Malaysian bearded pigs
C. Boden Kloss, a zoologist affiliated with the Raffles Museum in Singapore, published this taxonomic study in 1921 examining the systematic relationships among bearded pig species (Sus barbatus, Sus oi, and Sus gargantua) from Borneo and Sumatra. Working from a small series of skulls and mandibles, Kloss challenges the previously accepted sharp species-level distinction between the Bornean and Sumatran bearded pigs, arguing instead for a subspecific relationship grounded in subtle cranial metrics rather than molar morphology alone.
Summary
The article addresses a persistent taxonomic problem in Malayan suid classification: whether the Sumatran bearded pig (Sus oi) constitutes a full species distinct from the Bornean Sus barbatus, or whether the differences between them are insufficient to warrant that rank. Miller’s earlier work had established the distinction primarily on the morphology of the third lower molar—three cross ridges with a terminal heel in barbatus versus two cross ridges in oi—but Kloss demonstrates that three of his six Bornean specimens exhibit the supposedly Sumatran molar pattern, undermining the diagnostic reliability of that character (pp. 148–149).
Kloss therefore turns to cranial measurements and shape to propose a more defensible basis for separation. The Sumatran animal shows a longer muzzle, longer mandibular symphysis, slightly deeper mandible, a somewhat more concave facial profile, and greater overall skull size. On this basis he recommends maintaining the Sumatran form as a subspecies, S. b. oi, rather than a full species (p. 149).
The article also takes up the enigmatic Sus gargantua, a single very large skull from south-eastern Borneo whose molars are indistinguishable from those of barbatus and oi but whose cranium is markedly larger and differently shaped. Kloss leaves its taxonomic status open—possibly an abnormal barbatus or a distinct species—while noting that Malay informants in eastern Sumatra describe a similarly large pig (“Babi branti”), suggesting a parallel Sumatran form (pp. 149–150).
Key Findings
- Three of six Bornean S. barbatus specimens in Kloss’s series display the molar pattern previously considered diagnostic of S. oi, demonstrating that molar morphology is not a reliable species-level character (p. 148).
- Maximum upper skull length in Kloss’s series: 480 mm for barbatus versus 520 mm for oi (Tanjong Batu, Rio Archipelago); the USNM series gives 487 mm and 505 mm respectively (p. 149).
- Sus gargantua (type from SE Borneo) measures 570 mm in upper skull length—substantially larger than either barbatus or oi—yet its molars show no distinguishing features (p. 149).
- The Sumatran subspecies is distinguished by a longer muzzle (front of premaxilla to anterior canine alveolus), longer mandibular symphysis, slightly deeper mandible, and a more concave facial profile (p. 149).
- Kloss’s Bornean material comprises five adult skulls with mandibles and one mandible from the southern half of Sarawak; his Sumatran set includes a topotype of S. oi and three additional specimens from Tanjong Batu, south-east of Great Durian Island, Rio Archipelago (p. 148).
- Kloss concludes that only three real species of pig exist in the Malayan sub-region (excluding the Philippines and Celebes): Sus scrofa (encompassing S. cristatus, S. vittatus, and all common wild swine forms), Sus barbatus (including S. b. oi), and Sus verrucosus of Java (p. 150).
Conclusion
Kloss’s definitive takeaway is that the bearded pig of Borneo and Sumatra represents a single species with a Sumatran subspecies, and that the molar-based distinction erected by Miller is too variable to sustain specific rank. He further identifies Sus gargantua as a taxonomic problem of unresolved status—potentially a fourth species in the region—whose existence is corroborated by indigenous reports of a large pig in eastern Sumatra, and he calls for the preservation of complete specimens to resolve the question.
Context
- The study draws on material from the Raffles Museum, Singapore (the Sumatran series was lent by that institution), and references the US National Museum collection in Washington (p. 148, footnote 2).
- The article contributes to the early twentieth-century effort to stabilise the taxonomy of Malayan mammals, building directly on Miller’s 1905 monograph and Lyon’s 1908 revision, and reflects the standard practice of the period in which a single individual’s small series could prompt a re-evaluation of species boundaries.