Ingerophrynus chrysolophus Arkhipov, Pawangkhanant, Sarker, Nguyen, Suwannapoom, Smith & Poyarkov, 2025

Ingerophrynus chrysolophus Arkhipov, Pawangkhanant, Sarker, Nguyen, Suwannapoom, Smith & Poyarkov sp. nov.

Figs 1 View Figure 1 , 2 View Figure 2 , 8 View Figure 8 , 9 View Figure 9 , 10 View Figure 10 , 11 View Figure 11 , Table 1 View Table 1

Chresonymy.

Ingerophrynus parvus View in CoL [partim] — Taylor (1962: 329–332); Ohler et al. (2002: 467); Neang and Holden (2008: 53); Chan-ard et al. (2011: 32–33); Mulcahy et al. (2018: 85–162); Srion et al. (2018: 1–7); Chan and Grismer (2019: 3); Niyomwan et al. (2019: 186–187); Zug and Mulcahy (2020: 29); Poyarkov et al. (2021: 20); Zug (2022: 15); Holden (2023: 63).

Type materials.

Holotype. • ZMMU A-8030 (field label NAP-11571), adult female from Wat Tham Sanook Temple , Tha Sae District, Chumphon Province, Thailand ( 10.481°N, 99.073°E; elevation 65 m asl.), collected on 27 January 2022, by N. A. Poyarkov, D. V. Arkhipov, P. Pawangkhanant, and C. Suwannapoom GoogleMaps .

Paratypes (n = 8). • ZMMU A-8034 , A-8039 ( two adult males; field labels NAP-11575, NAP-11580), and ZMMU A-8031 – A-8033 , A-8035 – A-8037 ( six adult females; field labels NAP-11572–11574, NAP-11576–11578) from Wat Tham Sanook Temple , Tha Sae District, Chumphon Province, Thailand ( 10.481°N, 99.073°E; elevation 65 m asl.), collected on 27 January 2022, by N. A. Poyarkov, D. V. Arkhipov, P. Pawangkhanant, and C. Suwannapoom GoogleMaps .

Referred specimens

(n = 16). • ZMMU A-8020 ( adult male; field label NAP-11165) from Pa Klok District , Phuket Province, Thailand ( 8.039°N, 98.391°E; elevation 68 m asl.), collected on 15 January 2022, by N. A. Poyarkov, D. V. Arkhipov, P. Pawangkhanant, and C. Suwannapoom GoogleMaps ; • ZMMU A-8047 – A-8060 ( 14 adult males; field labels NAP-11726–11740) and ZMMU A-8061 ( adult female; field label NAP-11741) from Khao Kra Jom , Suan Phueng District, Ratchaburi Province, Thailand ( 13.582°N, 99.178°E; elevation 998 m asl.), collected on 30 January 2022, by N. A. Poyarkov, D. V. Arkhipov, P. Pawangkhanant, and C. Suwannapoom GoogleMaps .

Diagnosis.

A member of the genus Ingerophrynus with the following combination of morphological characters: a medium-sized species ( SVL 30.3–35.7 mm in males, 34.0– 42.4 mm in females); head large and wide ( HL / HW 0.81–0.98 in males, 0.80–0.96 in females); parotoid elongate, narrow, and sharply raised; parotoid not continuous with an oblique row of conspicuously enlarged warts; warts on flanks less elevated than those of dorsum; cranial crests not thickened behind eyes; lores vertical; tympanum distinct, its diameter slightly exceeding two-thirds of eye length ( TD / ED 0.53–0.64 in males, 0.51–0.77 in females); tibia relatively short ( TIL / SVL 0.40–0.44 in males, 0.39–0.43 in females); males with a subgular vocal sac; no tarsal ridge or tibial gland; first finger longer than second; tip of third toe not reaching median subarticular tubercle of fourth toe; subarticular tubercles not enlarged; tarsal spine bases small; nuptial pads present; venter with low warts; ground color of flanks and dorsum light brown; dark brown stripes along the midline of the back; cranial ridges well-developed, bright orange.

Description of holotype

(Fig. 8 View Figure 8 ). Adult female in a good state of preservation, body stout ( SVL 42.4 mm); head relatively large, wider than long ( HL / HW 0.88); head with a pair of straight, cranial crests not thick, diverging and raised posteriorly (Fig. 8 D View Figure 8 ); snout projecting beyond lower jaw, gently rounded in lateral view (Fig. 8 C View Figure 8 ), truncated in dorsal view (Fig. 8 D View Figure 8 ); upper eyelid lacking supraciliary tubercles; protuberant nostrils at tip of snout with lateral orientation; canthus rostralis sharp, lores vertical (Fig. 8 C View Figure 8 ); tympanum distinct, approximately half diameter of eye ( TD / ED 0.51); paratoid gland elongate, rounded, low in profile, separated from eyelid by supratympanic crest (Fig. 8 D View Figure 8 ); obliquely oriented row of enlarged, round to elongate dorsolateral warts extend posteriorly from paratoid gland approximately two-thirds way down flanks (Fig. 8 A View Figure 8 ).

Forelimbs relatively long and slender ( 28.7 mm), fingers moderately long, tips blunt, not swollen; relative finger lengths: II <I <IV <III; fingers free of webbing (Fig. 8 E View Figure 8 ); finger subarticular tubercles distinct, conical; finger subarticular tubercle formula 1: 1: 2: 1; inner metacarpal tubercle slightly elongate; outer metacarpal tubercle triangular-shaped, dilated, bigger than inner metacarpal tubercle ( IMC / OMC 0.63); two metacarpal tubercles not in touch with each other (Fig. 8 E View Figure 8 ). Hindlimbs robust and short; tibia relatively short ( TIL / SVL 0.42); relative toe lengths: IV <II <I <III <IV; tips of toes like those of fingers; fourth toe nearly three times the length of third and fifth; third and fifth toes with nearly two phalanges free of web; fourth toe with four free phalanges; second toe nearly completely webbed; first toe completely webbed; webbing formula: i 1-1 ½ ii 1 ½ - 2 ½ iii 2 ½ - 3 iv 3 - 2 v; subarticular tubercles conspicuous, somewhat conical, much smaller than metatarsal tubercles, toe subarticular tubercle formula 1: 1: 2: 3: 1; inner metatarsal tubercle oval, shorter than length of first toe ( IMT / T 1 0.37); outer metatarsal tubercle smaller, rounded (Fig. 8 F View Figure 8 ).

Skin on flanks and dorsum covered with numerous conical warts, those of flanks lower in profile than those of dorsum; warts of dorsum capped by numerous spinules; enlarged series of nearly symmetrical paravertebral warts on dorsum beginning posterior to orbit and extending posteriorly beyond sacrum; venter covered with coarsely spinose granules.

Coloration.

In life (Fig. 9 A View Figure 9 ), the overall ground color of the flanks and dorsum is light brown; a prominent, symmetrical pattern of stripes running along the midline of the back extends from the tip of the snout to just above the cloaca, fading slightly posteriorly (Fig. 8 A View Figure 8 ); cranial ridges bright orange (Fig. 8 C View Figure 8 ); parotoids and posteriorly extending dorsolateral warts dark beige, ventrally countershaded with dark brown (Fig. 9 A View Figure 9 ), forming a border between the lighter brownish dorsum and dark brown flanks; dark brown crossbars on the limbs except for the brachia; the venter light brown to grayish, and ventral warts light beige (Fig. 8 B View Figure 8 ). The pupil is horizontal and black, while the iris is also black, featuring dense golden reticulations on the dorsal and ventral sides and copper reticulations medially; the pupil is edged with a thin golden line (Fig. 8 C View Figure 8 ). After preservation in ethanol for four years, all aspects of the color pattern remain; patterns of coloration of limbs and body are still visible but not as conspicuous as in life; bright orange colors on cranial crests and coloration of the iris completely faded.

Variation.

The individuals in the type series and the referred specimens are all very similar in external appearance. Individual differences in size and body proportions are presented in Table 1 View Table 1 . Males are significantly smaller than females (p <0.05): mean male body length 33.0 ± 1.3 mm ( SVL = 30.3–35.7 mm, n = 18); mean female body length 36.8 ± 2.2 mm ( SVL = 34.0– 42.4 mm; n = 10). Fig. 10 View Figure 10 displays the variation in dorsal coloration of the paratypes. There were no significant differences in the coloration of male paratypes and females, except that males had a darker throat coloration. A female specimen, ZMMU A-8031 , had a bright reddish-brown background dorsal coloration, markedly different from the duller brownish coloration of all other specimens examined (Fig. 10 View Figure 10 ). There is a certain variation in the degree of development of dark dorsal markings among the individuals: females ZMMU A-8032 , A-8035, and A-8036 had contrasting black blotches in scapular and sacral areas, while males ZMMU A-8034 and ZMMU A-8041 and female ZMMU A-8037 had almost no dark markings on the dorsum (Fig. 10 View Figure 10 ). In general, males showed duller dorsal patterns with faint borders and less contrasting dark markings.

Tadpole morphology.

A detailed description of the larval morphology of Ingerophrynus chrysolophus sp. nov. from Thailand was presented by Meewattana (2022: 30–31) (referred to as I. parvus in his work). Tadpoles of the new species have an oval-shaped head-body, 2 / 3 longer than wide; eyes with dorsal orientation; internarial distance comprising 2 / 3 of interorbital distance; spiracle sinistral; mouth-snout distance equal to snout-eye distance; vent median; tail broad with weak tail musculature; dorsal and ventral tail fins beginning at the tail base, both subequal in depth; and tail tip rounded ( Meewattana 2022). Oral disc subterminal, with ventral orientation, small papillae in mouth corner, labial tooth row formula 2 (2) / 3; beaks black with serrated edges. Tadpoles reach 20.0–25.0 mm in length; the head-body is black in dorsal and lateral aspects and translucent in ventral aspect, with intestines being visible on the posterior half of the head-body length; tail muscles blackish, tail fins transparent ( Meewattana 2022).

Osteological description.

The following description of adult skull morphology is based on the tomographic data obtained for the adult male ( ZMMU A-8059 , paratype) and the adult female ( ZMMU A-8032 , paratype) (Fig. 11 View Figure 11 ).

Cranium.

Overall, the cranium of Ingerophrynus chrysolophus sp. nov. is generally well ossified; the highly tuberculous skin appears to be quite dense optically in this species and is visible in our reconstructions, concealing parts of the skull; the densest regions at the tip of the snout and on the upper eyelidswere cut off the scans; some elements on the cranial roof show traces of hyperossification, while the otic region seems underossified; the skull shape is almost triangular in dorsal (Fig. 11 A, D View Figure 11 ) and ventral views (Fig. 11 B, E View Figure 11 ) and close to trapezoid in lateral view (Fig. 11 C, F View Figure 11 ). Snout distinctly truncate in dorsal (Fig. 11 A, D View Figure 11 ) and ventral (Fig. 11 B, E View Figure 11 ) views, not protruding beyond the upper jaw. The hyobranchial apparatus is mostly cartilaginous and thus invisible in our reconstruction; the only visible element is the well-ossified paired posteromedial process of the hyoid.

Premaxilla.

The premaxilla is a paired bone, slightly arcuate dorsally, toothless (Fig. 11 B, E View Figure 11 ). The premaxilla dorsally contributes to the internasal fontanelle ( cavum internasale), ventrally contributes to the anteromedial fenestra, and dorsomedially contacts the ventromedial part of the external nares. The alary process of the premaxilla is oriented anterodorsally. The anterior surface of the premaxillary bones is slightly granular in female and smooth in male (Fig. 11 B, E View Figure 11 ). The premaxilla contacts the maxillary bones posterolaterally and contributes to the anterior part of the nasal cavity.

Maxilla.

The paired maxilla is a toothless bone, running laterally from the nasal capsule to the level of the otic region (Fig. 11 B, E View Figure 11 ). The maxilla contacts the premaxillary anteriorly, the nasal dorsomedially, the palatine medially, the pterygoid posteromedially, and the quadratojugal posteriorly.

Nasal.

The paired nasals form the dorsal part of the snout; they contact the maxillary ventrolaterally with the well-pronounced maxillary process and the sphenethmoid posteriorly, which fills the space between the nasals and frontoparietals (Fig. 11 A, C View Figure 11 ). The nasal contributes ventrally to the nasal cavity. Dorsal surfaces of nasal bones are depressed medially and overall are slightly shagreened in male and granular in female. The paired nasals are well separated from each other, forming an internasal fontanelle medially (Fig. 11 A, D View Figure 11 ).

Frontoparietal.

The large paired frontoparietals form the roof of the skull, separated by the frontoparietal suture across their length (Fig. 11 A, D View Figure 11 ); they contact the sphenethmoid anteriorly and anteroventrally, the exooccipitals posteriorly, and the prootics posterodorsolaterally, and are fused with the latter posterolaterally. The dorsal surface of the frontoparietals is smooth in male and slightly granular in female. The dorsolateral parts of the frontoparietals form supraorbital crests all across their length and are granulated in the posterior half in male and along their entire length in female.

Septomaxilla.

The paired septomaxilla is a small bone of a complex shape located in the anterior part of the snout (Fig. 11 C, F View Figure 11 ). The septomaxilla contributes to the external nares and the anterior wall of the nasal cavity.

Vomer.

The vomer is a rather small paired bone, triradiate in shape, located in the anterior part of the palatine region, covering the cranial base between the internal nares and bearing no teeth (Fig. 11 B, E View Figure 11 ). A pair of vomers contributes to the medial and dorsal walls of the internal nares and to the ventral walls of nasal capsules.

Palatine.

The paired palatine is a rod-shaped, toothless bone with a prominent ventral ridge (Fig. 11 B, E View Figure 11 ). The palatine is located in the posterior part of the palatine region and contacts the sphenethmoid medially, the maxilla dorsolaterally, and the pterygoid posterolaterally.

Sphenethmoid.

The sphenethmoid is a single bone subcylindrical in shape, forming the anterior portion of the neurocranium (Fig. 11 B, E View Figure 11 ). It is structured like a typical cartilaginous bone with pronounced inner and outer bone layers. The sphenethmoid contacts the nasals anterodorsally, the frontoparietals posterodorsally, the palatines ventrolaterally, and the parasphenoid posteroventrally, and contributes to the nasal cavity anteriorly.

Parasphenoid.

The single parasphenoid is a large sword-shaped bone plate forming the floor of the cranium (Fig. 11 B, E View Figure 11 ). The parasphenoid contacts the sphenethmoid anteriorly, the prootics posterodorsally, the pterygoids posterolaterally, and the exoccipitals posteriorly. The parasphenoid is under-ossified laterally in the female specimen.

Squamosal.

The paired hoe-shaped squamosals are located at the side of the cranium and at a right angle to the jaw arc (Fig. 11 C, F View Figure 11 ). The squamosal contacts the prootic dorsomedially, the quadratojugal ventrally, and approaches the pterygoid medially. The squamosal is densely tuberculous dorsally, with the otic ramus forming the supratympanic crest on its dorsolateral surface (Fig. 11 A, D View Figure 11 ). The medial part of the otic ramus appears to be underossified in the female specimen. Ventral and zygomatic rami are well developed, ossified, and smooth.

Pterygoid.

The paired pterygoids are triradiate in shape, with each having three branches (rami; Fig. 11 C, F View Figure 11 ). The processus oticum (medial ramus) is directed dorsomedially, with a prominent excavation in the posterior view, contacting the prootic. The processus palatinum (anterior ramus) is directed anteriorly, with a prominent lateral ridge, and contacts the maxilla laterally and the palatine anteriorly (Fig. 11 B, E View Figure 11 ). The processus quadratum (posterior ramus) of the pterygoid is directed posteriorly, contacting the quadratojugal.

Quadratojugal.

The paired quadratojugals are rather small bones, located posterolaterally on the skull (Fig. 11 B, E View Figure 11 ). The quadratojugal contacts the maxilla anteriorly, the squamosal dorsally, approaching the pterygoid posteromedially, and articulating with the angulosplenial bone of the lower jaw posteroventrally.

Prootic.

The prootic is an incompletely ossified paired bone, seemingly spongious, largely cartilaginous posteriorly (Fig. 11 B, E View Figure 11 ). The posterolateral part of the dorsal surface of the prootic bears an excavation. The prootic contacts the squamosal dorsolaterally, the pterygoid ventrolaterally, the parasphenoid ventrally, and the frontoparietal dorsomedially and is fused with the latter anteromedially. The prootics largely contribute to the otic capsules.

Stapes.

The paired stapes (columella) are largely mineralized, slightly arched, and extending medially (Fig. 11 C, F View Figure 11 ). The stapes is oriented laterally and slightly anteriorly and comes close to the prootics, to the area of the oval window.

Saccular otoconia.

The otic capsule is partially filled with calcium carbonate in the form of the saccular otoconia. The paired saccular otoconia are well mineralized, subspherical in shape, and located deep inside the inner ear.

Exoccipital.

The paired exoccipital is the posteriormost bone of the skull, forming occipital condyles and the foramen magnum (Fig. 11 B, E View Figure 11 ). The two exoccipitals slightly touch each other posterodorsally and posteroventrally. The exoccipitals show traces of underossification laterally, in the otic region. The exoccipital contacts the frontoparietal anterodorsally, the parasphenoid anteroventrally, and contributes anterolaterally to the otic capsule.

Mandible.

The lower jaw is shaped like a solid bony arch and comprises three bone elements, namely, paired angulosplenials, dentaries, and mentomeckelians, the latter two being completely fused (Fig. 11 C, F View Figure 11 ). The space between dentaries and angulosplenials is likely filled with Meckel’s cartilage, invisible in our reconstructions.

Etymology.

The species name “ сhrysolophus ” is a Latinized adjective in the nominative singular, masculine gender, derived from the Ancient Greek words “ χρυσός ” or “ chrysos, ” meaning “ gold, ” and “ λόφος ” or “ lophos, ” meaning “ crest ” or “ ridge. ” The species name is given in reference to the characteristic golden-orange coloration of supratympanic crests in the new species. We suggest the following common names for the new species: Golden-crested Dwarf Toad (in English), Khang kok khrae hua tong (คางคกแคระห ั วทอง, in Thai), and Zlatogrebnistaya shlemonosnaya zhaba (Златогребнистая шлемоносная жаба, in Russian).

Comparisons.

Ingerophrynus chrysolophus sp. nov. can be distinguished from I. biporcatus , I. celebensis , I. claviger , I. divergens , I. galeatus , I. ledongensis , I. macrotis , I. philippinicus , I. quadriporcatus , and I. wangyingyongi by having small body size ( SVL 30–36 mm in males, 34–42 mm in females vs. 55–70 mm in males, 60–80 mm in females of I. biporcatus ; up to 130 mm of I. celebensis ; 33 mm in male, 58–69 mm in females of I. claviger ; 28–45 mm in males, 50–55 in females of I. divergens ; up to 50 mm in males, 80 mm in females of I. galeatus ; 47–55 in males, 62–64 mm in females of I. ledongensis ; up to 50 mm in males, 55 mm in females of I. macrotis ; 52–78 mm in males, 58–86 mm in females of I. philippinicus ; 48–50 mm in males, 49–62 in females of I. quadriporcatus ; and 44.8–53.3 mm in males, 54.3–57.9 mm in females of I. wangyingyongi ). Ingerophrynus сhrysolophus sp. nov. further differs from I. biporcatus , I. divergens , I. galeatus , I. ledongensis , I. quadriporcatus , and I. wangyingyongi by having parotoid not continuous with an oblique row of conspicuously enlarged warts (vs. continuous). Ingerophrynus сhrysolophus sp. nov. can be further distinguished from I. claviger and I. philippinicus by having cranial crests not thickened behind eyes (vs. cranial crests distinctly thickened immediately behind the eye level). Ingerophrynus сhrysolophus sp. nov. further differs from I. kumquat by having nuptial pads present (vs. absent) and by having first finger longer than second (vs. second finger longer than first).

Finally, Ingerophrynus сhrysolophus sp. nov. superficially most closely resembles its sister species I. parvus s. str.; however, the new species can be readily distinguished from the latter by having the following suite of morphological characters: smaller body size in both sexes ( SVL 30.3–35.7 mm [avg. 33.0 mm] in males, 34.0– 42.4 mm [avg. 36.8 mm] in females vs. 33.1–36.7 mm [avg. 34.8 mm] in males, 44.5–48.5 mm [avg. 47.0 mm] in females); slightly higher HL / HW ratio in both sexes (0.81–0.98 [avg. 0.90] in males, 0.80–0.96 [avg. 0.87] in females vs. 0.83–0.89 [avg. 0.85] in males, 0.78–0.87 [avg. 0.83] in females); higher ratio TD / ED in males (0.53–0.64 [avg. 0.58] vs. 0.44–0.51 [avg. 0.48]), but lower in females (0.51–0.77 [avg. 0.60] vs. 0.53–0.81 [avg. 0.68]); lower ratio TIL / SVL in females (0.39–0.43 [avg. 0.41] vs. 0.44–0.45 [avg. 0.45]); lower ratio IMT / T 1 in both sexes (0.33–0.42 [avg. 0.38] in males; 0.31–0.40 [avg. 0.37] in females vs. 0.35–0.51 [avg. 0.42] in males, 0.35–0.51 [avg. 0.42] in females), and by the presence of bright orange coloration of the cranial crests (vs. brown).

Advertisement call.

The male advertisement call of Ingerophrynus chrysolophus sp. nov. is described in detail in the Results section (see above); the call parameters are presented in Suppl. material 1: table S 5; the waveform and the sonogram of the male advertisement call of the new species are presented in Fig. 6 B View Figure 6 . The male advertisement call of the new species differs from the call of I. parvus s. str. by a lower peak frequency ( 1,292 –1,378 Hz vs. 2,438 –2,625 Hz), fewer short (0.02– 0.05s vs. 0.05– 0.07s) calls in the series (8–10 vs. 13–15), and by having fewer pulses in the call (5–6 vs. 6–9).

Distribution.

Ingerophrynus chrysolophus sp. nov. is reliably known from central, eastern, western, and southern Thailand ( Mae Hong Son, Tak, Kamphaeng Phet, Uthai Thani, Kanchanaburi, Ratchaburi, Phetchaburi, Prachuap Khiri Khan, Chumpon, Ranong, Surat Thani, Phang Nga, Phuket, Krabi, Nakhon Si Thamarat, Trang, Songkhla, Satun, Trat, and Chanthaburi provinces); the adjacent parts of southern Myanmar ( Tanintharyi Region and Yangon State); and southwest Cambodia (Cardamom Mountains) (Fig. 1 View Figure 1 ). According to the results of the species distribution modeling (Fig. 7 B View Figure 7 ), the occurrence of the new species is expected in the northernmost Peninsular Malaysia ( Perlis State); further studies are required to clarify the extent of its distribution in the Thai-Malay Peninsula.

Natural history notes.

All individuals of the new species were collected during the night from swampy areas along the slow-moving, shallow stream within a closed-canopy evergreen montane or lowland tropical forest. Breeding and larval development take place in rain pools or side pools along the stream banks, typically with sandy or silty bottoms and numerous dead leaves and other plants accumulated on the bottom ( Meewattana 2022). In Thailand, the new species occurs in various habitats, from undisturbed montane tropical forests to heavily disturbed bamboo forests and rubber plantations. In Suang Phueng ( Ratchaburi Province), the new species was recorded in syntopy with three other bufonid species: Ansonia karen Suwannapoom, Grismer, Pawangkhanant, Naiduangchan, Yushchenko, Arkhipov, Wilkinson & Poyarkov, 2021 ; Phrynoidis asper (Gravenhorst, 1829) ; and Duttaphrynus cf. melanostictus (Schneider, 1799) .

Conservation status.

At present, the new species is known from multiple locations across southern, central, western, and eastern Thailand, southern Myanmar, and southwest Cambodia (Fig. 7 B View Figure 7 ). The potential threats to this species are habitat loss and degradation due to intensified logging and deforestation. We propose the new species to be classified as Least Concern ( LC) according to the IUCN’s Red List categories ( IUCN 2019).