The study shows that Australia was unusual in that marsupial herbivores like kangaroos with teeth and jaws that slice food using a vertical action expanded their diversity more than did herbivores which chew from side-to-side (“transverse”) like the wombats, koalas and their ancestors. This was the opposite of trends on other continents where side-ways chewing herbivores (e.g., deer, antelope) win-out over vertical slicers (tapirs, primates, primitive herbivores).