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.

Out of sight, but not out of mind: a name for the Stefania (Anura: Hemiphractidae) from the summit of Murisipán-tepui (Bolívar State, Venezuela)

“…It should be noted that two subtle osteological characters reported in this study – i.e. the distinctions between the absence of contact vs. the contact or fusion of the posterodorsal projection of the maxilla with the orbital ramus of the squamosal, and of the maxillary process of the nasal with the maxilla – remain speculative and could merely reflect different resolutions of the µCT scans (see Table S1 for details) or bias in the interpretation of µCT-scan reconstructions (see Kok 2023). The diagnostic value of these characters should be confirmed by analysing a larger number of specimens scanned at similar resolution.…”

“…Morphometric data were taken from the preserved specimens to the nearest 0.01 mm (rounded to 0.1 mm) with digital callipers (MarCal 16 EWRi). Morphological comparisons are based on examination of museum specimens (see Appendix S1) and published descriptions (Boulenger 1904, Rivero 1961, 1968, 1970, Duellman & Hoogmoed 1984, Myers & Donnelly 1997, Señaris et al 1997, MacCulloch & Lathrop 2002, 2006a, b, Barrio-Amorós & Fuentes-Ramos 2003, MacCulloch et al 2006, Carvalho et al 2010, Kok 2023). Description of external morphological characters follows Kok & Kalamandeen (2008).…”

“…Description of external morphological characters follows Kok & Kalamandeen (2008). Definition, diagnosis, and description of the holotype mostly follow the scheme of MacCulloch & Lathrop (2002), with amendments as provided in Kok (2023) for ease of comparison.…”

“…The hemiphractid frog genus Stefania currently contains 20 species (Kok 2023) of small (max. 54.8 mm in S. ayangannae ) to large (max.…”