An investigation of criteria for estimating age in the Marsupials Trichosurus vulpecula Kerr and Perameles nasuta Geoffroy.

Specimens of known age, 24 of Trichosurus vulpecula and 7 of Perameles nasuta, were examined so that criteria for estimating age could be established. For T. vulpecula estimates of age based on measurements of the skull and mandible were accurate to within ± 30-40 days up to the age of 1 year when the range of adult size is reached. Adults up to 2.5 years old could be distinguished by the low sagittal crest, which was then 1 mm high or less. Sections of the incisors did not show regular annual rings but the age-classes 0-1 years, 1-3 years, 3-5.5 years, and 5.5 years and older could be recognized from the sections. Lens size was closely correlated with the logarithm of age so that estimates of age became progressively less accurate in older animals. The epiphyses of the limb bones may be used as the basis for three age-classes (0-1 years, 1-c.4 years, and 4 years and older), but it could not be determined whether overlap between the classes was significant. For P. nasuta none of the methods examined gave satisfactory results. Growth of the skull was variable and growth of the lenses became negligible by 1.5 years. Only two age-classes (0-4 months and 4 months and older) could be distinguished from the degree of fusion of the epiphyses of the limb bones.