Lynchius megacephalus, Sánchez-Nivicela & Urgiles & Navarrete & Yánez-Muñoz & Ron, 2019

Sánchez-Nivicela, Juan C., Urgiles, Veronica L., Navarrete, María José, Yánez-Muñoz, Mario H. & Ron, Santiago, 2019, A bizarre new species of Lynchius (Amphibia, Anura, Strabomantidae) from the Andes of Ecuador and first report of Lynchius parkeri in Ecuador, Zootaxa 4567 (1), pp. 1-24 : 5-12

Lynchius megacephalus new species

Figs. 3–7 |

Holotype. An adult female ( MZUA.AN.0633) collected in September 2013 by Christian Nieves and Danny Villalta at the Ecological Conservation Area Tinajillas-Río Gualaceño (3.011677° S, 78.614464° W [WGS84], elevation: 2770 m), Morona Santiago province, Ecuador ( Fig. 2 ).

Diagnosis. A member of the genus Lynchius , as defined by Motta et al. (2016). We base its assignment to Lynchius on the phylogeny ( Fig. 1 ). Lynchius megacephalus is a large species (adult female SVL = 41.8 mm; males unknown) diagnosed by having: (1) skin on dorsum of head, body, flanks and limbs with many low subconical and rounded tubercles; with pronounced and irregular dermal ridges (more noticeable in life); postocular fold ›‹- shaped; dorsolateral fold absent; middorsal fold present, low; skin of venter smooth; discoidal and thoracic folds present; (2) tympanic membrane and annulus distinct, its diameter 64% of eye diameter, upper edge of tympanum obscured by supratympanic fold; three postrictal tubercles; (3) head wider than long (HW/HL=1.3) and wider than the body; snout rounded in dorsal and lateral views; nostrils laterally oriented; canthus rostralis slightly concave; upper eyelid covered by small scattered tubercles; (4) cranium heavily ossified, with spiculate dermal bones completely covering external surface of cranium; cranial crests present; (5) dentigerous processes of vomers prominent, oblique; choana rounded; tongue cordiform, attached to the floor of the mouth along 73% of its length; (7) digits long and slender; tips of digits narrow, circumferential groves absent and lateral fringes narrow, interdigital webbing absent; terminal phalanges knob-shaped; (8) finger I as long as II; subarticular tubercles prominent; few supernumerary tubercles, low and smaller than subarticular tubercles; single palmar tubercle; thenar tubercle prominent, almost the same size of the palmar tubercle; (9) ulnar tubercle absent or hidden by dermal tubercles in arms; (10) toe III as long as toe V; subarticular tubercles prominent toes III and V reaching proximal border of second subarticular tubercle of Toe IV; supernumerary tubercles absent; (11) inner metatarsal tubercle elongate, prominent, as the outer metatarsal tubercle; (12) heel and tarsal tubercles absent or hidden by dermal tubercles in legs.

Comparison with similar species. Lynchius megacephalus differs from other species of Lynchius by having extensive exostosis on all the external surface of skull and head wider than body. Lynchius flavomaculatus and L. parkeri are the only other congeneric species with exostosis (condition described as rugosity in L. parkeri )

but it differs in extent (circumscribed to the frontoparietals vs. present in the frontoparietals, squamosal, nasals and pars facialis in L. megacephalus ). The new species differs from L. nebulanastes and L. parkeri by having a distinct tympanic membrane and larger size, from L. oblitus by having a head wider than body and by lacking dorsolateral folds, and from L. simmonsi and L. tabaconas by having cranial crests. Lynchius megacephalus can be further distinguished from L. flavomaculatus , L. nebulanastes , L. oblitus , L. parkeri , and L. tabaconas by lacking, in life, bright coloration (yellow, green, or orange) in dorsum, venter or flanks. Lynchius megacephalus is very similar to L. simmonsi because both species are black or dark brown. However, in L. simmonsi the dorsum has spicule-like warts (skin of dorsum with tubercles and projected dermal ridges in L. megacephalus ). Additionally, L. simmonsi lacks an occipital fold (present in L. megacephalus ) and Finger I longer than Finger II (Finger I = Finger II in L. megacephalus ).

Description of the holotype morphology. Adult female ( Fig 3 ¯5). Head wider than long, and wider than the body. Snout short, rounded in dorsal and lateral view. Canthus rostralis slightly convex. Nostrils in anterolateral direction. Upper eyelid tubercles small and rounded. Tympanum and tympanic annulus evident; 64% of eye diameter. Dorsal skin shagreened with small subconical and rounded tubercles; dorsal and postocular folds with pronounced and irregular dermal ridges; middorsal fold low. Skin on venter smooth; discoidal and thoracic folds present. Thin arms; upper arm 1/3 length of the lower arm. Subconical and rounded tubercles in dorsal surface of arms and legs. Supernumerary palmar tubercles present. Fingers long and slender, tips narrow; lateral fringes narrow; subarticular tubercles projecting. Finger I as long as II; few supernumerary tubercles, low and smaller than subarticular tubercles; thenar tubercle prominent, almost the same size of palmar tubercle. Relative length of fingers: I=II=IV<III. Toe III almost as long as toe V, without supernumerary tubercles. Relative length of toes: I<II<III<V<IV.

Description of the holotype osteology. The cranium ( Fig. 6 ) is robust, 5/4 times wider than long and its maximum height is> 65% of the length of the skull. The frontoparietals are wide, fused in the medial region and expanded laterally posteriorly. Integumentary-cranial co-ossification is evident. The frontoparietal fontanelle, nasals, maxilla, sphenethmoid, premaxillae, lamella alaris, and squamosal are covered by dermal bone. The frontoparietals, nasals, pars facialis of the maxillae, the zygomatic, and otic ramus of the squamosal have exostosis. All dermal bones have a spiculate ornamentation, which is most notorious in the frontoparietal region, forming a crown that reaches ¼ of the eye orbit. This crown is projected towards the anterior region of the cranium. The size of the spicules decreases towards the posterior region, forming a W-shaped crest. The nasals and sphenethmoids are ossified and large. The nasals cover extensively the olfactory capsule. The alary process of the premaxilla is well developed. The zygomatic ramus of the squamosal articulates with the maxilla and quadratojugal. The oto-occipital is well ossified with coarse epiotic eminences. The crista parotica are long and coarse. The operculum is present. The occipital condyles are pedunculated. The lamella alaris is long, extending to the dorsal edge of the maxilla, behind the eye orbit, posteriorly forming an acuminated projection at the end of the squamosal. The co-ossification, exostosis, and the extent of the nasals, and quadratojugal form a sturdy skull. The maxillary teeth are curved, spreading along the maxillary arcade, but not reaching the pterygoid. The prevomers are large. The dentigerous processes of vomers are prominent and narrow, with seven to nine pointed teeth. The neopalatines are wide, extending from the maxilla to the sphenethmoid and with a notorious thickening in the middle-anterior region. The cultriform process of the parasphenoid is long, ending in the mid-posterior portion of the sphenethmoids, between the neopalatines. Two posteromedial ossified process can be distinguished posteriorly on the hyoid.

The vertebral column ( Fig. 7A ) has eight procelic presacral vertebrae, I and II fused. All vertebrae show transversal processes: III = sacral diapophyses> IV> V = VI = VII = VIII> II. The orientation of these transversal processes is slightly perpendicular in vertebrae III and VIII, anterolateral in II and posterolateral in IV, V, VI, and VII. The neural spines are evident in all the presacral vertebrae. Diapophyses sacra without sesamoid cartilage at the edge, extending distally and posterolaterally. Sacrococcygeal articulation with a double condyle. The urostyle ( Fig. 7A ) is shorter than the presacral spine and have a long middorsal crest. The ilium is long. The ilia are thin, Ushaped in dorsal and ventral view. The pubis is ossified.

The pectoral girdle ( Fig. 7B ) is arciferal and formed by strong and ossified coracoids, scapulae, suprascapulae, and thin clavicles. The clavicles are concave with medial tips distinctly separated from one another. The lateral edge of the clavicle articulates with the pars acromialis of the scapulae. The coracoids are coarse and heavily concave at the anterior edge and slightly concave at the posterior edge. The glenoid fossa is wider than the union with the epicoracoids.

The humerus is thin, about the same length as the radioulna ( Fig. 7C ). The deltoid crest is well developed, reaching the middle of the humerus. The radioulna is fused from the middle to the posterior region. The manual phalange formula is 2-2-3-3, the terminal phalanges have an acute apical knob. The prepollex is short, ¼ the length of the proximal phalange of finger II. The femur is 1/3 longer than the tibiofibula. The tibia and fibula are fused in their proximal and distal edges. The phalange formula in the foot is 2-2-3-4-3. A small prehallux is present ( Fig. 7D ).

Coloration of the holotype. In life ( Fig. 3 ), dorsolaterally, the head, body, and limbs are brown with irregular dark brown spots, in the back, these spots cover the dermal ridges and, in the limbs, form a series of transverse bars. In ventral view, the belly, and limbs are grayish-brown with irregular spots brown. Throat is dark brown. Fingers I and II are cream from the most proximal subarticular tubercle to their distal end. The iris is golden with reticulated black lines, a median horizontal black streak, and a light-blue sclera can be distinguished at the upper edge of the eye.

In preservation ( Fig. 4 ), dorsolaterally, the head, back, flanks, limbs, throat, and fingers I and II have the same color as in life. Ventrally, belly and limbs have a light brown coloration, with darker brown irregular spots.

Etymology. The name megacephalus is derived from the Greek mega meaning big and cephala meaning head. The name refers to the wide and robust head of this new species. The epithet is used as a noun in apposition.

Distribution and Natural history. Lynchius megacephalus is only known from one specimen collected at the type locality in the Tinajillas-Río Gualaceño Ecological Conservation Area, Morona Santiago province, 2770 m of elevation. The holotype was collected during the night (approximately 22h00) on the forest floor, between leaflitter in the middle of a heavy rainy week. The ecosystem is Eastern Montane Forest (according to Ron et al. 2018 natural regions). The forest at the type locality is characterized by small streams and leaflitter> 10 cm thick ( Urgilés & Nieves 2014). The dense canopy can exceed 20 m height. The vegetation includes species of the genus Oreopanax, Weinmannia, Cinchona, Chusquea , and Baccharis (Baez et al. 2013) . The new species was recorded in sympatry with Pristimantis versicolor , P. andinognomus , P. atratus , P. cryophilius , P. gualacenio , P. proserpens , P. spinosus , and an undescribed Lynchius species similar to L. flavomaculatus .

Conservation Status. The scarcity of records of L. megacephalus at the type locality, a natural reserve that has been thoroughly surveyed by herpetologists since 2013, could indicate either that the population is small or that capture probabilities are low as result of its habitat preferences. Because nothing is known about its natural history and population status, we suggest assigning the new species to the Data Deficient category of the Red List (according to IUCN 2001 criteria).

Figures

FIGURE 1. Phylogenetic relationships of Lynchius species. Maximum-likelihood tree obtained from analyses of mitochondrial (12S, 16S, and ND1) and nuclear (RAG and Tyr) DNA sequences from 14 specimens of Lynchius (excluding outgroup taxa). Numbers before slashes correspond to Bayesian posterior probabilities (PP); asterisks (*) represent PP = 1.0. Numbers after slashes are ML bootstrap support (BB) values; asterisks (*) represent BB = 100. PP and BB values <0.50 or 50, respectively are not shown. Museum number and country are shown for each specimen. Locality is also shown for L. megacephalus sp. n. and L. parkeri. Locality details, as well as voucher, GenBank accession numbers, and literature references are provided in Appendix 2.

FIGURE 2. Map showing the type locality of the new species Lynchius megacephalus (yellow dot) from Ecological Conservation Area Tinajillas Río Gualaceño-Morona Santiago province, Ecuador (elevation: 2800 m), and localities of Lynchius parkeri (red squares) from Yacuri National Park, Laguna Jimbura-Loja province, Ecuador (elevation: 2990–3397 m) and previously known localities from Peru (red squares with a black point). The bold black line represents the boundary between Ecuador, Peru, and Colombia. Locality details are shown in Appendix 2. Abbreviations are Colombia = COL, Ecuador = ECU, Peru = PER.

FIGURE 3. Holotype of Lynchius megacephalus sp. n., female MZUA.AN.0633 (SLV 41.8 mm) in life.

FIGURE 4. Holotype of Lynchius megacephalus sp. n. in preservative. (A) Dorsal view, (B) ventral view, (C) profile view of the head, (D) lateral view.

FIGURE 5. Ventral view of A) hand and B) foot of the holotype of Lynchius megacephalus sp. n. (hand length 5.2 mm, foot length 13.4 mm).

FIGURE 6. Skull of holotype of Lynchius megacephalus sp. n. (adult female) in (A) dorsal (B) ventral, and (C) lateral view, with visible exostosis and ornamentation (with wrinkled appearance), and (D) lateral view of the mandible (grey region represents the site of the articulation of the maxilla with the quadratojugal).

FIGURE 7. (A) Vertebral column and pelvic griddle, (B) pectoral grid, C) arm and D) foot of the holotype of Lynchius megacephalus, sp. n (adult female).