Evolution is not always predictable: Australian kangaroos thrived by evolving thick-enameled teeth to eat grasses, a survival strategy that defied global trends.
Key Findings
A study published in Science and led by Flinders University analyzed fossilized kangaroo teeth from millions of years ago. The research found that kangaroos evolved thickened enamel on their molars as a solution to feeding on grasses.
Unlike hoofed mammals such as deer and horses, which chew side-to-side and have high-crowned teeth, kangaroos slice food vertically and have a conveyor belt of cheek teeth with thick enamel.
"Kangaroos evolved a unique approach: vertical chewing paired with exceptionally thick enamel, rather than the high-crowned teeth seen in northern hemisphere grazers."
Background
Lead author Aidan Couzens stated that feeding on grasses wears down teeth more rapidly than other plants due to dust and tiny silica particles.
The evolutionary history of herbivorous mammals in Australia differs from that on northern continents, where vertical chewing herbivores like kangaroos succeeded while horizontal chewers declined.
Implications
The study suggests that evolution is not always predictable.
Competing marsupial herbivores declined before grasslands spread, allowing kangaroos to take advantage of the ecological opening. This timing, rather than direct competition, may have been the key driver of their eventual success.