A new study led by a researcher from UCL (University College London) finds that baby and very young sauropods were critical to sustaining predators during the Late Jurassic. Sauropods were long necked, long tailed plant eaters that grew into the largest animals ever to walk on land, yet their earliest life stages were small, exposed, and highly vulnerable.
The research was published in the New Mexico Museum of Natural History and Science Bulletin and draws on fossil evidence dating back roughly 150 million years. These fossils come from the Morrison Formation in the United States and were used to reconstruct a detailed food web, showing how plants, herbivores, and carnivores were linked through feeding relationships.
The study shows that juvenile sauropods were a major food source for several species of meat eating dinosaurs. These young animals lacked effective defenses and appear to have been left to survive on their own, making them especially easy targets.
Lead author Dr. Cassius Morrison of UCL Earth Sciences explained the contrast between adult size and early vulnerability. He said: "Adult sauropods such as the Diplodocus and Brachiosaurus were longer than a blue whale. When they walked the earth would shake. Their eggs, though, were just a foot wide and once hatched their offspring would take many years to grow.
"Size alone would make it difficult for sauropods to look after their eggs without destroying them, and evidence suggests that, much like baby turtles today, young sauropods were not looked after by their parents.
"Life was cheap in this ecosystem and the lives of predators such as the Allosaurus were likely fueled by the consumption of these baby sauropods."
Much of the data came from the Dry Mesa Dinosaur Quarry in Colorado, a site known for its exceptionally rich fossil record. The quarry preserves remains deposited over a span of up to about 10,000 years and includes at least six species of sauropod (among them a Diplodocus, Brachiosaurus, and Apatosaurus).
To determine who ate whom, the researchers combined multiple lines of evidence. These included body size, patterns of tooth wear, chemical clues such as isotope levels preserved in fossil remains, and in rare cases fossilized stomach contents that revealed an animal's last meal.
Using this information, the team reconstructed the Jurassic food web in greater detail than previously achieved for dinosaurs. They relied on software commonly used to analyze modern ecosystems to map all possible feeding connections among dinosaurs, other animals, and plants.
The analysis showed that sauropods played a central role in the ecosystem. They were connected to far more plants and predators than other major plant eating dinosaurs, particularly the ornithischians (plant-eaters such as the armored Stegosaurus who were more dangerous prey).
Dr. Morrison said: "Sauropods had a dramatic impact on their ecosystem. Our study allows us to measure and quantify the role they had for the first time.
"Reconstructing food webs means we can more easily compare dinosaur ecosystems across different periods. It helps us to understand evolutionary pressures and why dinosaurs might have evolved in the way they did."
The researchers also noted how these dynamics may have influenced later dinosaur evolution. About 70 million years later, during the time of Tyrannosaurus Rex, fewer sauropods were available as easy prey. This change may have driven the evolution of traits such as stronger bite force, larger body size, and improved vision, enabling T. Rex to hunt larger and more dangerous animals like Triceratops, which were armed with three large horns.
William Hart, a co-author from Hofstra University in the United States, said: "The apex predators of the Late Jurassic, such as the Allosaurus or the Torvosaurus, may have had an easier time acquiring food compared to the T. Rex millions of years later.
"Some Allosaurus fossils show signs of quite horrific injuries -- for instance caused by the spiked tail of a Stegosaurus -- that had healed and some which hadn't. But an abundance of easy prey in the form of young sauropods may have allowed injured allosaurs to survive."
The Morrison Formation is a prominent sequence of Upper Jurassic sedimentary rock (approx. 156-147 million years old) spanning 1.5 million square kilometers across the western United States. Known as North America's most fertile source of dinosaur fossils, it contains massive deposits of mudstone, sandstone, and limestone from ancient rivers and floodplains.
The study involved researchers from institutions in the UK, the United States, Canada, and the Netherlands.
