A new study reveals that young sauropods, despite their parents' massive size, were vulnerable prey that sustained Late Jurassic predators. Researchers from UCL analyzed fossils from Colorado's Dry Mesa Quarry to reconstruct the era's food web. This abundance of easy meals may explain why predators like Allosaurus thrived without advanced hunting traits.
In the Late Jurassic period, approximately 150 million years ago, the Morrison Formation in the western United States teemed with life, as evidenced by fossils from the Dry Mesa Dinosaur Quarry in Colorado. This site, preserving remains over about 10,000 years, yielded bones from at least six sauropod species, including Diplodocus, Brachiosaurus, and Apatosaurus. Sauropods, the long-necked herbivores that grew longer than blue whales, dominated the landscape, but their juveniles were small and defenseless.
Lead author Dr. Cassius Morrison of UCL Earth Sciences highlighted the stark contrast: "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." Evidence suggests parents did not care for the young, similar to modern sea turtles, leaving them exposed to predators like Allosaurus and Torvosaurus.
Using body sizes, tooth wear patterns, isotope analysis, and occasional stomach contents, the team mapped the food web with ecosystem modeling software. Sauropods connected to more plants and predators than other herbivores, such as the armored Stegosaurus. Dr. Morrison noted: "Sauropods had a dramatic impact on their ecosystem. Our study allows us to measure and quantify the role they had for the first time."
This steady supply of juvenile sauropods likely eased predation pressures. Co-author William Hart from Hofstra University observed: "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." By the time of Tyrannosaurus rex, about 70 million years after, scarcer easy prey may have spurred evolutions like stronger bites to tackle horned dinosaurs like Triceratops.
The findings, published in the New Mexico Museum of Natural History and Science Bulletin, involved collaborators from the UK, US, Canada, and Netherlands, offering insights into dinosaur evolution and ecosystem dynamics.