Bones and all: a new critically endangered Pantepui species of Stefania (Anura: Hemiphractidae) and a new osteological synapomorphy for the genus

Abstract

The hemiphractid frog genus Stefania is one of the many ancient (near-) endemic lineages of vertebrates inhabiting the biodiverse Pantepui biogeographical region in the Guiana Shield Highlands of northern South America-the famous "Lost World" of Arthur Conan Doyle. Previous molecular analyses of the genus Stefania have indicated that species boundaries and phylogenetic relationships are often incongruent with morphological traits in that clade. A substantial number of "taxonomically cryptic" species, often microendemic, remain to be described. This is notably the case for an isolated population from the summit of Wei-Assipu-tepui, a small table-top mountain at the border between Guyana and Brazil. That population was previously known as Stefania sp. 6 and belongs to the S. riveroi clade. The new species is phylogenetically distinct, but phenotypically extremely similar to S. riveroi, a taxon found only on the summit of Yuruaní-tepui in Venezuela and recovered as sister to all the other known species in the S. riveroi clade. The new taxon is described based on morphology and osteology. Data about genetic divergences within the S. riveroi clade are provided. A new synapomorphy for the genus Stefania is proposed: the presence of a distal process on the third metacarpal. Amended definitions are offered for the three other species in the S. riveroi clade (S. ayangannae, S. coxi, S. riveroi). The new species should be listed as Critically Endangered according to IUCN criteria.

Keywords: Endemism; Genetic distances; Homoplasy; Morphology; Osteology; Symplesiomorphy; Systematics; Taxonomy; µCT scanning.

Fig. 1

Summit of Wei-Assipu-tepui, terra typica of Stefania maccullochi sp. nov. A Aerial photograph taken facing southwest (photo Adrian Warren). B Aerial photograph taken facing northwest (photo by the author)

Fig. 2

Distribution map of the Stefania riveroi clade as currently understood. Locality data are based on specimens examined (see Additional file 2: Appendix), literature records [–13], and GBIF [14]. Type localities for S. ayangannae and S. coxi are Mount Ayanganna, Guyana. Inset photos by the author (S. maccullochi sp. nov. and S. riveroi) and D. B. Means (S. ayangannae and S. coxi)

Fig. 3

Holotype of Stefania maccullochi sp. nov. (NHMUK 2023.3184, female, 62.9 mm SVL) A Dorsolateral view in life. B Ventral view of the specimen freshly euthanized. Photos by the author

Fig. 4

Holotype of Stefania maccullochi sp. nov. (NHMUK 2023.3184, female, 62.9 mm SVL) in ethanol preservative A. Dorsal view. B. Ventral view. Photos by the author

Fig. 5

Palm (A) and sole (B) of the preserved holotype of Stefania maccullochi sp. nov. (NHMUK 2023.3184). Photos by the author

Fig. 6

Three-dimensional model of the complete skeleton of the holotype of Stefania maccullochi sp. nov. (NHMUK 2023.3184) based on µCT imagery. A Dorsal view. B Ventral view. C Left lateral view. White arrows indicate the presence of a distal process on the third metacarpal, a new synapomorphy for the genus. Central inset highlights the third metacarpal of the right hand of the holotype in ventral view and shows the distal process

Fig. 7

Three-dimensional model of the cranium of the holotype of Stefania maccullochi sp. nov. (NHMUK 2023.3184) based on µCT imagery. A Dorsal view. B Ventral view. C Frontal view. D Left lateral view. Abbreviations: ang Angulosplenial, ang.cp Coronoid process of the angulosplenial, col Columella, c.p Cultriform process, d Dentary, exo Exoccipital, fp Frontoparietal, lam.p Lamina perpendicularis, mmk Mentomeckelian, mx Maxilla, mx.pp Posterodorsal projection of the maxilla, na Nasal, na.mp Maxillary process of the nasal, neo Neopalatine, p.f  Pars facialis, pmx Premaxilla, pmx.ap Alary process of the premaxilla, pmx.lp Lateral process of the premaxilla, pmx.pp Palatine process of the premaxilla, pro Prootic, psp Parasphenoid, psp.ar Alary process of the parasphenoid, psp.pp Posteromedial process of the parasphenoid, pt Pterygoid, pt.ar Anterior ramus of the pterygoid, pt.mr Medial ramus of the pterygoid, pt.pr Posterior ramus of the pterygoid, qua Quadratojugal, smx Septomaxilla, sph Sphenethmoid, squa Squamosal, squa.or Otic ramus of the squamosal, squa.vr Ventral ramus of the squamosal, squa.zr Zygomatic ramus of the squamosal, v Vomer

Fig. 8

Phylogenetic relationships of the Stefania riveroi clade modified from [6], based on 2301 base pairs of nuclear and mitochondrial DNA (Bayesian statistical supports are provided at nodes), and comparison of crania in dorsal and lateral views. Circles and arrows highlight potential diagnostic characters: blue circles highlight absence/presence/location of a constriction in the frontoparietal bones; blue arrows highlight the condition of the frontoparietal crests; red arrows highlight the condition of (1) the contact between the posterodorsal projection of the maxilla and the orbital/zygomatic ramus of the squamosal, and (2) the contact between the maxillary process of the nasal and the maxilla. Inset photos by the author (S. maccullochi sp. nov. and S. riveroi) and D. B. Means (S. ayangannae and S. coxi)

Fig. 9

Phylogenetic relationships of the Stefania riveroi clade (modified from [6]), and comparison of crania in frontal view. Circles and arrows highlight diagnostic and potentially diagnostic characters: blue arrows highlight the condition of the frontoparietal crests; green arrows highlight the condition of exostosis; blue circles highlight the condition/absence of an indentation along the anteromedial base of the alary process of the premaxilla

Fig. 10

Main color pattern variation in Stefania maccullochi sp. nov. A IRSNB 15854, male. B NHMUK 2023.3188 (PK2098), female. C IRSNB 15855, female. D NHMUK 2023.3193 (PK2148), male. E NHMUK 2023.3192 (PK2137), male. F NHMUK 2023.3187 (PK2084), male. Photos by the author

Fig. 11

Main macrohabitats on the summit of Wei-Assipu-tepui. The cliff visible in the background of A is the eastern flank of Roraima-tepui. Photos by the author

Fig. 12

Various females of Stefania maccullochi sp. nov. carrying eggs and juveniles. A and B. Uncollected female carrying 9 juveniles. C. NHMUK 2023.3190 (PK2122), carrying 10 eggs/metamorphs. D. NHMUK 2023.3185 (PK2063), carrying 2 near-term juveniles. E and F. IRSNB 15853, carrying 4 near-term juveniles. Photos by the author

Fig. 13

Main color pattern variation in Stefania riveroi, and illustration of the other known species in the Stefania riveroi clade. A. S. riveroi, IRSNB 15719, female. B. S. riveroi, IRSNB 15715, male. C. S. riveroi, IRSNB 15703, male. D. S. riveroi, IRSNB 15740, female. E. S. coxi, uncatalogued, female carrying 6 eggs. F. S. ayangannae, uncatalogued/unsexed. Photos by the author, except E and F by D. Bruce Means