Growth of Grey Kangaroos and the Reliablility of Age Determination from Body Measurements III. Interspecific Comparisions between Eastern and Western Grey Kangaroos, Macropus giganteus and M. fuliginosus

Abstract

Seven body measurements were taken at regular intervals throughout life from both male and female eastern and western grey kangaroos. Evaluation of the reliability of criteria for determination of age and some aspects of the growth models for the two species were presented in earlier papers in this series. In this paper the common patterns and relationships between species in the growth characteristics of their body parameters are described and analysed. Comparison is made between species and sexes of rates of growth and size attained both within the pouch and following vacation of the pouch. Head, arm, leg and foot length were important discriminators, particularly when contrasted in various ways to summarize different body proportions. The insular form M.f. fuliginosus readily separated from the mainland forms, and M.f. ocydromus showed some differences which were related to its longer pouch life. Hybrid animals showed growth patterns intermediate to those of their parents. Sexual dimorphism in patterns ofgrowth was not detected during pouch life but was exhibited by all species after the young vacated the pouch and grew towards their full adult size.

Pleistocene Grey Kangaroos from the Fossil Chamber of Victoria Fossil Cave, Naracoorte, South Australia

“…Table 3 shows means, standard deviations (sd), and overall size ranges of the "adult" cranial and mandibular material. "Adult" was classified as specimens with M2 fully erupted and correlates to individuals of greater than four years old (Poole et al 1984). As the amount of cranial material available from the VFC-FC deposit was minimal (<12 specimens per character), statistical tests on differences between means were not performed.…”

“…Thus a representative age, based on some dental characteristics must be selected. For example, Poole et al (1984) defined age categories based on the eruption status of the molar teeth. (2) Molar progression: Grey kangaroo dentition is never stable.…”

A natural grey kangaroo hybrid?

“…The differences are reinforced by characteristics of the ears, which are usually concave on the distal half of the outer edge in western grey kangaroos. The ears of western grey kangaroos are also relatively longer (Poole et al 1984), more sparsely furred (Wallis, 1989), more darkly pigmented on the back, and are often carried lower by comparison with eastern grey kangaroos ( Fig. 1).…”

“…1). Hybrids produced in captivity are intermediate in pelage characteristics (Kirsch and Poole 1972) and in body proportions (Poole et al 1984).…”

Estimating the age of kangaroos using eye lens weight

“…Current methods for age estimation in kangaroos are based either on dentition of an intact skull (Kirkpatrick 1964(Kirkpatrick , 1965(Kirkpatrick , 1970, on morphometric characteristics (Wood et al 1981;Poole et al 1982aPoole et al , 1982bPoole et al , 1984Edwards et al 1994) or on protein content of the eye lens (Augusteyn et al 2003). These alternatives have advantages and disadvantages.…”