28 février 2010
Origines surprenantes des grands oiseaux terrestres
On a longtemps pensé que tous les Struthioniformes (des oiseaux incapables de voler, tels que l'autruche, l'émeu, le moa, le casoar ou le kiwi) devaient avoir un ancêtre commun. Une nouvelle étude semble démontrer que non, que chacune de ces espèces aurait évolué séparément. Encore plus intéressant, le plus proche cousin du moa ne serait pas l'émeu australien, mais bien un petit oiseau qui vit toujours en Amérique du sud!
Extrait de l'article:
It's been long thought that the ancestors of ostriches, emus, and other flightless birds that once flew were flightless too. But a new study says that they only began exploring the ground in earnest after dinosaurs were wiped out about 65 million years ago. The sudden disappearance of dinosaurs opened up new, predator-free niches, where food was plentiful and flight wasn't needed for quick escapes, said study leader Matthew Phillips of the Australian National University in Canberra. The birds then got so plump that they became too heavy to fly, whether they wanted to or not, the study suggests.
That flightless birds evolved species by species, as the new research indicates, challenges a previous theory that flightless birds evolved from a common flightless ancestor, the study says. (...) The new findings also appear to solve the ancient mystery of how flightless birds ended up on various continents. "There used to be odd ideas about how [supposedly flightless] birds got over marine barriers," Phillips said. "But the fact that these birds all had independent ancestors that could fly explains how they got to different land masses—they flew."