Two recent studies provide new insights into the diets and ecological roles of dinosaurs. The first, focusing on the Late Jurassic Morrison Formation, indicates that juvenile sauropods were a primary prey source for large theropods, shaping the ecosystem's structure. The second, focusing on the Late Cretaceous duck-billed dinosaur Maiasaura peeblesorum, suggests that juveniles and adults consumed different foods, likely due to parental provisioning.
Late Jurassic Food Web and the Role of Juvenile Sauropods
Methodology and Scope
A study conducted by researchers from University College London and Hofstra University, led by Dr. Cassius Morrison, examined the Morrison Formation, specifically the Dry Mesa Dinosaur Quarry in Colorado. The findings are scheduled for publication in the New Mexico Museum of Natural History and Science Bulletin.
To reconstruct the ancient food web, scientists analyzed dinosaur size, tooth wear patterns, bone structure, and chemical analysis of fossilized body fluids. This data was processed using software typically employed for modern ecosystem studies. The Dry Mesa quarry was identified as a unique site because its fossils were deposited over a 10,000-year period, ensuring the animals represented coexisted. The resulting model included nearly 100 ecological nodes and over 700 feeding connections.
Key Findings
- Young sauropods, which hatched from eggs roughly one foot in diameter and were likely not protected by parents, became accessible prey for carnivores such as Allosaurus.
- Juvenile sauropods are presented as a primary food source that influenced the survival of apex predators. Co-author Dr. William Hart from Hofstra University stated that the availability of this prey source may have contributed to the longevity of predators like Allosaurus, even when injured. This contrasts with later predators such as Tyrannosaurus rex, which hunted more heavily armored prey.
- Adult sauropods, such as Diplodocus and Brachiosaurus, grew to immense sizes and had no natural predators.
- Sauropods were central to the ecosystem, influencing plant growth through their feeding and disturbing the land with their movements.
Comparative Analysis
By comparing Late Jurassic food webs with those from other periods, researchers gain insight into evolutionary pressures on dinosaurs. The decline in sauropod species towards the end of the Mesozoic Era is linked to the evolution of larger, stronger-biting predators, such as T. rex, which hunted armored dinosaurs like Triceratops.
The study notes that the Dry Mesa ecosystem exhibits patterns similar to modern open habitats like African savannahs, offering a model for understanding energy flow through ancient systems.
Late Cretaceous Maiasaura Diet and Parental Care
Methodology and Scope
A study published in Palaeogeography, Palaeoclimatology, Palaeoecology analyzed dental wear patterns on fossilized teeth of Maiasaura peeblesorum, a hadrosaur from the Late Cretaceous period (~75–80 million years ago) in Montana.
Key Findings
- Juvenile Maiasaura teeth exhibited more crushing wear.
- Adult Maiasaura teeth exhibited more shearing wear.
- The difference in wear patterns suggests juveniles consumed softer, higher-protein foods (e.g., fruit), while adults consumed tougher, high-fiber plants.
Interpretation
Lead author John Hunter (Ohio State University) stated that this dietary difference likely indicates parents brought food to young confined to the nest, a behavior common in modern birds. The study suggests this parental care behavior may be rooted in the origin of dinosaurs, predating birds.
Other explanations considered include juveniles consuming partially regurgitated food from parents, or foraging independently—a scenario deemed less likely due to the helplessness of hatchlings.
Background
Maiasaura peeblesorum is known from extensive fossil nests, making it a key species for studying reproductive behaviors in duck-billed dinosaurs. The research received support from Brown University. Co-author Christine Janis is affiliated with the University of Bristol and Brown University.