How dinosaurs got big (and small)

Extinct theropod dinosaurs, which include iconic species such as Tyrannosaurus rex, used more than one evolutionary trick to become big: some had explosive growth spurts, whereas others grew slowly over time. Palæontologists had always assumed that dinosaurs developed like modern birds and mammals, in which larger species grow faster during their most rapid growth period. Now, researchers who analysed growth rings in the shin bones of 42 dinosaur species have discovered that this is true for only 31% of theropods — 28% showed prolonged growth similar to that of modern crocodiles. Of the species that became smaller than their ancestors, 21% did so by shortening their growth spurts and 19% by slowing their growth.