Megophrys (Xenophrys) megacephala Mahony, Sengupta, Kamei & Biju, 2011

Mahony, Stephen, Kamei, Rachunliu G., Teeling, Emma C. & Biju, S. D., 2020, Taxonomic review of the Asian Horned Frogs (Amphibia: Megophrys Kuhl & Van Hasselt) of Northeast India and Bangladesh previously misidentified as M. parva (Boulenger), with descriptions of three new species, Journal of Natural History 54 (1 - 4), pp. 119-194 : 154-157

Megophrys (Xenophrys) megacephala Mahony, Sengupta, Kamei & Biju, 2011

Megophrys megacephala Mahony, Sengupta, Kamei & Biju, 2011, p. 37 , In: A new low altitude species of Megophrys Kuhl and van Hasselt ( Amphibia : Megophryidae ), from Assam, Northeast India. Zootaxa, 3059, 36 – 46.

Holotype. Adult male ( ZSI A 11213 [field tag SDBDU 2009.681]), from Basistha Road, approximately 5 km south of Basistha temple (26°03 ′ 59 ″ N, 91°47 ′ 32 ″ E, 145 m asl.), Ri Bhoi district [originally stated as East Khasi Hills — see Remarks section], northern Meghalaya state, India, collected by RGK on 14 July 2009 ( Mahony et al. 2011; Kharkongor et al. 2018).

Paratypes. Adult male ( ZSI A 11214 [field tag SDBDU 2009.697 ]), collected from the type locality by RGK on 15 July 2009; three adult males ( ZSI A 11321 – 11323 [field tags A0014, A0015, A0472), a subadult male ( ZSI A 11324 [field tag A0528]) and an adult female ( ZSI A 11326 [field tag A0196]), from ‘ Garbhanga Reserve Forest (25°55 ′ – 26°06 ′ N, 91°36 ′ – 91° 47 ′ E), Kamrup district, Guwahati, Assam, India ’, collected in May 2002, July 2003, April 2004, and June 2005 ( Mahony et al. 2011) .

Originally referred specimens. Adult male ( SDBDU 2009.698 ), collected along with holotype; adult male ( ZSI A 11325 [field tag A0100]), from ‘ Mayeng Hill Reserve Forest (25°49 ′ – 25°55 ′ N, 91°21 ′ – 91°29 ′ E), Kamrup district, Assam, India ’, collected on 23 June 2003 ( Mahony et al. 2011) .

Newly referred specimens. Adult female ( SDBDU 2007.281 ) and subadult female ( SDBDU 2007.282 [ Figure 9 (a,b)]) from a stream tributary of the Ganol River (25.553055, 90.293333, 675 m asl.), near Missimagre village , Tura municipality, West Garo Hills district , Meghalaya state, NEI, collected by SDB and RGK on 7 October 2007; adult female ( BMNH [18]72.4.17A [ Figure 9 (c,d)]) from “ Sikkim ” [in error] state, NEI, collected by T .C. Jerdon ca. 1870.

Updated comparison. Megophrys megacephala (adult males, N = 7; adult females, N = 3; subadult female, N = 1; juvenile male, N = 1) differs from the following species that have not yet been assigned to a subgenus or species group through molecular analyses: from M. damrei by shorter hind limbs, SHL / SVL 41.0 – 49.0% and FOL / SVL 34.0 – 45.3%, N = 12 (vs. SHL / SVL 50.5 – - 50.7% and FOL / SVL 48.0%, N = 2), and longer head, HL/ SVL 39.7 – 43.7%, N = 12 (vs. HL/ SVL 36.9 – 38.7%, N = 2) (Mahony 2011); from M. shuichengensis by much smaller adult size,male SVL 45.9 – 53.4 mm, female SVL 49.3 – 64.4 mm (vs. adult male SVL 102.0 – 118.3 mm, N = 8, adult female SVL 99.8 – 115.6 mm, N = 7 [ Tian et al. 2000]); from M. feii by larger adult size, male SVL 45.9 – 53.4 mm, female SVL 49.3 – 64.4 mm (vs. adult male SVL 24.3 – 25.1 mm, N = 4, adult female SVL 28.2 – 28.9 mm, N = 2), and lateral dermal fringes on toes absent (vs. present), and nuptial pads on fingers of males present (vs. absent) ( Yang et al. 2018).

Megophrys megacephala differs from M. parva s.s. by significantly larger adult size, male SVL 45.9 – 53.4 mm, female SVL 49.3 – 64.4 mm (vs. male SVL 33.9 – 36.0 mm, N = 2, female SVL 41.1 – 41.4 mm, N = 2), larger head width relative to SVL, HW / SVL 40.2 – 45.1%, N = 12 (vs. HW / SVL 32.1 – 33.9%, N = 4).

Megophrys megacephala differs from currently named members of the M. (X.) megacephala SG based on the following combinations of characters: from M. ancrae by larger male adult size, SVL 45.9 – 53.4 mm (vs. adult male SVL 39.1 – 45.0 mm, N = 8), larger head width relative to SVL, HW / SVL 40.2 – 45.1%, N = 12 (vs. HW / SVL 30.4 – 35.8, N = 10), and finger length formula, IV <II <I < III (vs. I <II <IV < III).

Refer to the relevant sections for morphological comparison between this species and remaining M. (X.) megacephala SG taxa.

Suggested common name. Big Headed Indian Horned Frog ( Mahony et al. 2011), since this species attains proportionately the largest head relative to body size of all Indian Megophrys species.

Distribution. Based on a revised distribution provided herein (see Remarks section below) Megophrys megacephala is currently known from two disjunct populations, an eastern and western ( Figure 2 ). The eastern population is from Ri Bhoi district of Meghalaya state and the adjoining southern Kamrup district of Assam state between 90 and 145 m asl. In Assam, it has been collected from Garbhanga R.F. (Reserve Forest) and Mayeng Hill R.F. ( Choudhury et al. 2001; Mahony et al. 2011). The western population, reported herein for the first time, is from Tura municipality in the West Garo Hills district of Meghalaya state where this species was collected from 675 m asl. (and might be found up to 875 m asl. [ Sangma and Saikia 2015] — see Remarks section below), which is ~ 120 km southwest of the nearest previously known population. It is expected that this species may be found in intervening low to midelevation areas where enough suitable habitat remains.

Habitat and natural history. Refer to Mahony et al. (2011) for details relating to the type series and originally referred specimens. The newly referred specimens from Tura municipality were collected at around 18:00 h during light rains alongside a rocky, low gradient, 2 m wide shallow stream flowing through a disturbed forested area. The historically collected adult female specimen (BMNH [18]72.4.17A) contained moderately well developed pigmentless ova demonstrating that females of this species reach sexual maturity at around 50 mm SVL.

Remarks. For holotype description, variation, secondary sexual characters, etymology, habitat preference and natural history notes refer to Mahony et al. (2011), and Table 2. The type locality was originally erroneously stated to be located in the ‘ East Khasi Hills [district] ’ ( Mahony et al. 2011), corrected to Ri Bhoi district by Kharkongor et al. (2018).

The two additional specimens from the West Garo Hills district of Meghalaya hereby assigned to this species based on morphological and molecular similarity significantly increases the geographical and elevational distribution of this species to potentially include most of southern and western Meghalaya state. An additional specimen that is morphologically assignable to this species (BMNH [18]72.4.17A [ Figure 9 (c,d)) collected by Jerdon, is given the locality ‘ Sikkim ’. Many of Jerdon ’ s collection localities are considered unreliable since he did not make field notes ( Günther 1875; Biju et al. 2016; Giri et al. 2019; Mahony et al. 2018). Since this species has not since been collected from north of the Brahmaputra River, it is more likely that Jerdon collected this specimen during his travels in Meghalaya state. Therefore, unless proven otherwise, Sikkim state should not be considered part of the geographic distribution for this species. Newly assigned referred specimens do not significantly differ in morphological aspects from the type series, though adult females are comparably smaller (SVL 49.3 – 49.9 mm, N = 2) than the female paratype (SVL 64.4 mm).

Choudhury et al. (2001) provided some field observations for this species as Megophrys parva based on six specimens collected from 90 to 110 m asl from Garbhanga R.F. and Mayeng Hill R.F in southern Kamrup district, Assam. Sengupta et al. (2010) reported two species from the Rani – Garbhanga area (as Xenophrys parva and X. sp. 1), with no further information; based on the locality proximity, one or both species may be referable to M. megacephala . Sangma and Saikia (2015) reported Megophrys (Panophrys) boettgeri (as Xenophrys boettgeri , and as X. boetgerri [sic]) from ‘ Tura Peak (N 25°30 ′ 18.2 ″ & E 90°14 ′ 35.1 ″) at an elevation of 834 m ’. The figure ( Sangma and Saikia 2015, pl. 3a) depicts a species morphologically most similar to either M. megacephala or M. serchhipii , both of which are reported from the vicinity of Tura for the first time in the present study. Based on the SVL provided (75 mm), Sangma and Saikia ’ s (2015) specimen most likely represents a female M. megacephala . Mahony et al. (2013) reviewed previous reports of Megophrys boettgeri from NEI and considered that all reports of this species were either misidentifications of other species, or insufficient information (such as lack of identifiable voucher specimens, images, or morphological descriptions) was provided to identify the species being reported. Kharkongor et al. (2018), referring to Sangma and Saikia (2015), proposed to again include Megophrys (Panophrys) boettgeri on the Indian checklist, but recognised the need to further investigate the identity of the specimen from Sangma and Saikia (2015). Both M. megacephala and M. serchhipii are currently the only known Megophrys species from Meghalaya that typically lack dorsolateral ridges on the body (though some individuals of M. serchhipii have short dorsolateral ridges anteriorly), a character shared with M. boettgeri and many other Megophrys species found elsewhere. Apart from this very superficial similarity, M. megacephala and M. serchhipii differ considerably from M. boettgeri s.s. in almost all morphometric proportions and consequently these species should not be confused taxonomically. Megophrys boettgeri is therefore not a member of the Indian fauna. Purkayastha (2018) included M. parva in a checklist of amphibians from Guwahati city, Assam (which borders Garbhanga R.F.) and provided a photograph of a specimen that is indistinguishable from M. megacephala . Specimens in the ZSI reported from Rongrengiri, Garo Hills as ‘ Megophrys monticola Kuhl & V. Hass. ’ ( Pillai and Chanda 1981) and as M. parva ( Chanda 1994) should be compared with M. megacephala .

Megophrys megacephala has consistently been resolved as the sister taxon to all remaining members of the M. (X.) megacephala SG ( Figures 1, S1 – S 3 ; Mahony et al. 2017, figs. 1 & 3; Mahony et al. 2018, fig. 4), with results from molecular dating analyses suggesting that this species split from the most recent common ancestor of the M. (X.) megacephala SG at ca. 8.3 MY.

Figures

Figure 1. ML phylogenetic tree of the subgenus Megophrys (Xenophrys) based on the concatenated mt +nuDNA alignment. Bootstrap values ≥95% are represented by a black spot; 80–95% represented by a grey spot; <80% not given. Numbers next to species names correspond with specimen numbers in Table 1.

Figure 2. Topographic distribution map of the Megophrys (X.) megacephala SG taxa: Left. All taxa from Northeast India and surrounding countries: diamonds represent type localities; circles represent referred localities based on examined specimens; circles with central dot represent identifications based on literature where sufficient evidence was available (see Remarks sections); Right. Inset rectangle enlarged to show the distributions of species from more densely sampled southern Nagaland and northern Manipur states, Northeast India. Blue lines represent major rivers; grey lines represent international borders.

Figure 3. Megophrys parva adult male paralectotype (BMNH 1947.2.25.12: SVL 33.9 mm) in preservation, from Kayin state, Myanmar: (a). dorsal view; (b). ventral view; (c). profile view of head; (d). ventral view of hand; (e). ventral view of foot.

Figure 9. Megophrys megacephala referred specimens from Meghalaya state, India: (a–b). subadult female (SDBDU 2007.282: SVL 49.3 mm) in life from West Garo Hills district: (a). dorsolateral view; (b). ventral view; (c–d). adult female (BMNH [18]72.4.17A: SVL 49.9 mm) in preservation from unknown locality: (c). dorsal view; (d). ventral view.