Trying to bring down a fully grown Brachiosaurus would have been a reckless gamble for any predator. Weighing as much as 60 tonnes and towering over most other dinosaurs, the long-necked giant was among the largest land animals ever to walk the Earth.
But new research suggests that meat-eating dinosaurs 150 million years ago rarely took such risks. Instead, they went after much smaller — and far more vulnerable — targets.
Scientists have found that baby and young juvenile sauropods were a staple food source for top predators during the Jurassic Period. By reconstructing the ancient food web of a fossil-rich ecosystem at the Dry Mesa Dinosaur Quarry in southwestern Colorado, researchers mapped out in detail who ate whom in a landscape teeming with life.
The Dry Mesa ecosystem supported at least six species of sauropods — including Brachiosaurus, Diplodocus, Apatosaurus and Supersaurus — alongside five types of large meat-eating dinosaurs. The area was also home to other plant-eating dinosaurs, flying reptiles known as pterosaurs, early mammals, crocodile-like reptiles, fish, insects and smaller reptiles, forming one of the most complex prehistoric communities ever studied.
The analysis showed that young sauropods, not their colossal parents, were the most common prey for carnivorous dinosaurs. "These sauropods would have been high in abundance compared to larger adults and were relatively defenceless and slow-moving," said lead author Cassius Morrison, a palaeontologist at University College London. "That made them easy to catch and a perfect snack."
Although adult sauropods could stretch up to 30 metres long, their lives began humbly. Hatchlings emerged from eggs barely a foot wide and took many years to grow to full size. Evidence suggests they received little to no parental care, leaving them exposed during their most vulnerable years.
"Adult sauropods relied on their enormous size, long tails and herd behaviour for protection," said ecologist Steven Allain of Anglia Ruskin University, a co-author of the study. "Unfortunately, juveniles hadn't yet reached that 'too big to mess with' stage. They lacked armour, spikes or heavy plates, making them far easier to subdue than dinosaurs like Stegosaurus, whose spiked tail could seriously injure or kill a predator."
The hunters of the Dry Mesa ecosystem were formidable in their own right. Torvosaurus, stretching up to nine metres long, and Allosaurus, measuring about eight metres, sat at the top of the food chain. They were joined by Ceratosaurus, Marshosaurus and the smaller Stokesosaurus. Even so, attacking a healthy adult sauropod would have been extremely dangerous.
"Hunting a full-grown Brachiosaurus would have been a high-risk task for even the largest theropod," Allain said. "One well-placed tail swing or a simple sideways step could seriously injure or kill a predator." As a result, carnivores likely focused on safer meals — juveniles, sick or injured adults, animals trapped in mud, or carcasses left behind by droughts or floods.
To piece together this ancient food web, researchers drew on multiple lines of evidence, including chemical signatures in fossil teeth, microscopic scratches on tooth enamel, biomechanical models and even fossilised stomach contents. The Dry Mesa site, formed during a severe drought, preserved an unusually complete snapshot of the ecosystem. "It's one of the only places where you get everything, from small lizard-like animals to the largest dinosaurs," Morrison said.
At the time, the landscape was dominated by open woodlands of conifers, cycads, ferns and horsetails growing along rivers and shallow ponds that periodically dried out. The resulting food web was astonishingly complex, containing more than 12,000 unique food chains.
Rather than sitting at the top as untouchable giants, sauropods — especially their young — were central to this interconnected system. The findings paint a vivid picture of a Jurassic world where survival depended not just on size, but on timing, vulnerability and the constant balance between predator and prey.
