Growth of the pouch young, tooth eruption and age determination in the Red Kangaroo, Megaleia rufa

Abstract

Growth of pouch young, molar eruption sequence, and molar progression were studied in a colony of red kangaroos in captivity in order to find criteria by which age could be determined. Methods of measuring young, and methods of examining teeth in the living animal are described. Serial nleasurements of head, ear, arm, hind foot, leg, and tail lengths together with body weights were taken of pouch young of known age and the results are shown as regressions against age. The method was tested by comparing actual ages of a series of pouch young of known age, which were not used when constructing the growth curves, against their ages as calculated from the growth curves. The highest percentage error (about 17 %) occurred in the estimated ages of young less than 20 days old although the actual error was only 3 days. In older young the error in. ages estimated from the growth curves was rarely greater than 5 % and usually much less. There were no differences between growth rates of males and females until they were more than one year old: The ages at which pouch, scrotum, and body hairs appeared, at which eyes and lips opened, and at which other anatomical features appeared are shown. The teeth of semi-adult and adult animals were examined regularly and the molar eruption stage noted. The results were compared with the ages of the animals. Although there was considerable variation in the time of eruption of the individual teeth it is considered that the method offers a practical means of aging kangaroos from the end of pouch life to the time of complete eruption of the last molar at the age of at least 6 years. During the periodical dental examinations the forward movement of the molars relative to the descending process of the zygoma was also noted. Correlation between molar position and age appeared to be less accurate than eruption sequence but after the eruption of the last molar it is probably the only method available for aging except a method based on tooth wear. Unfortunately, the forward movement of the molar row in the jaw slows down with advancing age. In spite of the shortcomings of molar eruption and progression as indices of age the methods based on them are the only obvious practical ones. They are of great value in field ecological studies and it is expected that continuing observations will lead to more precise correlations.