THE EXPLAINER
WHY WERE THE DINOSAURS SO SUCCESSFUL?
HOW SUCCESSFUL WERE THE DINOSAURS?
By every objective measure, dinosaurs were hugely successful. During much of the Mesozoic Era (252-66 million years ago), they dominated ecosystems on land, living in every conceivable environment from the poles to the equator, and from the seashore to the river valleys to the deep mountains. They diversified into thousands of species, ranging in size from feisty carnivores like Microraptor (about the size of a crow) to behemoth plant-eaters like Brontosaurus, with the heft of a jet aeroplane. Some were specialised runners, others diggers, and some even glided and flew. Some species were covered in armour and spikes, others had endless varieties of horns and crests for display, many lived in groups and had big brains and keen senses, and it seems like many dinosaurs – if not all of them – were covered in some type of feather. Indeed, today’s birds evolved from dinosaurs, meaning that 10,000-plus species live on, continuing dinosaur success to the present day.
WHAT WERE THE FIRST DINOS LIKE?
Dinosaurs evolved in the Triassic, which began around 252 million years ago, after the most severe mass extinction in Earth’s history. Massive volcanic eruptions in Siberia led to runaway global warming, which killed up to 95 per cent of all species. Among the survivors were small, cat-sized reptiles that could run fast. These dinosauromorphs were the ancestors of dinosaurs. Around 230 million years ago, they gave rise to true dinosaurs, which are distinguished by their upright legs that fit into a window-like opening in the pelvis, which is attached to the backbone by extra vertebrae. These features allowed the first dinosaurs – like Eoraptor and Herrerasaurus – to run faster, cover larger distances, and expend less energy than most other animals of the time. These first dinosaurs diversified and split into the three fundamental divisions of the dinosaur family tree: the carnivorous theropods, long-necked sauropods, and beaked, plant-munching ornithischians.
HOW DID SOME DINOSAURS GET SO BIG?
We don’t yet know why the dinosaurs survived the end-Triassic extinction while crocs were almost wiped out, reduced to a few lineages that produced today’s alligators and crocodiles. What we do know is that in the ensuing Jurassic Period the dinosaurs spread around the world and got much larger. The sauropod dinosaurs like Brontosaurus, Diplodocus and Brachiosaurus were the heavyweights of the time. These were the largest animals to ever live on land, some of them exceeding 80 tonnes in mass – more than the take-off weight of a Boeing 737. Why were they able to get so big? Their ultra-efficient lungs were probably key. These bird-style lungs were connected to air sacs, which stored extra oxygen-rich air, allowing these dinosaurs to take in more oxygen per breath than a mammal like us.
HOW DID THE EARLIEST DINOSAURS BEAT THEIR RIVALS?
The first dinosaurs didn’t take over the world right away. Rather, it took them more than 30 million years to assert their dominance. They were evolving in a world very different from today, as all land was joined into the supercontinent Pangea, which stretched from pole to pole. Sharing this landmass were early crocodiles and their relatives, which were the main competitors of the early dinosaurs. For most of the Triassic, the crocs were pulling ahead of the dinosaurs: there were more species of them, they had a greater richness of body sizes, diets and behaviours, and they lived across a broader range of Pangea. But just when it looked like the crocs were poised to defeat the dinosaurs, Pangea began to split, around 200 million years ago. Volcanoes erupted with gusto, spewing out greenhouse gases, causing global warming and another mass extinction. The crocs were decimated, but the dinosaurs survived nearly unscathed.
HOW DID THEY BECOME AIRBORNE?
Not all dinosaurs were enormous. One group, the paravian theropods, went in the opposite direction. Like most dinosaurs, the first paravians sported simple, hair-like feathers, which probably helped to keep them warm. As the paravians got smaller over time, the feathers on their bodies became larger and more packed together. Then they began to line up their feathers on their arms, to form wings. These first wings were too small to keep these dinosaurs aloft; instead, they were probably used for display. At some point, though, a threshold was crossed. The wings became big enough that, when flapped, they could provide a bit of lift and thrust, and keep these paravians airborne. Flight had evolved! From these flapping ancestors arose today’s birds. In other words, birds are dinosaurs! So while Triceratops, T. rex and the other famous dinosaurs went extinct 66 million years ago, some dinosaurs live on.