Preliminary identification key for slender loris subspecies


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Preliminary identification key for slender loris subspecies
Sorry - because of lack of time and ongoing taxonomic research here still the old names / sysnonyms are used, the grey dry forest forms are now species Loris lydekkerianus. Update soon

The classification of Loris subspecies by Osman Hill (1953) considers geographic origin, minor variation in pelage colour, size and weight and some additional characters. Some Loris subspecies may turn out to be identical, and undescribed species may exist within the genus (Groves 1971, Groves 1998, Jenkins 1987). In Goonan et al. (1995) and Groves (1998), L. t. nordicus is considered indistinguishable from L. t. grandis and therefore probably a synonym of the latter (see below: 6b); photos of both forms, however, show different-looking animals, and subspecies descriptions also mention differences. Karyotype polymorphism has been discovered in the genus (Goonan et al., 1995), but the examined specimens were captive animals of unknown geographic origin, and it seems doubtful whether they had been correctly identified. Taxonomic identification of Loris specimens of unknown geographic origin is generally difficult because of the following problems:

a) Descriptions of presently distinguished forms are based on small samples, and Osman Hill focused on features distinguishing L. t. tardigradus and L. t. grandis whereas differences to other forms seem to have been somewhat neglected.

c) At least some described forms seem to intergrade (see below, 6 a). Among small reddish and brown lorises imported from Sri Lanka, for instance, usually identified as L. t. tardigradus, different-looking forms can be distinguished. They might be representatives of a cline variation between L. t. tardigradus and L. t. grandis (see Osman Hill 1942) or represent undescribed distinct forms.

d) According to Mewa Singh (pers. comm.), lorises imported from Sri Lanka are not necessarily representatives of Sri Lankan forms because smuggling of lorises between India and Sri Lanka may occur.

Because of the limited reliability of distinguishing features, the identification key below does not yet allow a clear identification; consideration of as many features as possible including geographic origin, if known, remain necessary. A verification of taxonomy, considering ecological differences and reproductive separation, and discovery of reliable phenotypic differences allowing to identify live animals would be desirable for conservation.

1) Hair length up to 3 cm (extreme highland form), ears completely hidden by fur, limbs thickly furred, superficially nycticebus-like; dorsal colour: earthy-brown with no reddish tinge; origin: montane rain and mist forests of the central highland of Sri Lanka (Horton Plains):
L. t. nycticeboides Osman Hill, 1942.
(Existence of similar, thickly furred forms in higher regions of India?)

2) Relatively small animals (head-body-length up to 22 cm, weight about 85 - 135 g, foot length 35-45 cm), fur soft, velvety with little true hair, brown, reddish or brownish-grey: rainforest forms, L. t. tardigradus or L. t. malabaricus; see figure 1 3

Relatively small animal; fur yellowish or reddish-yellowish, reddish circumocular patches. Ears in infants from Polonnaruwa yellowish with a slightly pigmented rim, in other regions pigmantation possibly more variable; see below, under 5:
Possibly juvenile L. t. nordicus. (See under 5: large grey dry zone forms).
(Juveniles of L. t. lydekkerianus similar? One juvenile / subadult L. t. lydekkerianus was described as greyish-buff with chestnut circumocular patches (Osman Hill 1933).

Recorded head-body-length 19.8-25.6 cm, foot length 38-47 mm. Distal parts of limbs well covered with fur. Dorsally dark grey, blackish or brownish-grey, in males sometimes slightly rusty on lumbar region . Throat hair pure white throughout, ventral colour pure white or only slightly buff with dark hair bases, white zone surrounding the dark circumocular patches, preauricular hair between this zone and the ears clearly darker. (In some L. t. nordicus from Polonnaruwa the circumocular patches are also surrounded by whitish hair, but then preauricular hair closer to the ears is whitish or very light grey with no marked contrast to that around the circumocular patches). Fur according to Osman Hill more coarse with a higher amount of true hair than in the more soft, velvety fur of the other forms which mainly consists of woolly hair. Photos show animals with a peculiar facial appearance (heart-shaped face with the appearance of a long muzzle): see figure 2. (A facial appearance as in L. t. grandis is also found in some small reddish specimens imported from Sri Lanka; see figure 1 f - h; see below, under 6 a, possible intermediate form).

(Features above mainly based on Osman Hill´s data. According to Goonan et al., 1995 and Groves 1998 examined skins were said to be indistinguishable from L. t. nordicus skins)

Recorded head-body-length 20.5-26 cm, foot length 45-56 mm, weight usually more than 220 g in adults; fur soft, grey, yellowish-grey, grey-brown, buff or dirty deep fawn (in subadults occasionally with a slightly reddish forehead):
large grey dry zone subspecies, L. t. nordicus or L. t. lydekkerianus; see under 5, 6b.

3) Origin: India; head-body-legth 18 - 22 cm (weight data insufficient, 170 g mentioned), foot length 44-45 mm, throat hair buff throughout (hair bases coloured like tips), ventral colour buff or dirty white:
L. t. malabaricus Wroughton, 1917, Malabar slender loris.
(Throat hair colour: difference to L. t. tardigradus? But see under 7 a). The distribution area of this form includes lowland and highland regions; density and length of fur might differ.

4) Origin: Sri Lanka; head-body-length 18.2-20.6 mm, reported weight about 85 - 142 g, foot length 35-44 mm; throat hair buff with dark grey hair bases (throat hair colour: difference to L. t. malabaricus? Some captive small reddish or brown animals belonging to stock from Sri Lanka show an entirely white throat, see under 6a). Ventral colour buff or yellowish, preauricular hair grey, never white, velvety fur with a minimum of true hair, distal parts of limbs sparsely haired or hairless:
L. t. tardigradus Linnaeus, 1758, Slender loris (see figure 1 a - h).

Origin: Sri Lanka. Head-body-length in wildcaught animals 20.5 - 23.8 cm, in large captive-bred animals up to 26 cm. Weight, 198 - 360 g; in wildcaught animals from Polonnaruwa 228 - 287 g (566-679.2 g for Wilachchiya animals probably erroneous) ; foot length 42-55 mm. Ear pigmentation possibly variable, yellow ears; in a population of L. t. nordicus from Polonnaruwa with unpigmented yellow ears, juveniles with pigmented brown ear rims; according to Osman Hill black ears (erroneous?). Bases of ventral hair usually with a grey base (in some specimens from Polonnaruwa, hair at least in the median part of ventral side white throughout or with very light grey, almost white bases), lowland form with thin fur on dostal parts of limbs. In captivity non-seasonal breeder.:
L. t. nordicus Hill, 1933, Northern Ceylonese slender loris
(but see below, 6 b: no difference between L. t. nordicus and L. t. grandis?).

Origin: India. Head-body-length 22.3 - 26.3 cm,weight 226.8 - 346.6 g, foot length 45 - 57.5 mm. Ears dark or with a dark rim (at least no information about populations with unpigmented ears has been found); bases of ventral hair usually without, seldom with a tiny grey base. Distribution area including lowland and highland regions, local differences in length and density of fur seem possible. Evidence for seasonal breeding both in captivity and in the wild: L. t. lydekkerianus Cabrera, 1908, Mysore slender loris.

6 a) Intermediate forms between L. t. grandis and the lowland forms of Sri Lanka are reported from the wild, intermediate tardigradus / grandis forms for instance occurring in the hills near Kandy (Phillips, 1935). Wildcaught specimens of unknown origin, imported from Sri Lanka, resembled L. t. tardigradus with regard to small size and the lack of a white zone around the circumocular patches, but showed an entirely white throat and the facial appearance as in L. t. grandis (with a "long muzzle", see figure 1 f - h).

6 b) Difference between L. t. grandis and and the adjacent lowland form L. t. nordicus: Osman Hill describes differences whereas, according to Goonan et al., 1995, no differences between preserved skins and skulls of L. t. grandis and L. t. nordicus in the Natural History Museum, London, were found. A white throat and white zone around the dark circumocular patches are not only found in L. t. grandis, but also in some L. t. nordicus from Polonnaruwa; in the latter, however, preauricular hair behind such a white rim is not clearly darker, but also whitish or very light grey. In two live grey Sri Lankan lorises kept in Adelaide (exact origin of both unknown), phenotypic and karyological differences were found (Goonan et al., 1995). The conclusion in Goonan et al. from these findings was that L. t. nordicus and L. t. grandis probably belong to one subspecies of grey lorises, but that some local differences may still be present. If both forms were identical, L. t. nordicus would be a synonym for the older name L. t. grandis.