Over-eruption in marsupial carnivore teeth: compensation for a constraint

Abstract Pronounced over-eruption of the canine teeth, much greater than in eco-morphologically equivalent placental carnivores, occurs with age and growth in Australian marsupial carnivores. Suppression of functional tooth replacement is a characteristic of marsupials and is frequent among diverse placentals, where the primitive therian pattern is two generations of incisor, canine and premolar teeth. Rapid determinate growth is one among multiple hypotheses proposed to explain the loss of tooth replacement in mammals. In this line of reasoning, the animal reaches a sufficient body or jaw size to accommodate adult-sized teeth by the time it requires functional dentition. Marsupial carnivores have a full set of adult anterior teeth at weaning, which erupt into a juvenile jaw that is 25 to 30 % adult size, compared with well grown in placental carnivores. Indeterminate over-eruption of the canine teeth in marsupial carnivores results in increasing canine height and diameter with increasing body size with age, suggesting this is a compensatory mechanism for the constraint of a single generation of anterior teeth. Patterns of over-eruption in different tooth types of marsupial carnivores are consistent with two non-exclusive mechanisms that operate in other mammals, a response to tooth wear and lack of an occlusal partner.