Taxonomic status of Coryphophylax maximiliani Fitzinger in: Steindachner, 1867 with notes on Coryphophylax subcristatus (Blyth, “1860” 1861)

Morphology

The study was based on 20 museum specimens (14 of the Nicobar population and 6 of C. subcristatus, and no live individuals were captured or collected for this study. Meristic data was taken with a Mitutoyo™ dial calliper to the nearest 0.1 mm. Morphological data were recorded with an Olympus stereo binocular microscope SZ40. The following morphological characters were recorded following Sadasivan et al. (2018) and Ambekar, Murthy & Mirza (2020) with slight modifications. The following measurements were taken: snout-vent length (SVL, from tip of snout to anterior border of cloaca), head length (HL, from snout tip to posterior border of tympanum), head width (HW, distance from left to right outer edge of the head at its widest point), head height (HH, dorsoventral distance from top of head to underside of jaw at transverse plane intersecting angle of jaws), snout-eye length (SE, from snout tip to anterior border of orbit), eye to tympanum (ET, from posterior border of orbit to anterior border of tympanum), jaw length (JL, from rostrum to corner of jaw), interorbital width (IO, transverse distance between anterodorsal corners of left and right orbits), nares to eye (NE, distance from the anterior edge of orbit to posterior edge of naris), snout width/internasal distance (IN, transverse distance between left and right nares), tympanum diameter (TD, greatest diameter of tympanum), orbit diameter (OD, distance between anterior and posterior margins of orbit), lower arm length (LAL, distance from elbow to distal end of wrist, or just underside of forefoot when the limb is flexed), upper arm length (UAL, distance from anterior insertion of forelimb to elbow when the limb is flexed), crus length (CL, length of crus (tibia) from knee to heel), hind foot length (HFL, distance from proximal end (heel) of hind foot to distal most point of fourth toe), trunk length (TrL, from forelimb insertion to hind limb insertion), trunk height (TrH, depth midway between the fore and hind limb insertions), trunk width (TrW, width midway between the fore and hind limb insertions), tail length (TaL, from posterior border of cloacal opening to tip of tail), tail height (TaH) and tail width (TaW, at tail base). Meristic characters were counted for multiple individuals per species. The following characters were scored: mid-body scale rows (MBS, number of scale rows around the trunk at midbody), mid-dorsal scales (MD, counted from the first erect dorsal crest spine to the level above the vent), ventral scales (VEN, number of scales from below mental around the base of the dewlap to anterior border of cloaca), fourth toe lamellae (LAM4, number of 4^th toe lamellae, from 1^st lamella at the digit’s cleft to the most distal lamella), supralabials (SL, posterior end defined by the last enlarged scale that contacts the infralabials at the corner of mouth), infralabials (IL, posterior end defined by the posterior-most enlarged scales that contact the supralabials at the corner of the mouth), ventral scales on the belly (VENB, number of scales posterior to the dewlap to the anterior border of cloaca). Multivariate principal component analysis (PCA) was performed on selected morphometric values: HL, HH, HW, TrL, LAL and CL (Table S2). The variables were selected for the analysis as data for them was complete. These values were corrected for SVL and were later log-transformed.

Molecular methods

Molecular data for the gene 16S rRNA generated by Krishnan (2005) were downloaded from GenBank, and accession numbers and their collection localities are listed in Table 1. Gonocephalus pyrius was chosen as an outgroup for the phylogenetic analysis. The downloaded sequences were aligned in Mega X (Kumar et al., 2018) using CLUSTALW (Thompson, Higgins & Gibson, 1994) with default settings. Sequences that did not align were excluded from the dataset. The aligned dataset was analysed in a maximum likelihood (ML) framework on the IQ-TREE online portal (Trifinopoulos et al., 2016). The optimum sequence evolution model was determined through ModelFinder (Kalyaanamoorthy et al., 2017) based on AIC values. The analysis was run with an ultra-fast tree search method (Hoang et al., 2018) with 1,000 pseudo-replicates to assess branch support. The resulting tree was visualised and edited with FigTree (Rambaut, 2012). Uncorrected p-distances were calculated using Mega X with default settings, and the partial deletion option was chosen to deal with missing data.

Molecular analysis

The ML phylogeny was based on 446 bp of mitochondrial 16S rRNA and was rooted with Gonocephalus pyrius Harvey, Rech, Riyanto, Kurniawan & Smith, 2021 (Fig. 1, Table 1). The sequence substitution model selected was TPM2u+F+G4. The analysis recovered two clades, clade I, comprising C. brevicauda, clade II comprises a basal Coryphophylax sp. (Coryphophylax sp. 1 Fig. 1) from Car Nicobar Island (the northernmost island in the Nicobar Islands), which is sister to a sub-clade containing representatives from Nicobar Islands (Coryphophylax maximiliani) and Coryphophylax subcristatus sensu stricto (ML bootstrap support 90%). The monophyly of Coryphophylax maximiliani + Coryphophylax subcristatus sensu stricto received low bootstrap support (56%).

Morphology and nomenclature: The PCA plot shows the separation of the Nicobar Island population from C. subcristatus and C. brevicauda, where PC1 + PC2 explain 76.7% (45.7 + 31.1) of the variance (Fig. 2, Table S3). Furthermore, the SVL of mature individuals from the Nicobar Islands is >90 mm, which is much larger than that of C. subcristatus and C. brevicauda. See detailed comparisons below. The syntypes of Coryphophylax maximiliani and Coryphophylax humei are morphologically similar and match all the diagnostic characters proposed for both nomina. Genetically, the representatives of samples from their respective type localities show a divergence of 0–4% (Table 2). The divergence is relatively high but may be due to the fragment chosen or sequencing errors. However, a similar range of divergence was observed in representatives of C. subcristatus, which suggests that the two nomina from Nicobar Islands are synonymous. As per Article 23, the Principle of Priority, of the Code (International Commission on Zoological Nomenclature, 1999), the name Coryphophylax maximiliani Fitzinger in Steindachner, 1867 has precedence over Stoliczka’s (1873) Coryphophylax humei and is assigned to the large-bodied population of Coryphophylax from the Nicobar Islands. The first usage of Coryphophylax maximiliani by Fitzinger, 1861 lacked an associated formal description and was correctly regarded as a nomen nudum by Wermuth (1965). The nomen was made available by Fitzinger in Steindachner, 1867 (incorrectly given as 1869 by Wermuth, 1967), where it is accompanied by a detailed description and illustration of one of the syntypes (Gemel, Gassner & Schweiger, 2019).

The type specimens of Coryphophylax maximiliani are in a fragile condition; only part of the data could be recorded for the largest specimens. The ZSI syntype of Tiaris humei is in a much better state of preservation; hence, we here redescribe the species in detail based on all examined material. The members of the genus are morphologically quite similar, and likely, additional species will be described in the near future; it is, therefore, necessary to designate lectotypes for relevant species to stabilise the taxonomy of the group. Hence, lectotypes are here designated for the Coryphophylax maximiliani from the series of specimens available at the Natural History Museum, Vienna and for the only traceable specimen of Tiaris humei at the Zoological Survey of India, Kolkata.

Coryphophylax maximiliani Fitzinger in Steindachner, 1867

Coryphophylax maximiliani Fitzinger, 1861: 387 & 397 (nomen nudum fide Wermuth, 1967)

Coryphophylax maximiliani Fitzinger in Steindachner, 1867: 30

Tiaris Humei Stoliczka, 1873: 167

Goniocephalus humii Boulenger, 1885: 293; Boulenger, 1890: 123

Goniocephalus subcristatus (partim) Smith (1935): 163; Annandale (1904): 18; Sharma (2002): 183

Coryphophylax subcristatus (partim) Manthey (2008): 99; Harikrishnan et al. (2012): 45

Coryphophylax maximiliani [authorship attributed to Steindachner, 1867] Gemel, Gassner & Schweiger, 2019

Coryphophylax Nicobar lineage (Krishnan, 2005): 80

Figures 3–7, Table 3

Lectotype (here designated): adult male NHMW 20976:5 from Nicobar Islands (Figs. 3 & 4)

Paralectotypes (n = 8): juvenile NHMW 20976:1 (SVL 57.9 mm), juvenile NHMW 20976:2 (SVL 62.1 mm), adult NHMW 20976:3 (SVL 93.6 mm, TaL 210.0 mm), juvenile NHMW 20976:4 (SVL 54.4 mm), adult NHMW 20976:6 (SVL 78.0 mm), adult NHMW 20976:7 (SVL 96.0 mm), juvenile NHMW 20976:8 (SVL 58.9 mm), juvenile NHMW 20976:9 (SVL 63.1 mm)

Additional material examined (n = 5): Lectotype of Tiaris humei (here designated), adult male ZSI 5041 from Tillanchong, Nicobar Islands; adult male BNHS 674 from Andaman and Nicobar Islands; adult male ZMB 5854, Nicobars; adult male ZMUC R36998 Camorta, Nicobar Islands; adult male ZMUC R36312 Kondul, Nicobar Islands.

Diagnosis: A large-sized species of the genus Coryphophylax, adults measuring 90–108 mm SVL with a TaL/SVL ratio of 2.68–2.73. Midbody scales in 82–85 rows, largely homogeneous in general appearance, intermixed with two fairly well-defined parallel rows of sparse, large tubercle-like scales on the trunk. The nuchal and dorsal crests well developed, composed of an erect flap of skin with slightly larger erected spines forming the apical scale row, which is very distinct in nuchal crest; skin flap differentiated from nuchal to dorsal region, with a small diastema above shoulder dorsal crest continues to 1/4 of the tail. Dorsal surface of thigh with enlarged keeled scales, one of these largest as seen in members of the genus Sitana Cuvier, 1829. 28–31 bi-mucronate lamellae on 4^th toe. Male dewlap yellow with black reticulate markings.

Description of Coryphophylax maximiliani based on examined material (Table 3):

Adults, SVL 90–108 mm (mean 96.48 ± 6.78). Head relatively long (HL/SVL ratio 0.30–0.33, mean 0.32 ± 0.010), moderately wide (HW/HL ratio 0.52–0.63, mean 0.57 ± 0.040), fairly depressed (HH/HL ratio 0.46–0.54, mean 0.49 ± 0.029), distinct from neck (Fig. 5A). Snout long (SE/HL ratio 0.37–0.42, mean 0.38 ± 0.021), bluntly conical; longer than eye diameter (OD/SE ratio 0.39–0.51, mean 0.44 ± 0.065) (Fig. 6C). Eye large (OD/HL ratio 0.14–0.19, mean 0.17 ± 0.025); pupil round, eyelids covered with small pentagonal and hexagonal scales, supraciliaries short. Snout obtusely pointed when viewed dorsally, rostral much wider than deep, bordered posteriorly by first supralabial, prenasal and dorsally by four small scales. Canthus rostralis and supraciliary edge sharp consisting of 12–14 scales, some of these are large tuberculate. Nostrils positioned centrally in a large, undivided nasal plate, bordered by 9–10 scales, including one prenasal, four postnasals and two supranasal, and in contact with rostral. Supralabials 7–10 rectangular, weakly keeled, bordered above by a single row of slightly smaller, rectangular, keeled scales. Loreal region concave, scales of the loreal region heterogeneous in size, raised not flat, keeled, some roughly hexagonal. Scales on postorbital and temporal region heterogeneous, imbricate, strongly keeled, and directed posteriorly and dorsally. Orbital scales small but not granular. Tympanum naked. Four to five large, strongly keeled, tuberculate scales running from the posterior part of orbit to the supra-tympanic region. A large tubcerculate scale on the nape on either side of the dorsal crest; a second subequal tuberculate scale in the supratympanic region and postocular region. Canthals enlarged, overlapping, becoming slightly smaller along subimbricate supraciliaries, protruding slightly laterally on supraorbital ridge. Scales on dorsal surface of snout, forehead, interorbital, and occipital region heterogeneous in size, and shape; mostly elongate, imbricate, strongly keeled longitudinally; those on snout smaller, rhomboidal, those on the supra-occiput largest. Parietal plate without pineal eye, the plate slightly larger than adjacent scales. Mental shield narrower than rostral; gular scales keeled (Fig. 6B). Infralabials 8–10. Nuchal absent, and dorsal crest present, composed of low thorn-like scales. Scales on nuchal region smaller, less than half the size of those on interorbital region, imbricate, strongly keeled. Dorsal crest comprising 57–58 raised, spike-like scales in a row on a raised flap of skin running from the posterior part of the head to the level of the vent. The crest spines high and erect with a disatema, and relatively short spine-like scales run along the vertebral column to the anterior 1/4^th of the tail. Body slender (Fig. 5A), 80–85 rows of scales around midbody, of these 16–18 rows across the belly are slightly larger than those on the dorsum (Fig. 5B); from neck to pectoral region scales largely homogenous, feebly keeled, intermixed with large strongly keeled scales. twice to thrice as big, scales on the trunk slightly larger than those on neck, imbricate, pointed, keeled, and directed posterodorsally forming regularly arranged longitudinal rows; ventral scales strongly keeled arranged in 16–18 rows, oriented backwards, subimbricate, heteroogenous in size; no precloacal or femoral pores (Fig. 5B). Number of scales MD 63–68. Distinct fold at the shoulder present. Fore and hind limbs relatively slender, tibia short (CL/SVL ratio 0.27–0.29, mean 0.28 ± 0.010); digits moderately long, ending in strong, elongate, slightly recurved claws; inter-digital webbing absent; subdigital lamellae entire, bi-mucronate, 20–25 subdigital lamellae on finger IV of manus and 28–31 on finger IV of pes; relative length of fingers and toes 4 > 3 > 5 > 2 > 1. Fore and hind limbs covered above and below with regularly arranged, enlarged, pointed, strongly keeled scales. Dorsal and dorso-lateral scales on the posterior part of the thigh enlarged, one of these scales largest and projecting as seen in members of the genus Sitana Cuvier, 1829. Tail entire; tail base swollen; tail uniformly covered with similar sized, keeled, weakly pointed, regularly arranged, posteriorly directed imbricate scales, no enlarged median subcaudal row; erect.

Distribution: Based on examined specimens and molecular data, the species appears to be distributed on the following islands in the Nicobar group of islands: Little Nicobar Is., Camorta Is., Kondul Is., Menchal Is., Katchal Is., Tillanchong Is., Trinkat Is. See Figs. 1, 7 & 8 for specific localities. Likely distributed throughout the Nicobar Islands except for Great Nicobar Island.

Comparisons: Coryphophylax maximiliani differs from its two congeners as follows: SVL 90–108 mm (vs. 53–85 mm in C. subcristatus (Fig. 9A & 9B), 42–63 mm in C. brevicauda Fig. 9C); TaL/SVL ratio 2.68–2.73 (vs. 2.04–2.51 in C. subcristatus, 1.69–2.03 in C. brevicauda); 82–85 scale rows round the body (vs. 85–100 in C. subcristatus, 110–121 in C. brevicauda); dorsal and nuchal crest comprising a skin flap expansion with large erect spine-like apical scales on the nape, with a diastema followed by relatively short spines running along the vertebral column extending to 1/4 of the tail (vs. dorsal and nuchal crest well developed, low with short spine-like scales running continuously from nape to mid-trunk in C. subcristatus, dorsal crest low and lacks large erect spine-like scales in C. brevicauda) (Fig. 8); dewlap colour yellow with black reticulate markings (vs. dewlap yellow or white without any markings in C. subcristatus, orange-red in C. brevicauda).