An account of the dentition of the marsupial family Macropodidae has been provided based on a detailed study of the anatomy and timing of dental development of the grey kangaroo Macropus giganteus Shaw and a comparative anatomical study of the developing dentitions of the red kangaroo Megaleia rufa (Desmarest), the wallaroo Osphranter robustus (Gould), the red-necked wallaby Wallabia rufogrisea (Desmarest), the swamp wallaby Wallabia bicolor (Desmarest), the spectacled bare-wallaby Lagorohestes conspicillatus Gould, the northern nail-tail wallaby Onychogalea unguifer (Gould) and the rufous rat-kangaroo Aepyprymnus rufesoene (Gray).
The macropod dentition has been found to consist basically of seven tooth positions on each side in the upper jaw and five in the lower, described as 3/2 incisor, 1/0 canine, 2/2 premolar and 1/1 molar. Tooth families normally produced at each position number two at each incisor, one at the canine and first premolar, two at the second premolar and five at the molar. Supernumerary successors may be produced at the second premolar and molar positions. The first member of each tooth family at each incisor position is minute and does not erupt, the canine is small and non-functional in most species but functional in some, the first premolar in both jaws and the second member of the family at the first lower incisor position cease development at an early stage and do not calcify. All other teeth present in development erupt and function.
The primary relations of the developing teeth are obscured by their forward movement both before and after eruption (if this occurs). The results of these movements are that the first and second generation incisors come to lie alternately to one another, the second generation tooth at the second premolar position displaces at its eruption the first generation molar, and the successional teeth at the molar position erupt one behind the other so as to form the molar row of the adult.
These findings are discussed briefly in relation to the Zahnreine theory of Edmund (1960) and the field theory of Butler (1939), and some modifications of these theories are suggested.
The macropod dentition has also been considered in relation to the dentitions of other marsupials, mammals and vertebrates in general. It is suggested that the marsupial detition is similar in its essential features to that of the Macropodidae, which may be derived from an ancestral marsupial condition by postulating phylogenetic reduction in the numbers of functional incisors and premolars. Ontogentic evidence of some of these proposed phylogenetic losses has been found. The marsupial dentition, however, appears to represent an adaptation of the two basic features of the vertebrate dentition (which are tooth positions and tooth families at those positions) which differs in significant respects from the adaptation of these features represented by eutherian dentitions. Separate derication of the two groups may thus be indicated.
A system of numbering the macropod dentition to replace the three different systems in current use is also suggested.