presumably lost as a consequence of preservation. Dorsolateral folds absent. According to Guibé (1975, 1978), a medio-dorsal fold was present from the tip of the snout to the vent, but this appears to be an artificial character, probably due to strong fixation. Ventral skin completely smooth.

Measurements: The holotype measurements (in mm) are: SVL 28.5, HW 12.8, HL 8.6, ED 3.2, END 2.3, NSD 2.4, NND 3.6, TDH 2.5, TDV 2.0, HAL 9.5, FORL 20.3, HIL 50.5, FOL 15.8, FOTL 24.3, TIBL 13.3, IMCL 1.1, IMTL 1.4.

Osteology of the holotype ( Figs. 2 , 3 and Supplementary Fig. S1): Skull triangular in dorsal view. Prevomer divided; post-choanal portion long and straight, extending anteroventrolaterally from the sphenethmoid where it nearly meets medially; postchoanal prevomers overlapping, fused with, or replacing the palatine, possessing a serrated ridge along the ventral surface that is here referred to as being ‘vomerine teeth’, although the true dental nature of these teeth is uncertain. Teeth present on maxilla and premaxilla. Premaxilla L-shaped in anterior view, U-shaped in dorsal view; a thick lateral ramus and tapering, pointed medial ramus extend posteriorly from the anterior bone plate. Septomaxilla U-shaped in dorsal view, consisting of a flat anterior plate with one posteriorjutting ramus on its ventromedial edge, and one on its ventrolateral edge; the lateral ramus possesses one medial and one lateral apophysis; the medial apophysis extending medioventrally, almost to the level of the medial ramus in dorsal view. Squamosal broad and Y-shaped. Nasal broad and fairly elliptical, with two lateral projections from its lateral edge, the posterior of which is much longer than the anterior. Columella slender with a slightly domed footplate, reminiscent of a red blood cell ( Fig. 2 e).

Humerus with just one humeral crista (crista ventralis), beginning 15% from the proximal end of the humerus, and extending to its midpoint. Caput humeri with a distinct, knob-like postero-dorsal apophysis on its distal edge, and a ventral ridge in line with the humeral crista, but not as high (46% of crista ventralis height). Ulna and radius fused. Finger phalangeal formula: 2,2,3,3. Terminal phalanges of fingers 2 and 3 with distal knobs. Prepollex present but small (28% of first metacarpal). Clavicles slim and curved anteriorly, approximately in parallel to the anterior curve of the coracoid. Sternal features not apparent from the scan, and probably not ossified.

The left femur has been fractured 33% of the length from its distal end. Toe phalangeal formula: 2,2,3,4,3. Terminal phalanges of toes 2, 3, 4, and 5 with distal knobs. Ilia long, extending beyond the sacrum, nearly to the level of the transverse processes of the seventh presacral vertebra; ilial shafts almost cylindrical, with a subtle dorsal crest extending most of their length; posteriorly fused synostotically with the ischia and pubes, which are ossified. Ten vertebrae are present: the atlas, three thoracic vertebrae (T), four lumbar vertebrae (L), the sacrum and the urostyle. Urostyle with a dorsal ridge running along its anterior half. Transverse process breadths relative to the breadth of the sacral processes are T1 (99.7%), T2 (116.8%), T3 (94.1%), L1 (72.9%), L2 (68.3%), L3 (69.1%), and L4 (73.0%). Posterior articular processes round.

Colouration of the holotype: The specimen has been dyed a bright green, possibly in an attempt to stain it for an unknown reason with an unknown chemical. Unfortunately, this dye has obscured any of the original colour. However, the original description ( Guibé 1975) includes the following comments on body colour (translated from the original French): “dorsally brown, with fine black vermiculated dots, somewhat lighter on the dorsal surface of the head. The flanks and thighs are dorsally and posteriorly tobacco-brown in colour, riddled with yellow spots. This colour runs into the dorsal pattern in the inguinal region. Tibia and tarsus dorsally coloured as the back. Ventrally, many fine dark spots on the throat and chest, more loosely obvious on the abdomen and thighs, with small white spots anteriorly, wider posteriorly.”

Figures

FIGURE 2. Comparative osteology of Rhombophryne vaventy sp. nov. (ZSM 357 / 2005, left in all pairs), and Rhombophryne serratopalpebrosa (MNHN 1975.24, right in all pairs), scaled to be equal in size; see Supplementary Figure S 1 for manipulable model and scale. a: spinal columns in dorsal view (A = Atlas, T = Thoracic Vertebra, L = Lumbar Vertebra, S = Sacrum, U = Urostyle); b: ilia in dorsal view, with arrows indicating the third lumbar vertebrae and anterior-most end of the ilia; c: hands in ventral view, with arrows indicating the prepollex; d: head in ventral view, with arrows indicating the postchoanal prevomerine palate; e: columellae in dorsal view.

FIGURE 3. Comparative skull osteology of Rhombophryne serratopalpebrosa (MNHN 1975.24, right in all pairs) and Rhombophryne vaventy sp. nov. (ZSM 357 / 2005, left in all pairs), scaled to be equal in size. a: lateral view; b: ventral view; c: dorsal view. Abbreviations: angspl = angulosplenial, col = columella, fpar = frontoparietal, max = maxillary, mmk = mentomeckelian bone, pmax = premaxilla, pro = prootic, prsph = parasphenoid, pter = pterygoid, pvom = prevomer, pvom / neopl = prevomer / neopalatine (either fused or replaced), qj = quadratojugal, spheth = sphenethmoid, spmax = septomaxilla, sq = squamosal.