Rhombophryne proportionalis, Scherz & Hutter & Rakotoarison & Riemann & Rödel & Ndriantsoa & Glos & Roberts & Crottini & Vences & Glaw, 2019

Scherz, Mark D., Hutter, Carl R., Rakotoarison, Andolalao, Riemann, Jana C., Rödel, Mark-Oliver, Ndriantsoa, Serge H., Glos, Julian, Roberts, Sam Hyde, Crottini, Angelica, Vences, Miguel & Glaw, Frank, 2019, Morphological and ecological convergence at the lower size limit for vertebrates highlighted by five new miniaturised microhylid frog species from three different Madagascan genera, PLoS ONE 213314, pp. 1-45 : 28-33

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https://doi.org/ 10.1371/journal.pone.0213314

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Rhombophryne proportionalis

sp. nov.

Rhombophryne proportionalis sp. nov.


( Figs 1 View Fig 1 , 2 View Fig 2 , 3 View Fig 3 , 5 View Fig 5 , 10 View Fig 10 and 11 View Fig 11 , Tables 1 and 2 View Table 2 )

Remark. This species was previously referred to as Stumpffia sp. Ca34 [ 15, 46] and as Stumpffia sp. 39 MV-2012 ( KC351481 View Materials ) [ 20].

Holotype. ZSM 1826 View Materials /2010 ( ZCMV 12404 , GenBank accession number KC351380 View Materials and KU 937808 View Materials for 5’ and 3’ fragments of the 16S rRNA gene, respectively, and KF611640 View Materials for the cox1 gene), an adult male specimen (seen calling, not recorded) collected at Bepia Campsite on the Tsaratanana massif (Camp 3; 14.1182˚S, 48.9782˚E, 2294 m a.s.l.), Diana Region, former Antsiranana province, northern Madagascar on 16 June 2010 by M. Vences, D.R. Vieites, R.D. Randrianiaina, S. Rasamison, and E. Rajeriarison.

Paratypes. ZSM 1840 View Materials /2010 ( ZCMV 12405 , GenBank accession number KC351481 View Materials and MK 459317 View Materials for 5’ and 3’ fragments of the 16S rRNA gene, respectively), adult male specimen with the same collection data as the holotype; and ZSM 636 View Materials /2014 ( DRV 6224 ), an adult presumed male specimen collected at Andranomadio Campsite in Tsaratanana (Camp 4; 14.0801˚S, 48.9854˚E, 2503 m a.s.l.) on 16 June 2010 by the same collectors .

Diagnosis. A diminutive frog assigned to the genus Rhombophryne on the basis of absence of clavicles, presence of vomerine, maxillary, and premaxillary teeth, short and broad skull, and genetic affinities. It is separated by uncorrected p-distances of 7.0–12.9% in the analysed 3’ fragment of the 16S rRNA gene from other members of the genus Rhombophryne .

Rhombophryne proportionalis sp. nov. is characterised by the unique combination of the following characters (n = 3 male specimens): (1) male SVL 11.0– 12.3 mm; (2) ED/HL 0.40–0.48; (3) HW/SVL 0.33–0.37; (4) FARL/SVL 0.33–0.35; (5) TIBL/SVL 0.34–0.36; (6) HIL/SVL 0.21– 1.32; (7) finger 1 reduced, 2 and 4 short; (8) toe 1 highly reduced, 2 somewhat reduced; (9) maxillary and premaxillary teeth present; (10) vomerine teeth present; (11) lateral colour bor- der absent; (12) black inguinal spots sometimes present; (13) postchoanal vomer present, spatulate, medially fused to parasphenoid; (14) nasal broad and not laterally displaced; (15) quadratojugal-maxilla contact strong and broad; (16) zygomatic ramus of squamosal long, thick, curved, and horizontal; (17) clavicles absent; (18) prepollex short and triangular; (19) carpal 2 present; (20) finger phalangeal formula 2-2-3-3; (21) toe phalangeal formula 2-2-3-4- 3; (22) unpulsed calls emitted in series of 9–17 calls at irregular intervals; (23) non-frequency modulated calls; (24) call dominant frequency 5460 ± 117 Hz (n = 79); (25) call duration

45.4 ± 8.2 ms (n = 79); (26) inter-call interval 63.0 ± 9.0 ms (n = 73).

Among extremely miniaturized cophylines, this species is unique in possessing vomerine teeth. It can be distinguished from almost all other miniaturised species in lacking clavicles (also absent in S. contumelia, S. obscoena, S. davidattenboroughi, S. makira, S. achillei, and S. analanjirofo, and some specimens of S. tridactyla, unpublished data). It is also characterised by a dark colouration of the lateral surface of the head with a distinct colour border, and less reduced fingers and toes. Confusion with juvenile Rhombophryne species is still possible, but these have much larger teeth proportional to their skull size, and most lack the distinct lateral

head colouration and possess clavicles. The call is unique among the frogs of Madagascar and is instantly distinctive in being emitted as a rapid, high-pitched series of tonal notes.

Holotype description. Specimen in a good state of preservation, part of the right thigh removed as a tissue sample. Body somewhat rhomboid; head wider than long, narrower than body; snout rounded in dorsal view, squared in lateral view; nostrils directed laterally, not protuberant, closer to eye than to tip of snout; canthus rostralis rounded, concave; loreal region flat, vertical; tympanum indistinct, round, about 57% of eye diameter; supratympanic fold distinct, weakly raised, curving slightly from posterior corner of eye over tympanum toward axilla; tongue very broad, disc-like, posteriorly free, unlobed; maxillary teeth present; vomerine teeth present in two tiny patches either side of the midline; choanae rounded. Forelimbs slen- der; subarticular tubercles faint, single; outer metacarpal tubercle faint, paired; inner metacarpal tubercle distinct, elongated; hand without webbing; first finger reduced, second and fourth short; relative length of fingers 1 <2 = 4 <3; finger tips not expanded. Hind limbs robust; TIBL 34% of SVL; lateral metatarsalia strongly connected; inner metatarsal tubercle thin and indistinct; outer metatarsal tubercle small and indistinct; no webbing between toes; first toe highly reduced, second toe short; relative length of toes 1 <2 <5 <3 <4; fifth toe distinctly shorter than third. Skin on dorsum smooth in preservative, without distinct dorsolateral folds. In life, the dorsal skin was smooth was scattered tubercles, and distinct ridges above the scapular region ( Fig 10 View Fig 10 ). Ventral skin smooth in preservative, granular in life.

After eight years in 70% ethanol, the dorsum is chocolate brown in colour, darker over the head, with a faint dark brown line running from the inguinal region anteriorly toward the eye. The dorsal leg has a dark brown crossband on the shank. The lateral head has a distinct colour border to the dorsum, being a much darker brown, its border defined by the supratympanic fold. The flank has an indistinct colour border to the venter. The venter is brown with cream flecks, slightly darker and less flecked on the chin. The ventral legs and arms are as the ventral abdomen in colour. The bottom of the foot is dark brown along the medial half. Colour in life as in preservative but more vibrant.

Variation. For measurements, see Table 1. The paratypes are in general very similar to the holotype in morphology. ZSM 636/2014 is slightly smaller than the other specimens, and has a slightly shorter, more rounded head. Its supratympanic fold is also less curved than those of the other specimens, being rather more straight from the eye to above the arm. ZSM 1840/ 2010 has a more massive body than the others. The colouration of the specimens is relatively consistent, with the whole venter of ZSM 1840/2010 being darker than those of the other two specimens. The dorsolateral lines of the holotype are present in ZSM 1840/2010, but not in ZSM 636/2014, instead being broken in that specimen into spots above the suprascapular region and lines in the inguinal region. The crossbands of the shanks are less distinct in ZSM 1840/2010 than the other two specimens.

Bioacoustics. Specimens called only during the day, from open, shrubby landscape between dense vegetation, on the ground. In some areas, numerous specimens could be heard calling in a chorus. Calls were recorded from an uncollected specimen by M. Vences ( Fig 5C View Fig 5 , Table 2 View Table 2 ) at around 11h40 on 15 June 2010 in Camp Bepia (14.11822˚S, 048.97822˚E, 2294 m a.s.l.), and further calls were heard but not recorded at Camp Andranomadio (14.0801˚S, 048.9854˚E, 2503 m a.s.l.). A precise description of the call structure is difficult; the vocalization is a series of short tonal units that cannot readily be assigned to units. In past studies, we have described roughly comparable structures differently: in Stumpffia psologlossa, where the units have a very short duration, as a single call composed of pulses [ 14], in Rhombophryne mangabensis as a series of notes [ 52], and in R. minuta two closely spaced units were seen as components of a single note [ 52]. To allow comparison within Rhombophryne we here define the tonal units in the vocalizations of the new species as notes, and the entire series as a call, but emphasize that it also would be possible to define each unit as call and the entire series as call series, or to consider each unit as a pulse as their duration falls within the 5–50 ms range for which the pulse category was recommended by Köhler et al. [ 33].

Calls are rapid series of high-pitched slightly frequency modulated notes. Each call consists of a series of 9–17 notes, and calls are repeated at long and irregular intervals. For detailed call parameters, see Table 2 View Table 2 .

Osteology ( Fig 11 View Fig 11 ). Based on ZSM 1826/2010 (figured) and ZSM 636/2014 (not figured).

Cranium ( Fig 11 View Fig 11 C–11F). Shape and proportions. Skull short and stout, relatively wide, widest at quadratojugal anterior to the otic region. Short rostrum. Braincase broad.

Neurocranium. Well ossified except the weakly calcified otic capsules. Sphenethmoid well ossified, in contact with the frontoparietal in ZSM 1826/2010 but not in ZSM 636/2014, with a calcified anterior medial cone; broadly separated from prootic. Prootic in dorsal contact with lateral flange of frontoparietal, ventral contact with parasphenoid alae, not approaching contralateral. Septomaxilla miniscule, roughly spiralled, similar in shape to those of other Rhombophryne (see [ 25]). Columella (stapes) well ossified, pars media plectra (stylus) steeply sloping upwards proximally to its broad, bilobed, flattened pars interna plectra (baseplate). Nasal broad, curved over the nasal capsule, triangular, acuminate maxillary process not closely approaching maxillary pars facialis, broadly separated from contralateral, situated anterior to frontoparietal. Frontoparietal with slanted anterior edge, laterally bulging, with short lateral flange covering prootic, posteriorly weakly connected to exoccipital, anteroventrally contacting sphenethmoid, lacking any dorsal process (suggestions of such processes in ZSM 1826/ 2010).

Parasphenoid with broad, squared cultriform process and broad perpendicular alae, shorter than frontoparietals, posteromedial process not participating in foramen magnum, anteroventrally in contact with postchoanal vomer and not in contact with neopalatine. Vomer divided into pre- and postchoanal portions; prechoanal portion narrow, arcuate, triradiate, with a short lateral and anterior ramus and long posterior ramus; postchoanal portion spatulate bearing a single vomerine tooth or a pair thereof, separated from contralateral by a narrow space, in dorsal contact with the parasphenoid proximally and the neopalatine distally, lacking an anterior projection. Neopalatine laminar, broader than lateral postchoanal portion of vomer, laterally approaching but not contacting the maxilla, exceeding the lateral-most point of the postchoanal vomer to approach the anterior tip of the parasphenoid but not in contact with it, such that the vomer contacts the neopalatine near its midpoint and not at its terminus.

Maxillary arcade quite robust, maxilla and premaxilla bearing numerous diminutive teeth, premaxilla and maxilla in narrow contact anteriorly. Premaxilla with a broad acuminate dorsal alary process rising vertically, pars palatina shallowly divided into a narrow palatine process and broad lateral process. Maxilla with a low triangular pars facialis and a narrow pars palatina, its posterior tip acuminate and broadly overlapping the quadratojugal, the lingual surface of the pars palatina in broad contact with the anterior ramus of the pterygoid.

Pterygoid with a short medial ramus, long anterior ramus with broad contact with the maxilla, leaving a channel for the pterygoid cartilage, posterior ramus broad and posterolaterally calcified to the quadratojugal complex. Quadratojugal bowed laterally, broadly connected to the ventral ramus of the squamosal, and with a broad articular surface with the maxilla, bearing a large posteroventral knob. Squamosal with a broadened ventral ramus and narrow otic and zygomatic rami, the otic ramus long and thin and oriented dorsally, the zygomatic ramus short and thin, oriented anteriorly.

Mandible slim and edentate, largely unremarkable, with a low coronoid process on the angulosplenial. Mentomeckelians strongly connected to the dentary, with unusual, flat ventrolateral projections.

Posteromedial processes of hyoid proximally pointed with a broad medial crista.

Postcranial skeleton ( Fig 11A, 11B, 11G and 11H View Fig 11 ). Eight procoelous unfused presacrals, much broader than long, lacking neural spines, with round posterior articular processes, presacral I with a mostly complete neural arch, presacrals II–IV with thicker and longer transverse processes than V–VIII. Sacrum with expanded diapophyses, the leading and trailing edges roughly equally angled, the articulation type IIB sensu Emerson [ 42]. Urostyle bicondylar, long, broadening posteriorly, without lateral processes and with a low dorsal ridge.

Pectoral girdle without ossified prezonal or postzonal elements, lacking ossified clavicles. Coracoid broad, strongly flared with a large medial articular surface with the contralateral. Scapula also robust, with a broad pars acromialis distinct from the pars glenoidalis. Cleithrum ossified for half the width of the scapular border, acuminate, thickened anteriorly. Suprascapula unossified.

Humerus with a well-developed crista ventralis and no medial or lateral cristae. Radioulna broad with a distinct sulcus intermedius. Carpals well ossified in ZSM 1826/2010 and poorly ossified in ZSM 636/2014, composed of radiale, ulnare, prepollical element, element Y, carpal 2, and large post-axial element formed by carpals 3–5. Finger phalangeal formula is standard (2-2-3-3). Small distal knobs on terminal phalanges of the fingers. A very small prepollex is present in ZSM 1826/2010 but is not visible in ZSM 636/2014.

Pubis partly calcified, iliac shafts passing ventral to and beyond sacrum, nearly cylindrical, without a dorsal crest and with a weak dorsal prominence and shallow oblique groove. Femur weakly sigmoid with a low posterior crest. Tibiofibula shorter than femur, with a sulcus intermedius. Tibiale and fibulare weakly fused proximally and distally. T1 and T2+3 tarsals present, T1 considerably smaller than T2+3. Centrale present but not large. Prehallux unossified. Phalangeal formula standard (2-2-3-4-3).

Distribution, natural history, and conservation status. Rhombophryne proportionalis sp. nov. is known from two localities (Bepia and Andranomadio) on the Tsaratanana massif in northern Madagascar. Both of these sites fall within the Tsaratanana National Park (formerly a Strict Nature Reserve). It is a terrestrial species that lives among the leaf litter. Two other cophyline frogs, Platypelis alticola and P. tsaratananaensis, are also known from these locations, and both are currently listed as Endangered, due to their small distribution <2000 km 2, presence in a single threat-defined location, and potentially on-going decline in habitat quality. We therefore suggest R. proportionalis sp. nov. also to be Endangered, following the same rationale.

Etymology. The species epithet is the Latin adjective proportionalis meaning ‘proportional’, in reference to the comparatively proportional dwarfism that this species has apparently undergone (see discussion). It is a feminine adjective in the nominative singular.


Biodiversity Institute, University of Kansas


National Museum of Kenya













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