Age determination in lorises and pottos
Age grades, based on Schultz (1959) and other sources:
Fetus: all stages of prenatal life between the embryonic and the newborn.
Infant: from shortly after birth to, but not including, the appearance of the first permanent teeth
Juvenile I: stage during which the first few permanent teeth erupt.
Juvenile II: all later phases of dental eruption, following as a rule after a considerable period of rest, until the last teeth have appeared, though without full occlusion
"Subadult": animal not yet fully grown, but clearly too old to be classified as dependent young. Subadult specimens may already be sexually mature (Ansell 1965).
"Adult": from the completion of dentition to the stage in which most teeeth have become strongly worn and certain cranial sutures are closed (Schultz 1959).
Since the word "adult" in literature is not used in an unmistakeable way, Ansell (1965) proposes to distinguish between the following adult stages not necessarily coinciding:
a) with complete permanent dentition (a frequent taxonomic criterion for adulthood)
b) physically mature (having reached maximum body development)
c) sexually mature
Senile: according to Schultz very old specimens with extreme wear of the teeth and signs of bony atrophy. In captive Loris, in animals of 11 to more than 15 years who partly showed other signs of ageing towards the end of their life, little toothwear was found. Instead, a variety of other changes independently occurred, including grey to white facial hair (circumocular patches), patchy pigmentation of the skin, decreased vision, cataract, loss of weight, thinning of the fur, loss of some teeth and tartar, but onset of these changes varied individually.
Infant development in L. t. nordicus
Behavioural and weight development in captive-bred mother-reared single offspring and twins of L. t. nordicus from Polonnaruwa, Sri Lanka. Data: B. Meier
Age-related changes in captive L. t. nordicus from
Neonate colour: light grey to reddish-grey with few darker stiff hairs, with a reddish dorsal stripe and reddish circumocular patches. Limbs almost naked, unpigmented, ears with slightly pigmented rims.
Juveniles: light yellowish without white frosting (white hair tips), with reddish circumocular patches; ears yellowish with slightly pigmented, darker rims.
Change to grey adult colour: gradual; usually the development of some blackish hair in the upper part of circumocular patches is noticed first (starting at the age of about 6 months or later). The yellowish juvenile coat gradually changes into adult grey colour with more or less frosting, with some chestnut hair on the forehead in some subadult specimens. The ear pigmentation vanishes. Adult colour: usually pure grey, seldom yellowish-grey. Specimens in some recorded cases resembled their parents at the age of 16 to 21 month.
The skin of younger adults is unpigmented and yellowish or pink. With increasing age, an irregular, grey pigmentation may develop. It is particularly visible on muzzle, ears (particularly ear rims) and dorsum of hands and feet. The age of onset of this pigmentation varies individually.
In ageing animals, the fur of the face, and to a lesser degree of the trunk, may become increasingly grey to almost white. One specimen with initially almost black circumocular hair was already rather grey at the age of five years and at the age of 9 years showed a very light grey to almost white face, a feature apparently inherited from the wildcaught father who also showed some white facial hairs at a rather early age and was almost white when he died after 13 years in captivity. Another wildcaught female after 13 years in captivity still showed black circumocular patches without white hair.
Some information for slow lorises and pottos: see table
juvenile colour descriptions in the population database
References, further age determination
Ansell, W. F. H., 1965: Standardisation of field data on mammals. Zoologica Africana 1 (1): 97-113.
Berry, R. J., 1970: Covert and overt variation, as exemplified by British mouse populations. Symp. zool. Soc. Lond. 26: 3-26.
Berry, R. J.; Truslove, G. M., 1968: Age and lens weight in the house mouse. J. Zool. Lond. 155: 247-252.
Deol, M. S.; Grüneberg, H.; Searle, A. G.; Truslove, G. M., 1951: Genetical differentiation involving morphological characters in an inbred strain of mice. I. A British branch of the C57BL strain. J. Morph. 100: 345-376.
Jungers, W. L., 1985: Body size and scaling of limb proportions in primates. Pp. 345-381 in: W. L. Jungers (ed.): Size and scaling in primate biology. Plenum Press, New York.
Martin, R., 1914: Lehrbuch der Anthropologie. Gustav Fischer Verlag, Jena.
Molez-Verričre, N.; Vincent, F., 1997: Dental age determination in young bushbabies. Folia Primatologica 68: 106-109
Schultz, A. H., 1959: Post-embryonic age changes. Pp. 887-964 in: Primatologia I, Hofer, H.; Schultz, A. H.; Starck, D. (eds.), Karger, Basel.
Silberberg, M.; Silberberg, R., 1941: Age changes of bones and joints in various strains of mice. Am. J. Anat. 68: 69-95.
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