Teeth tell tales: new study reveals how kangaroo incisors indicate age and sex
Credit: William Parker
A study led by Monash University biologists and published in Archives of Oral Biology has unveiled a novel method for determining the age and sex of Australian marsupials using their teeth. The research provides major insights for vets, ecologists, and conservationists.
The study found that the front teeth of kangaroos, known as incisors, record their age in various ways. Remarkably, these teeth can even reveal if a kangaroo is male or female.
Understanding the age of wild animals is crucial for wildlife welfare and assessing the health of populations.
Without the ability to count birthdays in the wild, scientists often turn to the teeth of animals for clues.
Most of Australia’s marsupials belong to the order Diprotodontia, characterised by large, straight incisor teeth in their lower jaws. This group includes kangaroos, wallabies, koalas, wombats, and possums.
The researchers measured the growth of these incisor teeth in Eastern Grey Kangaroos (Macropus giganteus), Western Grey Kangaroos (Macropus fuliginosus), and the dentally reduced Honey Possum (Tarsipes rostratus).
“We found that these incisors grow continuously throughout the animal's life, allowing us to determine age based on their length,” said lead study author William Parker, a PhD candidate at the Monash University School of Biological Sciences,
“This study demonstrates that the incisors of Diprotodontian marsupials are effective tools for determining age and sex,” he said.
“These findings have far-reaching implications for population ecology, conservation efforts, and the study of marsupial evolution.
“By understanding the growth and wear patterns of these teeth, scientists can gain a deeper insight into the lives of both living and extinct marsupials.”
Similar to how trees have growth rings, teeth have growth lines. These lines form as enamel, dentine, and cementum—the hard tissues making up a tooth—are added over time. The study revealed that yearly growth lines are present in two regions of kangaroo incisor teeth, providing a reliable record of age.
Another fascinating method of aging kangaroos involves their molar teeth.
Kangaroos have a unique adaptation where their molars move forward in the jaw over time, akin to a conveyor belt. Old, worn teeth are pushed forward and fall out, making way for new, unworn teeth. This molar progression corresponds accurately with age, similar to the process observed in elephants.
The study also investigated differences between male and female kangaroo incisors.
“We found that male kangaroo incisors generally grow faster and wear down more quickly than those of females,” said co-study author Professor Alistair Evans, also from the School of Biological Sciences.
“This information is vital for understanding animal ecology, as it indicates different foraging and feeding behaviours between the sexes,” he said.
The methods developed in this study can also shed light on the lives of extinct kangaroo species.
Thousands of years ago, Australia was home to a diverse range of giant kangaroos.
“Our new techniques can help determine the age and sex of these extinct animals from fossilised teeth, providing valuable insights into their ecology and evolution,” Professor Evans said.
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