The microhylid genus Oreophryne reaches its greatest diversity in the New Guinea region, where more than 60 species have been documented to date. Most Oreophryne are small (<30 mm SVL) and only three species, O. anthonyi, O. idenburgensis and O. inornata, exceed 40 mm SVL adult body size. Here we describe a fourth large species of Oreophryne that was collected in 1998 from the mountains of Papua Province in western New Guinea. In having a cartilaginous connection between the procoracoid and scapula it is most similar to O. idenburgensis, a species known only from the mountains of central-western New Guinea but differs from that species in a suite of morphological characters including a broader head, a hidden (vs. visible) tympanum and a more pointed snout.

Central cordillera, frog, Indonesia, morphology, new species, taxonomy

Oreophryne Boettger, 1895 is the most diverse genus of microhylid frogs in the New Guinea region with 64 species recognised from mainland New Guinea and adjacent islands to date (Richards and Günther 2019, Frost 2022). Rates of discovery and description have increased dramatically in the past two decades with more than two thirds of Oreophryne species (45/64) from the New Guinea region described since 2000 (Kraus 2013, 2016, 2017a,b, Günther et al. 2018, Richards and Günther 2019) and numerous additional species in collections awaiting description. The majority of these are small species, with adult body lengths rarely exceeding 35 mm (Menzies 2006, Kraus 2016). Just three species, O. anthonyi (Boulenger, 1897), O. idenburgensis Zweifel, 1956 and O. inornata Zweifel, 1956 reach body sizes in excess of 40 mm. Two of these, O. anthonyi and O. inornata, occur in southeastern New Guinea (Zweifel 1956, Menzies 2006), while O. idenburgensis is currently known from a single location on the northern slopes of the central cordillera in Papua Province, western New Guinea (Zweifel 1956, IUCN 2020).

Exploration of New Guinea’s mountainous interior has revealed an exceptionally rich microhylid frog fauna. In western New Guinea, important contributions to knowledge about the region’s Microhylidae were made during a series of expeditions organised by Conservation International’s Rapid Assessment Program (RAP) in collaboration with the Indonesian Institute of Science (LIPI) (Mack and Alonso 2000, Richards and Suryadi 2002). These surveys documented numerous undescribed microhylid species, several of which have subsequently been described including members of the genera Choerophryne van Kampen, 1914 (Günther et al. 2018), Oreophryne (Günther et al. 2001, 2018) and Xenorhina Peters, 1863 (Günther and Richards 2005). Among the species discovered during these RAP surveys is a large (>40 mm SVL) species of Oreophryne that resembles O. idenburgensis but differs from that species by a suite of morphological characters. Here we provide a description of the new species.

The male holotype was located at night by its advertisement calls. It was euthanized in an aqueous chlorobutanol solution (Gamble 2014), fixed in 5 % formalin and transferred to 70 % ethanol within two days of fixation. The following measurements were taken with a digital calliper (> 10 mm) or with a binocular dissecting microscope fitted with an ocular micrometer (< 10 mm) to the nearest 0.1 mm from the preserved specimen: SUL – snout-urostyle length from tip of snout to posterior tip of urostyle bone. SUL is generally slightly shorter than snout-vent length ( SVL); as the measurement error is higher in the latter, we prefer to use the former. Both measurements are sufficiently similar (unpublished data) that, where relevant, we compared our SUL measurements with SVLs presented by other authors; TL – tibia length: external distance between knee and tibio-tarsal articulation; TaL – length of tarsus: external distance between tibio-tarsal and tarsal-metatarsal joints held at right angles; FtL – length of 4th toe, from tip of fourth toe to proximal end of inner metatarsal tubercle; T4D – transverse diameter of disc of 4th toe; T1D – transverse diameter of disc of first toe; HdL – length of 3rd finger, from tip of third finger to proximal edge of palm; F3D – transverse diameter of disc of 3rd finger; F1D – transverse diameter of disc of first finger; Head length and Tympanum diameter could not be measured because external tympana are absent; HW – maximum head width; SL – snout length, from an imaginary line connecting the centres of the eyes to tip of the snout; EST – distance from anterior corner of orbital opening to tip of snout; END – distance from anterior corner of orbital opening to centre of naris; IND – internarial distance between centres of nares; ED – eye diameter, from anterior to posterior corner of orbital opening.

Structure of the procoracoids was determined by superficially dissecting the chest region and staining cartilaginous elements with Alcian Blue. Colour of the holotype in life is described from digital photographs, and of preserved specimen from direct observations. Most colours were determined according to a colour matching system created and administrated by the German RAL GmbH (https://en.wikipedia.org/wiki/RAL colour_standard). When it was not possible to find an exact match between observed colours and RAL colour numbers, the most similar RAL number was chosen.

Comparative material was examined at the American Museum of Natural History, New York (AMNH), Natural History Museum, London (BMNH), Naturalis, Leiden (RMNH), Museum of Comparative Zoology, Harvard(MCZ), South Australia Museum, Australia (SAMA), Museum für Naturkunde Berlin (ZMB), and Museum Zoologicum Bogoriense, Cibinong, Indonesia (MZB). Additional information for comparisons was taken from Zweifel (1956). SJR and JCUNQ refer to original field collection numbers of S.J. Richards.The holotype is deposited in the collection of the Museum Zoologicum Bogoriense (MZB). We examined the following comparative material of large Oreophryne species: Oreophryne anthonyi, BMNH 1947.2.12.34–40 (cotypes, Papua New Guinea, Mount Victoria); Oreophryne idenburgensis, RMNH 10473, AMNH A49665–6, 49668 (paratypes, Indonesia, Papua Province, 18 km SW Bernhard Camp); Oreophryne inornata, BMNH 1956.1.1.21, AMNH A56731, 56903–4, 56984, 57259 (paratypes, Papua New Guinea, Goodenough Island). Additional material of Oreophryne species examined is listed in Richards and Iskandar (2000), Günther et al. (2001), Günther (2003a,b), Zweifel et al. (2005), Günther et al. (2009) and Günther (2015).

The description of Oreophryne chlorops brings to 64 the number of Oreophryne species known from the New Guinea region (Frost 2022). About 30 other members of the genus exhibit a cartilaginous connection between the procoracoid and scapula (Günther et al. 2018) but only one of these approaches the size of O. chlorops (Menzies 2006, Kraus 2016). The only Oreophryne of similar size that has a cartilaginous connection between the procoracoid and scapula is O. idenburgensis, which is also the species most proximate geographically to O. chlorops (Fig. 2). Oreophryne idenburgensis is known from a similar altitude (~2,100 m a.s.l.; Zweifel 1956) at a single location on the northern edge of New Guinea’s central cordillera, about 280 km to the west of the type locality for O. chlorops (Fig. 2). Given the morphological similarity of these two species they are probably closely related, but a better understanding of the phylogenetic relationships among members of this diverse genus, including whether it represents a monophyletic assemblage, must await a detailed molecular study.

The blue-green iris of O. chlorops is unusual among Oreophryne species, being reported previously only for O. ezra Kraus and Allison, 2009, although the iris colour of a number of species that were described solely from preserved specimens remains undocumented. However, O. ezra is a small (SVL< 30 mm) species from Sudest Island in far-eastern New Guinea (Kraus and Allison 2009) and has a ligamentous connection between the procoracoid and scapula so it is unlikely to be closely related to the new species described here. Unfortunately, the iris colour of O. idenburgensis is unknown.

Oreophryne chlorops is currently known only from a single specimen, which was calling from 4 m high in a Pandanus tree on steep, rugged terrain that was difficult to traverse on foot. No other animals were heard calling, and the species has not been detected on subsequent surveys in the mountains of western New Guinea (S. Richards, unpublished data). Given the remoteness of the type locality (Mack and Alonso 2000), which was accessed by helicopter, the likelihood of returning to this location and obtaining additional material of O. chlorops is extremely low. Descriptions of new microhylid frogs based on limited samples, including singletons, is common (Allison and Kraus 2000, Günther et al. 2016, Günther and Richards 2021) and we believe that the unique specimen of O. chlorops is sufficiently distinct from all congeners to warrant formal recognition.

We thank the Indonesian Institute of Science (LIPI) for permission to undertake research in Papua Province and for providing export permits. Amir Hamidy, Ibu Mumpuni and Ibu Lili at the Museum Zoologicum Bogoriense were particularly helpful with approving export permits and registering specimens. This research was part of Conservation International’s Rapid Assessment Program, and their assistance is greatly appreciated. Funding support was provided by the CI-USAID Cooperative agreement #PCE-5554-A-00-4028-00. SJR and DTI are grateful to Andy Mack, Dr Jatna Supriatna, and Burke Burnett for their support in the field. P.T. Freeport Indonesia provided logistical support. We thank the following curators and collection managers for access to specimens in their care: Carolyn Kovach, Mark Hutchinson and Dominic Capone (SAMA); Barry Clarke (BMNH); Linda Ford and Darrel Frost (AMNH); José Rosado (MCZ); Marinus Hoogmoed and Pim Arntzen (Naturalis); Giuliano Doria (MSNG); Miguel Vences and Axel Groenveld (ZMA); and Frank Tillack (ZMB). Special thanks are due to Lauren Vonnahme and David Kizirian (AMNH) for lending material and taking photographs of paratypes of Oreophryne idenburgensis and to Elke Günther for her help to layout Figs 1 and 4.