On some Carnivora, Rodentia and Insectivora principally from Eastern Borneo
Chasen and Kloss (1928) present a taxonomic determination of mammalian specimens collected by ornithologist H. C. Siebers during the 1925 Middle-East Borneo Expedition, describing two new pygmy squirrel subspecies and revising the nomenclature of several Bornean carnivores, rodents, and insectivores. The work draws on material from the Telen River drainage in the Samarinda division, extending from Tenggarong at sea level to Punt D at 1,172 metres, supplemented by a few specimens from the Melawi River in Western Borneo.
Summary
The paper addresses a gap in mammalian knowledge of Eastern Borneo, a region previously worked only sporadically by Lumholtz (1914–1915) on the Boelongan River and Abbott (1908–1909) south of Balik Papan Bay. Although Siebers was primarily an ornithologist, his mammal collection proved taxonomically productive, yielding material that prompted the authors to name two new subspecies of Nannosciurus—N. melanotus pallidus and N. exilis sordidus—both distinguished from their western counterparts by duller, greyer upperparts and reduced rufous suffusion (p. 37).
A significant portion of the paper is devoted to resolving nomenclatural confusion in Bornean mammals. For the palm civet, Chasen and Kloss argue against recognising two size-based races (sabanus and baritensis) in Borneo, contending that Viverrids show too much individual variation in size for dimensional subspecies to be reliably proposed on small samples (p. 39). Similarly, for the short-tailed mongoose, they reject Thomas’s distinction between a lowland rajah and a mountain dyacorum, attributing the rufous appearance of old dyacorum skins to deterioration rather than genuine colour difference, and adopt rajah as the prior name for all Bornean forms (p. 40).
The rodent section is the most extensive, covering squirrels, rats, and a shrew-mouse. The authors note that Sciurus notatus dilitensis from the east of Borneo is consistently paler below than western specimens, and that Sciurus tenuis jentinki represents a distinct altitudinal form occurring at 1,172 metres at Long Petak (p. 42). Among rats, they confirm Rattus surifer bandahara from Kina Balu in the Telen drainage and identify Rattus argentiventer from a single specimen at Moeara Antjaloeng, noting its diagnostic cranial features despite a damaged skull (p. 47). The insectivore section records a range extension of Tupaia glis salatana northward to the Melawi River (p. 48).
Key Findings
- Two new subspecies described: Nannosciurus melanotus pallidus (type: adult male, Long Poehoes, 10 August 1925, Buitenzorg Museum No. 1178; condylo-basilar length 21 mm) and N. exilis sordidus (type: adult female, Long Temelan, 26 August 1925, Buitenzorg Museum No. 1189; condylo-basilar length 19 mm) (pp. 43–44).
- Sciurus tenuis jentinki recorded from Punt D at 1,172 metres, the highest altitude yet documented for this altitudinal form, which co-occurs with S. brookei at the same locality (p. 42).
- Rattus argentiventer confirmed from Moeara Antjaloeng, Eastern Borneo, with tail shorter than head and body (174:157 mm in the flesh) and hindfoot 34 mm, distinguishing it from the rattus group by longer toothrow, larger bullae, and broader infraorbital plate (p. 47).
- Tupaia glis salatana extended northward to Lebong Hara, Melawi River, Western Borneo, beyond its previously known range along the south coast from Pangkallahan to Kendawangen (p. 48).
- The authors reject Nannosciurus exilis as a Sumatran species, reassigning the type locality to the Kapuas River basin in Western Borneo on the grounds that no reliable record exists from Sumatra and the species’ presence in the Sulu and Philippine groups makes a southwestern Malaysian origin improbable (p. 44).
- A single Chiropodomys specimen from Long Petak is noted as distinct from all described Bornean forms in having fawn-coloured underparts rather than white, but no new name is proposed given the single example (p. 48).
Conclusion
Chasen and Kloss demonstrate that even a collection assembled incidentally by an ornithologist can yield significant taxonomic results for a poorly known region. Their conservative approach—declining to erect new names on single specimens or to accept size-based subspecies in highly variable groups—reflects a methodological caution that was becoming standard in interwar mammalogy, while their two new pygmy squirrel subspecies remain valid contributions to the biogeography of Bornean small mammals.
Context
- The primary material derives from the Buitenzorg (now Bogor) Zoological Museum collection, with determinations made at the Raffles Museum, Singapore; the authors also consulted comparative series from Sarawak and the Malay Peninsula held in their own collections.
- The paper sits within the broader programme of the Indisch Comite voor Wetenschappelijke Onderzoekingen, whose 1925 Middle-East Borneo Expedition was published in 1927, and represents one of the first systematic mammalogical treatments of the Mahakam–Telen drainage system.