The Rise and Reign of Dinosaurs
The Latecomers Emerge
Dinosaurs belonged to the larger group of archosaurs which emerged after the devastating end-Permian mass extinction around 252 million years ago. This catastrophic event wiped out approximately 90% of life on Earth at the time. While mammals, turtles, lizards, amphibians and fish also survived, archosaurs had certain advantages that helped them thrive in this new post-apocalyptic world. Upright posture allowed for faster and more efficient movement compared to sprawling reptiles. An advanced respiratory system enabled better breathing and temperature regulation. The first dinosaurs appeared in the late Triassic period around 230 million years ago in what is now Argentina. These were small and nimble creatures that likely ate insects and plants.
Coexistence with Other Archosaurs
During the late Triassic, dinosaurs coexisted with other archosaurs such as the large carnivorous rauisuchians and armored herbivores called aetosaurs. However, around 201 million years ago climate change and volcanic eruptions drove most of these competitors to extinction. This created new ecological opportunities that dinosaurs were poised to take advantage of. The Jurassic period from 201-145 million years ago was the golden age for dinosaurs. They diversified into many body forms from tiny feathered theropods to gargantuan sauropods. As the supercontinent Pangaea broke apart, dinosaurs spread across the globe colonizing separate emerging continents. They also faced novel challenges from marine reptiles, flying reptiles, and early mammals.
Dominating the Land
During the Cretaceous period spanning 145-66 million years ago, dinosaurs continued adapting to changing environments and climate. Some evolved horns, crests, spikes and armor for combat or display. Birds emerged from feathered theropod dinosaurs, representing living dinosaurs today according to many paleontologists. Dinosaurs ruled terrestrial ecosystems with no competitors able to dethrone their dominance. This reign came to an abrupt end 66 million years ago with an asteroid impact that precipitated the Cretaceous-Paleogene mass extinction. Billowing debris blocked sunlight for months creating global winter, while firestorms and acid rain decimated the fragile ecosystems dependent on photosynthesis.
Feathered Flyers Emerge
Feathered dinosaurs were among the earliest birds to emerge in the Jurassic period around 160 million years ago. Archaeopteryx possessed characteristics of both dinosaurs and birds with feathered wings, claws on its wings and a long bony tail. While not capable of true flapping flight, it could likely glide between trees. In fact, many small coelurosaurian theropods from this time displayed primitive feathers that could have aided gliding or provided insulation. By the Cretaceous period, birds diversified into true flapping flyers filling aerial niches vacated by pterosaurs in decline. Toothless beaks evolved for snatching prey while sophisticated wishbones powered strong wings. Around 50 million years ago, primitive carnivorous birds the size of crows prowled the northern continents of Gondwana preying on lizards and small mammals.
Marine Giants Emerge
Around 150 million years ago during the Jurassic, islands with flourishing vegetation first appeared off the coast of fragmenting Pangaea attracting titans of the seas. Plesiosaurs developed long flexible necks and paddle-like flippers to opportunistically feed on squid, fish and ammonites. Elasmosaurus grew over 10 meters in length making it the longest known marine reptile. Mosasaurs arose on land but some lineages like Mosasaurus eventually lost their legs and invaded the oceans. By the late Cretaceous they hunted prey as large as whales making them the dominant marine carnivores. Meanwhile, gigantic plankton-feeding pachypleurosaurs over 30 feet long skimmed the water like basking sharks filtering food through gill rakers in their throats. Dominating both land and sea, dinosaurs and their contemporaries reigned supreme across ecosystems for over 160 million years.
Rise of the Titans
During the late Jurassic and Cretaceous periods, sauropods evolved to epic sizes with some reaching lengths over 30 meters. Giraffe-like necks towered high while pillar-like legs supported over 100 ton bodies. As the largest animals to ever walk the Earth, these colossal herbivores required immense quantities of ferns, conifers and cycads just to sustain themselves. Sauropods likely benefitted the wide dispersion of seed plants during this time. With small heads but expansive chest-like regions and multiple stomach chambers, they could continuously graze and digest vegetation. It’s thought their efficient metabolisms and gigantothermy allowed homeothermy without expending too much energy. The presence of these walking mountains must have transformed the ecology and appearance of habitats worldwide wherever they existed. Although outcompeted by hadrosaurs and ceratopsians later in the Cretaceous, sauropods showcased the incredible heights dinosaurs were able to evolve to during their reign over terrestrial tetrapods.
Monarchs of the North
Around 85 million years ago, the plates forming Asia began their separation from North America allowing for faunal exchange and new evolutionary radiations on the northern continents. Hadrosaurs like Edmontosaurus and Saurolophus diversified to over 7 meters in length becoming the dominant herbivores of Laramidia, which comprised western North America and northeastern Asia separated by the Western Interior Seaway. With batteries of constantly growing teeth allowing efficient grinding of vegetation, these duck-billed dinosaurs formed vast migratory herds by the Late Cretaceous. Meanwhile ceratopsians like Triceratops, Pentaceratops and Torosaurus evolved horns and frills likely used for territorial displays and combat. Many species exceeded 9 meters long and tipped scales over 5 tonnes as the largest terrestrial herbivores in their ecosystems. Presiding over these northern realms as apex predators were tyrannosaurs. Teratophoneus, Daspletosaurus and the king of all—Tyrannosaurus itself—which grew over 12 meters long and wielded bone-shattering bites with serrated teeth as their uncontested superpredators. By 66 million years ago, these dynamic faunal assemblages dominated Larimidia until being shattered by a fate beyond their control.
The End of an Era
About 66 million years ago a massive asteroid struck what is now the Yucatán Peninsula marking an abrupt end to the age of non-avian dinosaurs. Impact winter and surging global wildfires precipitated a calamitous mass extinction that wiped out over 75% of all plant and animal species within a matter of months, including all non-avian dinosaurs. While some lineages like birds, crocodilians, and marine reptiles managed to cling on, the Cretaceous saw the demise of dinosaurs which had been terrestrial tetrapods’ dominant clade for over 160 million years. The end paved the way for new mammalian lineages to diversify and fill vacant ecological niches vacated by dinosaurs and other victims. Although none lived to see the dawn of the Cenozoic era, dinosaurs left an indelible mark on life and profoundly shaped ecosystems worldwide during their unparalleled reign stretching hundreds of millions of years from the late Triassic to the fateful Cretaceous period. Today their extraordinary fossil remains continue to inspire awe and illuminate evolutionary history on a truly monumental scale.
