Tragulus napu

Meijaard, E. & Groves, C. P., 2004, A taxonomic revision of the Tragulus mouse-deer (Artiodactyla), Zoological Journal of the Linnean Society 140 (1), pp. 63-102 : 70-75

DIFFERENCES WITHIN T. NAPU

Based on the outcome of a principal component analysis of the T. napu skull measurements, we grouped the specimens into four geographical units: (1) Terutau and Langkawi Islands; (2) Borneo, Sumatra, the Malay peninsula, and mainland Asia; (3) islands offshore from the areas in group 2 but excluding those in group 1; and (4) the isolated T. napu versicolor population in SE Vietnam (note that T. napu does not occur on Java). A discriminant analysis of the adult specimens in these groups resulted in a 90% correct classification of the originally grouped cases. When young adult–adult specimens were added, the classification accuracy dropped to 85.9%, but there was still a clear separation between the four groups ( Fig. 5). The SE Vietnam group is distinct from the others as no specimens from this group were embedded in any of the other groups. In addition to this, it was noted that specimens from Balabac, an island south-west of the Philippine island of Palawan, grouped closely together, although they were still embedded in the group of Borneo, Sumatra, and Malaya specimens.

The skulls from Borneo, Sumatra, the Malay peninsula, and mainland Asia have the highest mean values for all the measurements (‘Mainland and main islands’ in Table 2). The SE Vietnam specimens were primarily distinguished by their overall small size, and a high value for function 3 (not shown here), which correlated with a relatively wide braincase and condyles. The Terutau and Langkawi specimens were characterized by a low value for function 2, which mostly correlates with relatively long, narrow auditory bullae, a relatively wide skull, i.e. high values for ZW, CW, and WB, and relatively high values for OHO and OHB (see Table 2). The two groups consisting of specimens from Borneo, Sumatra, and Malaya, and small Sundashelf islands specimens partly overlap.

Variation within the Borneo, Sumatra, Malay peninsula, and Asian mainland groups

A discriminant analysis within the Borneo, Sumatra, Malay peninsula, and Asian mainland geographical groups could not meaningfully distinguish between them. Furthermore, an ANOVA between the nominate form from Sumatra and specimens from Borneo did not result in statistically significant differences between the groups, nor did the same test between Sumatran and Malayan / Thai / Burmese specimens. The means and standard deviations for these groups are provided in Table 3. There was some differentiation between skin patterns from the different regions (we were unable to study any skins from Sumatra), but because the series from each of the regions were too small it remained unclear how the interregional variation related to the observed intraregional variation .

One specimen (ZRC 4.4731), a juvenile from Pangkor Island (2 km off the west coast of the Malay peninsula), had skin coloration patterns similar to T. napu from the Malay peninsula, with black streaked, yellowish-brown upperparts, dark nape streak, and a normal throat pattern.

Borneo and adjacent islands. An initial analysis of the means of T. napu measurements of specimens from Borneo and nearby islands showed that specimens of T. n. nigricans (N = 7) from the Philippine island of Balabac, north of Borneo, were significantly smaller than any of the other specimens. This raised the possibility that the classification of this subspecies as T. napu was wrong, and that it should have been classified as a member of the T. javanicus / kanchil group instead. A discriminant analysis using five skull measurements of young adult, young adult–adult, and adult specimens from Balabac, and of specimens of the T. javanicus / kanchil and T. napu groups from Borneo, however, showed that the three groups are completely separated ( Fig. 6). Balabac specimens were of intermediate length and they were differentiated from the two other groups by low values for WB, CW, OHB, BW, and BL (low BL also translated into a relatively high IB) (see Table 4). Because there were few differences within the Borneo/ Sumatra /Malaya group of T. napu specimens (see above), and they will probably form one subspecies, we also compared the Balabac specimens to all specimens from this larger group. The two groups were separated in a discriminant analysis with 95% accuracy using the measurements for BPL, ML, ZW, CW, and OHB. An ANOVA showed that the Balabac specimens were significantly smaller (P <0.01) for CBL, BPL, ML, ZW, CW, OHB, and WB. We found similar results for a comparison between the Balabac specimens and the joined groups of Borneo, Sumatra, and Malaya, and the small Sundashelf islands (minus Bunguran) specimens.

Specimens from Banggi, another island off northern Borneo, also differed from the rest of the Bornean specimens. We only measured two specimens from this island, of which one was juvenile, and we were unable to study any skins. The measurements of the adult specimen suggested that the island taxon is considerably smaller than that from the mainland, but clearly our sample size was very small. Because Chasen & Kloss (1931) suggested that the Banggi Island specimens were very near to both T. nigricans from Balabac and T. napu borneanus , we compared the Balabac and Banggi specimens with the nominate subspecies T. n. napu to investigate the relationships further. The results were inconclusive, largely because we only measured one Banggi specimen, with additional measurements for two specimens from the literature.

T. napu (Borneo)

Balabac specimens

T. javanicus

(Borneo) When we compared the Banggi specimen with T. n. nigricans , T. napu from Borneo, and the T. javanicus / kanchil group from Borneo, it grouped with the latter ( Fig. 6), which suggests that it may initially have been misclassified, and that it should instead be classified as belonging to the T. javanicus / kanchil group.

Within Borneo the size of T. napu skulls varied considerably. The smallest specimens originated from Sarawak, the largest from Sabah and East Kalimantan, and intermediately sized specimens from West and Central Kalimantan ( Table 5). There were no skin descriptions or photographs available to check whether these differences in skull dimension translated into similar groupings of skin patterns.

Sumatra and west Sumatran islands. Two subspecies of T. napu have been described for mainland Sumatra, the nominate subspecies T. napu napu E. Geoffrey & F. Cuvier, 1822 , which Sody (1931) restricted to South Sumatra, and T. n. neubronneri Sody, 1931, from Aceh, northern Sumatra. Furthermore, several subspecies were described for islands off the west coast of Sumatra, including amoenus and jugularis ( Miller, 1903b) from Mansalar (= Musala) Island, batuanus ( Miller, 1903c) from Tana Bala Island, and niasis ( Lyon, 1916) from Nias Island. The subspecies from the islands off the east coast of Sumatra are analysed in the next section.

Within Sumatra, we compared specimens from north (N = 7) and south (N = 6) of Lake Toba, the main faunal break in Sumatra ( Whitten et al., 2000). Similar to what Sody (1931) reported, the northern specimens were larger than those from the south, although none of the differences was significant when tested in an ANOVA. The one specimen from Nias in this research, an adult female, was slightly smaller than the mean values for the northern mainland population, and had a relatively narrow skull (low values for ZW, CW, and WB). Neither a principal component analysis nor a bivariate analysis could significantly separate the Nias specimen from the nominate T. napu from Sumatra. Miller (1903b) provided measurements for two specimens from Musala (which he assigned to different species); again these were slightly smaller than those from the mainland although larger than the Nias specimen.

Variation within the Terutau/Langkawi group

To explore the difference between the Terutau specimens and the adjacent group from Borneo, Sumatra, Malay Peninsula, and Asian mainland we compared these without the inclusion of the small Sundaland islands specimens. The two groups were classified with 92.5% accuracy in a discriminant analysis, which means that in that analysis 92.5% of the cases were classified to belong to their original group, the rest having a higher probability of belonging to another group. Furthermore, we conducted three ANOVAs: Terutau/Langkawi vs. the combined Borneo, Sumatra, Malaya, and small Sundaland islands groups (minus Bunguran); Terutau/Langkawi vs. the Borneo, Sumatra, and Malaya group; and Terutau/Langkawi vs. specimens from the adjacent Malay peninsula. All three ANOVAs resulted in significant differences (P <0.01) for CW, OHB, OHO (only the first two tests), BW, and IB (only for the last two tests).

Two subspecies of T. napu have been described from these islands, T. canescens terutus Thomas & Wroughton, 1909 , from Terutau, and T. canescens umbrinus Miller, 1900 , from Langkawi. The main difference between the two subspecies, according to Thomas & Wroughton (1909), was the dark-coloured nape, considered characteristic of umbrinus, which was completely absent in the seven specimens of terutus that they investigated. The two terutus skins studied in this research (ZRC 4.4724, 4.4784), however, both had a black stripe in the neck, which connected to a black patch on top of the head. We did not study any skins from Langkawi. We measured one adult skull from Langkawi (BNHM 9.11.1.166) and 12 from Terutau (11 adults, one young adult), and a comparison of skull dimensions showed a major difference. For five of the seven measurements, values for the Langkawi specimen were completely outside the range of the maxima for the Terutau specimens. For instance, CBL for the Langkawi specimen was 108.4 mm, whereas that for the Terutau specimens (N = 9) ranged from 97.1 to 102.1. The Terutau specimens were overall considerably smaller than the Langkawi specimen, apart for the relatively high values of ZW, CW, WB, OHO, and OHB, which are exactly those that separated the Terutau/Langkawi group from the Borneo, Sumatra, and Malaya specimens (see above).

Variation among the small Sundaland islands

An ANOVA of all skulls of specimens from the Lingga, Riau, and Anambas island groups, and from the islands of Tioman and Bunguran (see Fig. 7) suggested that the specimens from Bunguran were distinct, primarily because they are much larger than the other skulls (Table 6). Measurements for BPL, CBL, WB, CW, ML, and MH differed significantly (P <0.01). Compared with those from Borneo, the Bunguran skulls are larger, but significantly so only for CBL (ANOVA, N = 55, P <0.05). The Anambas skulls are smaller than the other Sunda Shelf island specimens, although there is some overlap with the lower end of the Riau, Lingga, Tioman group; in an ANOVA of the two groups only the interbullar distance differed significantly (P <0.01). We further investigated specimens from the small Sundaland islands using bivariate analyses. Three combinations, ML vs. MH, ZW vs. WB, and BPL vs. WB, resulted in a distinct differentiation of the three Bunguran specimens from the rest. One of the three Bunguran specimens was a young adult, and when we restricted the analysis to adult specimens the picture was even clearer (see two examples in Fig. 8 ).

According to Miller (1900) the middle upper premolar (= PM 3) in the only specimen of T. rufulus (from Tioman Island) that he investigated differed from others by its nearly equilateral triangular shape, as opposed to the normally square shape of this tooth. All other teeth were similar to those of T. n. napu . We found similarly shaped premolars in skulls of both the T. javanicus / kanchil and T. napu groups, from Laos, Borneo, Peninsular Malaysia, and Vietnam (note that we only noticed this aberration late in our research and may have overlooked further examples of it), which suggests that this dental character has no taxonomic value.

Table 6. Means and standard deviation (SD) of measurements for mature specimens of T. napu from the small Sundaland islands (mm)

Figures

Figure 8. Bivariate plots for reputed T. napu specimens from the small Sundaland islands.