One reason we're interested in dinosaurs (and why there may yet be a Jurassic Park 4) is that they, like us, ruled the world. Another is that most of these creatures became extinct because they couldn't adapt to a new environment, which in the view of many scientists is where we're headed if we continue to ruin our climate. Now, there's another reason to be curious: We're interested in what we eat, and we worry that obesity is an unstoppable epidemic, but what about dinosaurs' appetites? Did they assist the end of some and the survival of others? " Dinosaur metabolism: Growth factor" appears in the latest issue of Nature (you must be a subscriber to read the article in full), and as Nature editor Henry Gee says of the new research (in a Guardian article not yet available on the Web): "All dinosaurs grew [rapidly] but larger dinosaurs grew absolutely and relatively faster than smaller dinosaurs. The largest piled on 14 kilos [31 pounds] a day." In other words, over a 100-day period some dinosaurs would come to weigh more than the entire Green Bay Packers defensive front line. To grow so big so fast, the appetite of these ravenous beasts required a plentiful food supply; if that supply disappeared with great speed, however, the species died. There was no time to adapt. On the other hand, birdlike dinosaurs may have survived the extinction all around them because they ate so little. As Gee writes: "The researchers think birds began as bonsai dinosaurs: the first birds modified their life history by curtailing the initial dinosaurian growth spurt prematurely. … Adult birds would have had the proportions of chicks: it would be as if humans became sexually mature and stopped growing at the age of five."