Hylomyscus pygmaeus, Kerbis Peterhans & Hutterer & Doty & Malekani & Moyer & Krásová & Bryja & Banasiak & Demos, 2020
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publication ID |
https://doi.org/10.20363/BZB-2020.69.1.055 |
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publication LSID |
lsid:zoobank.org:pub:1FD4D09C-D160-4159-A50D-20B6FBC7D9E9 |
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persistent identifier |
https://treatment.plazi.org/id/C54F87EA-FFBE-FFD0-6316-F9D3FF7CF993 |
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treatment provided by |
Felipe |
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scientific name |
Hylomyscus pygmaeus |
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sp. nov. |
Hylomyscus pygmaeus sp. nov. Kerbis Peterhans, Hutterer & Demos
urn:lsid:zoobank.org:act:1B7A9BDE-24A0-47DE-9B66-F3B40D95EE54 Dendromus sp. – Doty et al. (2017)
Holotype. Field Museum of Natural History , Division of Mammals number FMNH 219684 About FMNH (field number WT Stanley 11,575; CDC 207 ), collected by W. T. Stanley, 13 June 2012 (listed in field notes as Dendromus sp. ) during the first small mammal survey in the area. The specimen, consisting of a study skin and skull with carcass in alcohol, is a young adult female with first upper molar in early wear (stage IV of Verheyen & Bracke 1966). The basisphenoid-occipital suture is unfused. External mea-
Taxon 1 2 3 4 5 6 7 8 1 anselli 2 arcimontensis 1.1 8.1 1.5 3 mpungamachagorum sp. nov. 8.2 6.0 0.0 4 heinrichorum 4.4 7.9 8.4 0.3 5 kerbispeterhansi 8.1 6.6 4.7 8.0 0.0 6 stanleyi sp. nov. 8.2 6.3 4.9 9.3 3.2 0.0
8 pygmaeus sp. nov. 11.1 10.9 10.9 10.9 10.8 11.5 12.1 na
surements were made in the field: TL 132, TV 76, HF 14, EL 12, Wt 5.8. Specimen caught in a pitfall trap ( PF 4, Bucket 10).
Type locality. Democratic Republic of Congo, Tshuapa Province , 4 km N of Boende, Baliko (0.24127 S, 20.8833 E), right side Tshuapa River, elevation of 358 m. GoogleMaps
62 Julian C. Kerbis Peterhans et al.
Diagnosis. Easily recognized by its small size: HB 56, Wt 5.8, CI 15.9, CLM 2.6, WM1 0.8. All are signifi- cantly smaller than any other members of the H. anselli group ( Figs 5a, c View Fig , 6a, c, e View Fig ; Tables 4–5), or, for that matter, any member of Hylomyscus . Ears exceptionally long ( Fig. 5c View Fig ), 23% of HB. Incisors slightly pro-odont ( Fig. 6e View Fig ). Braincase inflated, round and bulbous ( Figs 6a, e View Fig ). Rostrum extremely short ( Fig. 6a View Fig , LN/ONL = 26.7%).
Comparisons. This species is by far the smallest member of the Hylomyscus anselli group as reflected in Ta- bles 4–5: e.g., crown length of upper molars 2.6, compared to 3.0–4.5; HB 56, compared to 76–109 for other members of the group.
Description. Size very small (HB 56, mass 5.8). Tail 36% longer than HB. Tail unicolor with 21–23 annulations per cm. Ears long, 23% of HB, 13 mm re-measured from dry study skin (vis a vis field notes = 12 mm). Bel- ly hairs 3 mm, basal 50% slate grey, distal 50% slightly ochraceous. Dorsal hairs 4 mm, basal 2.5 mm slate grey, tipped with carmel brown. Dorsum of head appearing more grey, due to shorter ochraceous tips (perhaps in molt). Upper lip creamy white. Vibrissae ‘long’ – up to 25 mm in length –, ventral vibrissae white; dorsal vibrissae black and shorter. Young adult female with mammae not visible on dry skin. The number of fleshy pads on the hind foot are not determinable from the single study skin. The number of fleshy palatal ridges are not visible in the single cleaned skull.
Skull tiny (ONL 17.45, CRM 2.6). Rostrum exceptionally short (LN/ONL = 26.7%) but this is expected to increase in older individuals. Inter-orbital region proportionately broad. Upper incisors slightly pro-odont. Incisive foramina fall short of upper tooth row. T3 on M 2 is present but a tiny vestige. Braincase bulbous and dorso-ventrally inflated. Hamular process of the squamosal long and thin, providing for a very large subsquamosal fenestra which is about 40% the size of the postglenoid foramen (see Carleton & Stanley 2005: fig. 6). Maxillo-pal- atal suture located at the rear third of the M 1 ( Figs 6c View Fig , 8a View Fig ). Post palatal foramina large, starting between M 1 and M 2 and extend back to middle of M 2 ( Figs 6c View Fig , 8a View Fig ). Fronto-parietal suture broadly U-shaped. Zygomatic plate narrow (1.34 mm) and without any sinuosity but gently sloping forward throughout. Mesopterygoid fossa rounded and open widely at rostral end.
As a divergent member of the Hylomyscus anselli group, some of the following characters contrast the Carleton et al. list of characters (2006: table 7) defining this group: 1) pectoral mammae unknown (not available as the holotype is a young adult), 2) upper incisors slightly pro-odont ( Fig. 6e View Fig ), whereas Carleton et al. (2006) characterized the H. anselli group as opisthodont, 3) T3 on M 1 is distinct and sub equal with t1 rendering it ‘large’ per Carleton et al. (2006); the anterior chevron is more or less symmetrical ( Fig. 7g View Fig ), whereas Carleton et al. (2006) characterized the ‘ H. anselli ’ group as having a ‘medium’ sized t3 (e.g., smaller than t1), 4) t9 on M 1 is distinct ( Fig. 7g View Fig ),whereas Carleton et al. (2006) characterized the ‘ H. anselli ’ group as ‘indistinct’ 5) interorbital constriction is amphoral, whereas Carleton et al. (2006) characterized the ‘ H. anselli ’ group as having a ‘weak shelf, 6) rostral length is extremely short ( Fig. 6a View Fig ), whereas Carleton et al. (2006) characterized the ‘ H. anselli ’ group with a ‘medium’ length rostrum, 7) incisive foramen is short, falling well short of the alveoli of M 1 ( Figs 6c View Fig , 8a View Fig ) as opposed to the Carleton et al. (2006) characterization as ‘medium’ (reaching anterior root of M 1), 8) the hamular strap is long and thin, subsquamosal foramen is large in size (see Carleton & Stanley 2005: fig. 6; Fig. 6e View Fig ). In sum, several characters of this new species are unique or align more with the Hylomyscus alleni group than the H. anselli group: more proodont, distinct T9 on M 1, amphoral inter-orbital region, extreme shortening of the rostrum, and shorter incisive foramina. Perhaps these contrasts are not surprising given the basal position of this taxon.
Ecology. The habitat is seasonally flooded primary for- est, ‘edaphic forest’ (Verhegghen et al. 2012). However, the pitfall line was set in a drier part of the forest and was less subject to flooding. The area supports two dry seasons (January to early March, and June to early September) with the rest being rainy averaging ca. 210 cm per year. Daily temperature average between 24 °C and 30°C ( Doty et al. 2017). Type specimen was caught in a generally dry area of the forest.
The vegetation of the Tshuapa region is mainly characterized by sempervirent or semi-sempervirent rain forests bound to hydromorphic soils, secondary forests and grassy vegetation ( Evrard 1968). The sempervirent rain forests of terra-firma are distinguished by their struc- tural density, distinct stratification and epiphytism (Leb- run & Gilbert 1954), while the upper stratum can reach 40–45 m in height. There are two types of forest bound to hydromorphic soils in swampy zones. These include periodically flooded forests (including where the type spec- imen was collected) comprising the following species: Parinari congolensis, Guibourtia demeusei, Zeyrrhella longipedisellata and swampy forests composed of Entandrophragma palustre , Alstonia congolensis , Coelocaryon botryodes , and Sterculia tragacantha . The second forest type is composed of bushy forests along the banks of large rivers including Alchornea cardifolia, Lacosperma secundiflorum; waterside forests with Coelocaryon botryodes , Erispermum microspermum, Sclerosperma manirii, and Cleistanthus mycrophyllus . Secondary forests are found around villages, roads and on former sites of forest extraction. Species frequently observed are Musanga cecropioides , Harungana madagascariensis , Trema orientalis, Oncoba subtomentosa, Pycnanthus angolensis , Petersianthus macrocarpus, Ricinodendron heudelotii, Canarium schweinfurthii, Alstonia boonei, and Elaeis guineensis . Grassy vegetation results from forest degradation and includes frequently burnt fallow fields, mainly with Graminaceae of the genera Panicum, Pennisetum, Imperata, Serata , and Sorghum ( Evrard 1968) .
Reproduction. The sole specimen is a young female with teats that are neither developed nor visible.
Four new Hylomyscus ( Muridae ) from Africa 65
Etymology. Named for its diminutive size. We recommend “pygmy wood mouse” as an English common name.
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Tavera, Department of Geology and Geophysics |
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Centro de Estratigrafia e Paleobiologia da Universidade Nova de Lisboa |
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