National Geographic : 2015 Aug
Ancient Worlds EXPLORE Dinosaurs not drawn to scale GRAPHIC: MATTHEW TWOMBLY, NGM STAFF. SOURCE: ROGER BENSON TO LIVING BIRDS TRIASSIC 250–200 million years ago JURASSIC 200–145 mya CRETACEOUS 145–66 mya Argentinosaurus 100 tons Apatosaurus 44 tons Apatosaurus 44 tons Stegosaurus 8 tons Fruitadens 1.6 lbs Triceratops 15 tons Shantungosaurus 19 tons Iguanodon 9 tons Iguanodon 9 tons Tyrannosaurus 8 tons Tyrannosaurus 8 tons Spinosaurus 7 tons Spinosaurus 7 tons Velociraptor 33 lbs Velociraptor 33 lbs Archaeopteryx 2.2 lbs Archaeopteryx 2.2 lbs Qiliania 0.03 lbs Qiliania 0.03 lbs Common dinosaur ancestor 25–75 lbs AvialaeManiraptoraTheropodaSauropodomorphaOrnithischia Not all dinosaurs went extinct. Their descendants live on in the Avialae group, aka birds. Hoping to learn how this group thrived when others didn’t, scientists measured hundreds of dinosaur femur bones to determine each creature’s mass. The survivors’ continual evolution and ecologi- cal diversity helped them fit into shifting niches, the researchers found. For avians, survival hinged on shrinking in size. —L indsay N. Smith Living Small OPPORTUNITIES FOR CHANGE Small mass often co- incides with frequent reproduction, allowing for more variation. RAPID DEVELOPMENT Maniraptoran thero- pods evolved quickly and often. But apart from Avialans, no species from the lineage survive today. LAYING THE FOUNDATION Theropods, primarily bipedal carnivores, shared traits with modern birds, includ- ing hollow bones and sometimes feathers. BIGGEST DINOSAURS The Argentinosaurus was more than six mil- lion times the size of the smallest Mesozoic bird, Qiliania graffini. STALLED EVOLUTION Lineages whose size evolved rapidly during early development but then halted were at a disadvantage when change was crucial for survival.