Hylomys vorax Hinckley, Lunde & Hawkins, 2024

Hinckley, Arlo, Camacho-Sanchez, Miguel, Chua, Marcus A H, Ruedi, Manuel, Lunde, Darrin, Maldonado, Jesús E, Omar, Hasmahzaiti, Leonard, Jennifer A & Hawkins, Melissa T R, 2024, An integrative taxonomic revision of lesser gymnures (Eulipotyphla: Hylomys) reveals five new species and emerging patterns of local endemism in Tropical East Asia, Zoological Journal of the Linnean Society 202 (2), pp. 1-33 : 20-22

Hylomys vorax Hinckley, Lunde & Hawkins , sp. nov.

Hylomys suillus maxi Miller, 1942: 109–111 .

Hylomys suillus maxi Best, 2018: 328 .

ZooBank registration: urn:lsid:zoobank.org:act: BA2B0BCE-AF92-4583-8C74-1A3EAA60AE7B.

Holotype: USNM 271034 , an adult male collected by Frederick A. Ulmer, Jr on 1 May 1939 . The specimen consists of a museum study skin with accompanying cranium and mandible; skin well prepared, with a small hairless patch on the two thighs and the most external toe of the left hindfoot missing (clipped for DNA extraction), otherwise in good condition; skull well prepared (with some remaining dried tissue attached, allowing for subsequent historical DNA extraction), but has damaged pterygoid processes, left P2 crown, and ectotympanic bone of the right bulla. Total length 148 mm, tail 22 mm (17.5 % HB), hindfoot 27.5 mm, ear length 19 mm, weight 42.5 g. Skull measurements in Supporting Information, Table S2. 3D surface scans of this holotype skull are available at: https://doi.org/10.17602/ M2/M560018 (cranium); https://doi.org/10.17602/M2/ M560022 (mandible). Pictures of this holotype skull and skin are shown in Figure 9A and the Supporting Information, Figure S9 , respectively. DNA sequences associated with this holotype have been deposited in GenBank: OR138102 and OR554454 .

Type locality: ‘ Bivouac No. 5, Loser Trail, Atjeh’ (now known as Mt. Leuser trail, Aceh, Sumatra, Indonesia). This locality is shown in the map of de Schauensee and Ripley (1939), and we have estimated it at c. 3.85º N, 97.12º E, 2408 m a.s.l.The type locality could be georeferenced after we located two flanking sampling sites of the George Vanderbilt Sumatran Expedition (Ulmer’s field notes, Schauensee and Ripley 1939, Miller 1942): Mt. Leuser peak no. 1 (3.791072º N, 97.211351º E) and Blangbeke (c. 3.891223º N, 97.152307º E). Blangbeke could be easily georeferenced by the authors of this manuscript since it is the only ‘blang’ (open area) with a river on a ‘flat plateau of about 7000 ft’ found to the south of ‘Base camp (3600 ft), Blangnanga’, which is 20 km West of the town of Blankejeren according to Fred Ulmer’s notes. The river is called ‘Waih Blang Bebeke’, which resembles the locality’s name. The type locality ‘ Bivouac No. 5’ is shown on the map of de Schauensee and Ripley (1939), just south of the Waih Blang Bebeke headwater. The approximate bivouac location was estimated in this manuscript through the combination of this map and information retrieved with Google Earth topographic layers and street view, and Fred Ulmer’s references and pictures housed at the ANSP Mammal Department archives.

Paratypes (9): ANSP 20379 , 20380 , 20381 : same as type locality ; ANSP 20374 , 20375 , 20376 , 20377 , 20378 , and USNM 271033 : ‘Blangbeke, Atjeh’ (= Blang Beke , Aceh, Sumatra; elevation 2073– 2134 m a.s.l.). Paratype ANSP 20377 was illustrated by Frederick A. Ulmer (Supporting Information, File S1, Fig. S11 )

Representative DNA sequences: Deposited in GenBank with the following accession numbers: OR138101 and OR138102 (mitochondrial genomes, two representatives), OR554452-OR554454 ( GHR, three representatives). DNA sequences associated with the following voucher specimens: USNM 271034, ANSP 20377, 20380.

Etymology: The specific name acknowledges the voracious behaviour that Frederick Ulmer, the collector of the type series, described in his field notes: ‘They were voracious beasts often devouring the whole bait before springing the trap. Ham rind, coconut, meat, and walnuts were eaten. One shrew partially devoured the chicken head bait of a steel trap before getting caught in a nearby Schuyler trap baited with ham rind’ ( USNM 271033). We recommend the common names Leuser Gymnure, Salak Ba’a Leuser, and Gimnuro de Leuser, in English, Malay, and Spanish, respectively.

Diagnosis: A medium-sized Hylomys (average HB = 123 mm, W = 44.4 g) characterized by a thick and soft, dark brown fur, a long and monocoloured black tail (average T = 21.4 mm; T / HB = 17.5%), and long ears (average E = 19.1 mm, E/ GLS = 56.3%). Ventral coloration is paler than the dorsum, with buff-tipped, dark-grey hairs. Brown-yellowish hue in the throat area is generally inconspicuous and just present in females (but these could be due to phenological sampling biases: specimen series collected in April). All specimens have an ochraceous hue around the cloaca/inguinal area. Fore/hindfeet and tail have a lighter and darker coloration than dorsum, respectively. The skull of this species is distinguished from all other congeneric species by a unique combination of the following characters: acute-angled notch between premaxilla tips; long nasals; narrow rostrum; poorly developed antorbital ridge/flange; broad interorbital constriction; small but prominent supraorbital process in males, which is generally inconspicuous in females; relatively smooth frontal bone and dorsal region of maxillary; anterior palatine foramina (generally) anterior or (rarely) at level of maxilla/palatine suture; generally thick and robust postpalatine torus; lack of posterior nasal spine; elongated pterygoid process; robust and globular ectotympanic process that tappers dorsoventrally towards proximal end; gracile mandible, with relatively short vertical height at coronoid and length of angular process; procumbent incisors; single root in P2; P2 and P3 lack posterior cuspules, even in subadults and young specimens; absent labial cingulum in P4; anterior margin of p1 crown does not extend to root of c1; p3 is much larger than p2 and larger than p1, p1 is generally larger than p2; posterior cuspule of p2 absent, even in subadults and young specimens; single root in p3.

Comparisons: Compared with its closest geographical and genetic relative, Hylomys maxi , H. vorax is distinguished by its smaller (average HB = 123 mm; W = 44.4 g; GLS = 34.5 mm; LMA = 24 mm; Fig. 9A ) vs. larger size ( HB = 139 mm; W = 64.2 g; GLS = 36.9 mm; LMA = 26.3 mm; Fig. 9B ), uniformly black and relatively longer (average T = 21.4 mm, T / HB = 17.1–18.8%) vs. bicoloured (except specimen RMNH 23896) and relatively shorter tail (average T = 16.2 mm, T / HB = 5.11–16.9%) (Supporting Information, File S1, Fig. S10A ), and a relatively longer (E/ GLS = 54.8–55.9%) vs. shorter ear (E/ GLS = 39.3–48.2%) (Supporting Information, File S1, Fig. S10B ). Its fur is softer, denser, and longer (7–8 mm at axial region) than H. maxi (4–5 mm at axial region), although higher elevation (> 1100 m a.s.l.) Sumatran H. maxi specimen furs were not measured, and this trait is subject to great ecophenotypic variation in this genus ( Ruedi et al. 1994).

The skull of H. vorax has a narrower and more gracile appearance than H. maxi . The notch between the premaxilla tips is acute vs. obtuse in H. maxi ( Fig. 10 ). Its rostrum breadth is narrower (4.5–5.0 mm) vs. broader (5.2–6.4 mm) in H. maxi . Its nasals are relatively longer (average NL / GLS = 36.1%) vs. shorter in H. maxi (average NL / GLS = 32.4%; Supporting Information, File S1, Fig. S10C ). Antorbital ridge/flange is undeveloped vs. well developed in H. maxi , particularly between the lacrimal flange and supraorbital process. Its frontal bone and dorsal region of maxillary has a relatively smooth vs. rugged appearance in H. maxi . Its interorbital constriction is proportionately broader than H. maxi (Supporting Information, File S1, Fig. S10D ). Zygomata and supraorbital processes are less robust than in H. maxi . Anterior palatine foramina end anteriorly or (rarely) at maxilla/palatine suture vs. posterior to maxilla/palatine suture in H. maxi . Postpalatine torus is generally thicker and more robust than in H. maxi . Posterior nasal spine is absent vs. present in H. maxi . Postpalatal length is shorter (11.1–12.3 mm) vs. longer (12.3–14.2 mm) in H. maxi , while braincase is similar in breadth (average BB = 14.8 vs. 15 mm). Epipterygoid processes are lateroventrally vs. lateral oriented in H. maxi . Its robust ectotympanic process thickens dorsoventrally towards the tip, while it is more gracile and dorsoventrally flattened in H. maxi ( Fig. 10B ). Occipital crest absent or inconspicuous and shorter vs. prominent and longer in H. maxi . Its mandible is more gracile, with a shorter vertical height at coronoid and shorter length of angular process ( HCO = 7.4–8.6 mm; LAP = 7.9–9.1 mm) than H. maxi ( HCO = 8.6–10.7 mm; LAP = 8.8–10.8 mm).

Its dentition appearance is less robust than that of H. maxi , with smaller teeth and more space between incisors, canine, and premolars than H. maxi . I1 is more procumbent than H. maxi . P1 is usually similar in size to P3 vs. generally much larger in H. maxi . P4 labial cingulum absent or inconspicuous vs. well developed in H. maxi . Molars are smaller (M1M1 = 9.8–10.8 mm; P4M3 = 7.5–8.2 mm) vs. larger (M1M1 = 10.9–12.5 mm; P4M3 = 8.3–9.9 mm) in H. maxi . Its lower toothrow is shorter (16.6–17.7 mm) vs. longer (17.6–18.9 mm) in H. maxi . Crown height of c1 is generally greater in H. vorax than H. maxi , the latter species c1 is more expanded anteriorly, giving it a less prominent appearance. Anterior margin of p1 crown does not extend anteriorly to the root of c1, but it does in H. maxi . p3 is usually much larger than p 2 in H. vorax , while it has a similar size or p3 is just slightly larger than p 2 in H. maxi .

Distinguished from H. parvus by its larger size ( HB = 117– 128 mm; GLS = 33.4–36.3 mm; LMA = 23–25.6 mm vs. HB = 100–115 mm; GLS = 29.2–33.4 mm; LMA = 20.1–22.2 mm) and black monocoloured and relatively shorter (average T / HB = 17.5%) vs. bicoloured and relatively longer tail (average T / HB = 22.4%). Rostrum is longer ( ROL = 15.2–17.3 vs. 13.6–15.0 mm) but similar in width ( ROB = 4.52–5.05 vs. 4.43–5 mm) to H. parvus , giving H. vorax a more elongated appearance. Toothrow length is longer ( IM 3Sa = 17.2–18.5 mm; IM 3I = 16.6–17.7 mm) than in H. parvus ( IM 3Sa = 16.1 mm; IM 3I = 14.5–16 mm). Braincase and palate breadth are wider in H. vorax ( BB = 14.5–15.1 mm; M3B = 6.1–6.4 mm) than H. parvus ( BB = 13.1–14 mm; M3B = 4.7–6 mm). Height of the coronoid process is proportionately shorter than H. parvus (Supporting Information, File S1, Fig. S10E ). First upper incisor is more procumbent than H. parvus . Males have small but prominent supraorbital processes, which are absent in H. parvus . It has a single root in P2 and p3 vs. two non-fused roots in H. parvus ( Jenkins and Robinson 2002) .

Distribution, habitat, and natural history: Currently known from montane forest from 2073 to 2835 m a.s.l. on Mount Leuser, but it seems to be most abundant at elevations ranging from 2073 to 2408 m a.s.l. ( Fig. 11 ). This habitat is characterized by ‘trees averaging only 15 to 40 feet in height, very hard, knotted and twisted. Everywhere the ground and the branches of the trees were covered with a deep carpet of moss and ferns’ (Ulmer’s field notes, Miller 1942). However, one specimen was recorded at 2835 m a.s.l., described as ‘flat heathy plateau mostly bare or covered with grass interspersed with patches of bushes and low trees’ such as ‘rhododendrons, Vaccinium , and Quercus ’ (Ulmer’s field notes, de Schauensee and Ripley 1939). Its lower elevational limit is unknown, but possibly around 2000 m since there is a noticeable change from moss forest to foothill jungle according to Miller (1942). Furthermore, the lower elevational limits of H. vorax might be constrained by H. maxi , which has been recorded between less than 100 and 1100 m a.s.l. in Aceh, and up to 2200 m a.s.l. on Mt. Kerinci. We suggest H. maxi and H. vorax have a parapatric distribution in the Gayo Highlands mirroring the elevational segregation of H. maxi and H. parvus on Mt. Kerinci ( Ruedi et al. 1994). Additional sampling at Gayo Highlands between 1100 and 2000 m a.s.l. will be required to confirm this hypothesis. Hylomys vorax seems to show preference for moist microhabitats with high cover, since six over nine specimens with associated habitat field notes were caught in a mossy area next to a river. These specimens were caught either under mossy logs (N = 4), under tree roots in thick scrubby jungle (N = 2), in thick growth near blang (=meadow) (N = 1), mossy hole at base of tree (N = 1), or in grass in an open glade near forest (N = 1). Stomachs contained the chewed remains of earthworms (N = 2), and specimens were caught with ham rind or coconut bait (Ulmer’s field notes). A subadult male and two females were caught under the same log. The most likely scenario is that a mature female with teats ( USNM 271033) and its offspring (subadults ANSP 20375 and 20378) were collected together, perhaps suggesting parental care and/or territory overlap with offspring at least until adulthood. Three adult specimens had a very strong porcine odour, but this was not mentioned for any of the subadults in Fred Ulmer’s field notes. It shares habitat with Maxomys hylomyoides ( Robinson and Kloss 1916) , Rattus hoogerwerfi (Chasen 1939) , Sundamys infraluteus (Thomas 1888) , and Sundasciurus altitudinis ( Miller 1942) .

Conservation: This species is found in Gunung Leuser National Park ( GLNP). The Leuser ecosystem is designated as a ‘national strategic area’ ( NSA) in Indonesia, to safeguard ecosystem services and limit infrastructure and agricultural expansion for ecological preservation. However, recent actions by the Aceh provincial government, which omitted Leuser’s NSA status and proposed conflicting development projects, have created uncertainty about its conservation status and the effectiveness of decentralized forest governance in Indonesia ( Sloan et al. 2018). GLNP has lost c. 8000 ha of its primary forest from 2012 to 2017, possibly due to a combination of industrial oil palm plantations, dryland agriculture, and forest fires ( Lubis et al. 2020, Condro et al. 2021, Dwiyahreni et al. 2021, Thoha et al. 2022). The Leuser Ecosystem is also threatened by habitat fragmentation due to unofficial road development and conversion of ‘sustainable managed’ buffer forests to palm oil plantations ( Sloan et al. 2018). While most deforestation is taking place in lowland areas, it is suggested that the magnitude of climate change effects will be higher on the montane areas of the GLNP ( Condro et al. 2021). Finally, it is anticipated that the Trans-Sumatra Highway’s completion, if constructed according to the current plan, would encourage increased anthropogenic pressure on the outskirts of the GLNP, potentially impacting its fragile ecosystem ( Sloan et al. 2019). Species co-distributed with H. vorax , like Rattus hoogerwerfi and Presbytis thomasi , have similar or larger occurrence ranges and are listed as vulnerable in the IUCN Red List of Threatened Species. Further research is required to assess H. vorax population trends, explore its distribution beyond Mt. Leuser, and investigate whether H. maxi is displacing H. vorax due to climate-induced elevational changes.

Comments: Five specimens ( MZB 3172–5, RMNH 5137-8) with damaged skulls collected in Pajatoeng Kalang (south of Isaq) at 2000 m were clustered in the morphospace of H. vorax in some preliminary uni/bivariate analyses ( MZB 3172–5: HB/E, GLS / IM 3Sb, M1M1, IM 3I; RMNH 5137-8: HB/E, P4M3) but in between H. maxi and H. vorax ( MZB 3172–5: HB/ T, GLS / BB; RMNH 5137-8: M1M1, IM 3I) or in the range of H. maxi in others ( RMNH 5137: T, PPL). Specimens RMNH 5137-8 skins and skulls were examined through pictures and have a bicoloured tail ( H. maxi feature), but most cranial or mandible features were consistent with H. vorax . These were excluded from Table 1 and all bivariate plot figures since they were collected in a habitat transition and potentially parapatric (and perhaps even hybridization) area of H. maxi and H. vorax , and were not sequenced nor included in the craniodental PCA due to their damaged state. Lastly, diagnostic measurements of RMNH 5137-8 were not collected by the authors, but by Pepijn Kamminga (senior collection manager at RMNH) and could be subject to observer bias.

Figures

Figure 9. Skulls of (A) Hylomys oorax (USNM 271034, holotype) and (B) Hylomys maxi (USNM 487905, standard specimen since holotype is damaged). All images are at the same scale. Photo credits: Katie Sayers.

Figure 10. A, dorsal view of the rostrum of two H.oorax specimens (left; ANSP 20374 and 20377) and two H. maxi specimens from Sumatra (right; ANSP 20372 and ZRC4.5051), which illustrates the narrow, notched space between premaxillary tips of H.oorax (vs. broad/obtuse in H. maxi). B, lateral view of the bullae of H. oorax (left; ANSP 20377) and H. maxi (right; USNM487909), which illustrates the robust ectotympanic process that thickens distally in H. oorax (vs. more gracile and dorsoventrally flattened in H. maxi).

Figure 11. A, trapline set by Frederick A. Ulmer and other collectors of the George Vanderbilt Expedition. B, habitat of H. oorax in Blangbeke (2073 m a.s.l.), Aceh, Sumatra.C, habitat of H.oorax, view from the summit of Gunung Leuser looking eastward.D, paratype of Hylomys oorax (ANSP20377) collected on 12 April 1939 by Fred Ulmer in Blangbeke, Aceh, Sumatra, and illustrated by him (Supporting Information, Fig. S11). Picture credits:ANSP Archives Collection (unaccessioned Vertebrate Zoology 2012-01: George Vanderbilt Sumatra Expedition in 1939: photographs and images by Frederick A. Ulmer, Jr).