Here's Why This Type Of Plant-Eating Dinosaur Was One Of The Most Successful

Most people have heard how the dinosaurs went extinct. Around 66 million years ago, a meteor likely struck the earth, killing off 80% of all species and taking non-avian dinosaurs with it. But what few people realize is that there was another, earlier mass extinction event (there have actually been five mass extinction events, and a possible, current sixth one), one which some dinosaurs actually survived. Called the End-Triassic, this mysterious extinction event killed about 76% of all species around 200 million years ago. And, just as the famous dinosaur-killing asteroid allowed space for mammals to take over the earth, this earlier extinction event was pivotal in freeing up space for dinosaurs called sauropods to rule the Jurassic Period. 

One of the most successful dinosaurs to emerge from the End-Triassic extinction was a clade of plant-eating dinosaurs called the Sauropodomorphs. These giants include some well-known "celebrity" species, such as the giant Brachiosaurus, which gained its fame as the long-necked, plant-munching giant in the original "Jurassic Park" movie. There's also the aptly named Patagotitan, the largest dinosaur to ever walk the earth. Yet, before the End-Triassic extinction, early sauropodomorphs were both relatively small in size and range. It was only once competing dinosaurs went extinct that sauropodomorphs had room to diversify and spread across the planet. 

How exactly the sauropodomorphs evolved to dominate the globe after the Triassic is the subject of a 2021 scientific study from Argentina. Published in Nature, the paper discusses the morphological changes of those early sauropodomorphs as they diversified and adapted to the novel landscapes in the post-mass-extinction landscapes. It seems that the sauropodomorphs' early ancestors already had the blueprints for the clade's future success, specifically by walking on all fours and growing long necks and lightweight bones. With the ideal morphology to support ever-increasing body sizes, sauropods were poised to consume another survivor of the End-Triassic extinction — tall trees.

The team behind the 2021 paper, led by researcher Cecilia Apaldetti of Argentina's San Juan National Institute, compared the fossils of early sauropodomorphs with those that flourished in the post-extinction Jurassic Period, and they discovered a curious pattern. For all the diversity and success of later sauropodomorphs, the clade's fundamental body plans changed relatively little. Instead, the sauropodomorph species that emerged after the extinction event were all based on pre-existing body plans.

If anything, sauropodomorph diversity was restricted even further when life on Earth was soon struck by another, smaller phase of extinction, some 20 million years after the main End-Triassic extinction event. Called the Toarcian Stage, this period led to the extinction of all non-sauropod species within the sauropodomorph clade. With relatively few relatives left, a specific group of sauropods, the gravisaurians, were left to carry on the lineage through the Jurassic.

Though the sauropod feature set was limited, it was ideal for dominating the Jurassic. Their quadrupedal, long-necked bodies allowed them to grow big enough to munch on the tops of trees as other dinosaurs competed on the ground of the post-extinction landscapes. Such a diet was critical to sauropod success. Their extensive stomach systems allowed them to extract nutrients from nutrient-poor shoots, leaves, and pine cones — foods that most other animals couldn't access or digest. Their massive size also provided protection against predators, and they used unique herding techniques to protect their vulnerable young. 

Of course, there is still notable morphological diversity among the over 250 species of sauropods that paleontologists have identified. Species ranged in size from 13 to 120 feet, and each had its own unique dentition. Nonetheless, all sauropods shared one thing in common: They dominated the Jurassic period.