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| Stefania maccullochi Kok, 2023 |
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, µCT scanning, Symplesiomorphy, Systematics, Taxonomy
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| 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) |
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| Phylogenetic relationships of the Stefania riveroi clade modified from [Kok, et al. 2017], 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 P. J. R. Kok (Stefania maccullochi sp. nov. and S. riveroi) and D. B. Means (S. ayangannae and S. coxi) |
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| 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 P. J. R. Kok. |
Stefania maccullochi sp. nov.
Stefania sp. Villarreal et al. 2002: 48.
Stefania sp. “Wei-Assipu” Kok et al. 2012: Supplemental Information.
Stefania sp. 6 Kok et al. 2017: 175–176.
Definition and diagnosis:
Stefania maccullochi sp. nov. is characterized by the combination of the following morphological characters that distinguish it from all known congeners: (1) a large species of Stefania, max SVL in preserved females 72.9 mm, 54.6 mm in preserved males; (2) head not distinctly longer than wide, about as wide as long; (3) canthus rostralis smooth, prominent, rounded, concave, canthal stripe present in life, sometimes inconspicuous, rarely broad; (4) loreal region with a few low tubercles; (5) upper eyelid mostly smooth, absence of enlarged triangular appendage on its posterior upper part, although a conical tubercle may be present medially; (6) frontoparietal ridges conspicuous, low (in life/preservative); (7) frontoparietal ...
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| 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 P. J. R. Kok |
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| 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 P. J. R. Kok. |
Etymology: The specific epithet maccullochi is a noun in the genitive case, honoring Canadian herpetologist Ross Douglas MacCulloch (born 1948) for his seminal contribution to the systematics and taxonomy of the genus Stefania in particular, and to the knowledge of the amphibians and reptiles of Guyana in general.
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| 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 P. J. R. Kok. |
Conclusions:
Stefania maccullochi sp. nov. is a microendemic and morphologically/taxonomically cryptic species belonging to the S. riveroi clade. The S. riveroi clade, as presently understood, is restricted to the highlands and uplands (1200–2400 m elevation) of the Eastern Tepui Chain in Venezuela/Guyana/Brazil, and the Pakaraima Mountains in western Guyana. The new species is only known from the small summit (ca. 3 km2) of Wei-Assipu-tepui, an isolated table-top mountain at the border between Guyana and Brazil. Stefania maccullochi sp. nov. is considered critically endangered according to IUCN criteria. Although morphologically highly similar to S. riveroi from the summit of Yuruaní-tepui, a table-top mountain in Venezuela, S. maccullochi sp. nov. has been shown to be sister to S. ayangannae, a species occurring on two major tepuian massifs in western Guyana. Stefania maccullochi sp. nov. and S. ayangannae are easily diagnosed by size, osteology, skin texture, and color pattern. The striking morphological similarity between S. riveroi (sister to the three other species in the S. riveroi clade) and S. maccullochi sp. nov. is probably a consequence of symplesiomorphy and/or homoplasy. Examination of the skeletal morphology of the new species and comparison with congeners highlighted a previously unnoticed osteological synapomorphy for the genus: the presence of a distal process on the third metacarpal. This description brings the number of described Stefania species to 20, all (near-) endemic taxa inhabiting the biodiverse Pantepui biogeographical region.
Philippe J. R. Kok. 2023. Bones and All: A New Critically Endangered Pantepui Species of Stefania (Anura: Hemiphractidae) and A New Osteological Synapomorphy for the Genus. Zoological Letters. 9: 11. DOI: 10.1186/s40851-023-00209-6