When dinosaurs became extinct, some birds got fat and lost their ability to fly, concludes a new study that helps to explain the existence of modern hefty birds, like ostriches, rheas, kiwis, emus, and cassowaries.

The very basic process is that when an animal, or multiple species, die out, others can come in to fill the previously occupied ecological niche. (It makes me wonder what animal(s) would fill the ecosystem void left by humans, should we become extinct.)

Matthew Phillips, an evolutionary biologist at the Australian National University, and his colleagues analyzed DNA for flightless birds, along with other data, to determine how the birds evolved. The study, published in the latest issue of the journal Systematic Biology, found that the ancestors of these birds, palaeognaths, could all fly. These ancient birds then all independently lost this ability around 65 million years ago, just as dinosaurs were going extinct. A coincidence? No.