Dinosaurs Were Beachcombers, Fossil Study Reveals Seafood Snacking

A team of paleontologists has found evidence that dinosaurs were not strictly land-bound eaters but rather opportunistic foragers who supplemented their diets with seafood washed ashore by storms—a survival strategy that modern coastal animals still employ today. The discovery emerged from an analysis of carbon isotope signatures preserved in fossilized teeth and bones, a chemical fingerprint that reveals what ancient creatures actually consumed millions of years ago.

The research, led by Clayton Forster, a geologist at the University of Arkansas, focused on a puzzle that had long troubled scientists studying dinosaur remains. When researchers measured the carbon isotope ratios in dinosaur tooth enamel, the values were consistently higher than expected for animals eating only land plants. Land plants contain lower ratios of the heavier carbon isotope (C-13) compared to marine plants, so if dinosaurs were purely terrestrial herbivores, their teeth should reflect that signature. Instead, the chemical fingerprints suggested something else was happening—something that pointed toward the ocean.

Forster and his team tested a hypothesis: what if dinosaurs and their prey were eating marine matter that storms regularly deposited on beaches? This process, called marine subsidization, is well-documented in modern ecosystems. Coastal animals from deer to bears routinely supplement their diets with kelp, fish, and other marine organisms cast ashore. To investigate whether dinosaurs did the same, the researchers analyzed fossils from coastal sites along what was once the Western Interior Seaway—a vast inland sea that divided North America roughly 100 million years ago—as well as from ancient Gulf of Mexico coastlines. They compared these coastal specimens with fossils from landlocked sites, all dating to the early Cretaceous period between 113 and 96 million years ago.

The results were striking and consistent. Fossils from coastal sites showed significantly higher carbon isotope values than those from inland locations, and this pattern held true across different latitudes and time periods. The signature appeared in the remains of fish, crocodiles, turtles, and dinosaurs alike, suggesting that marine resources were entering the food chain at a fundamental level and moving upward through predators and prey. The most likely source, Forster explained, was seaweed. Few organisms meet the criteria of being abundant in coastal but not inland habitats, available across millions of years, and capable of affecting both aquatic and terrestrial animals in the food web. Marine macroalgae fit perfectly.

Not every dinosaur relied on this strategy, however. Tenontosaurus tilletti, a large herbivorous dinosaur found across many Cretaceous sites, showed carbon isotope values consistent with animals today that eat only land plants. This variation suggests that dietary preferences, not geological processes, account for the differences observed in the fossil record. Some dinosaurs exploited marine resources when available; others apparently did not.

The findings carry implications beyond dinosaur diets. They demonstrate that terrestrial and marine ecosystems have been deeply interconnected for hundreds of millions of years, with energy and nutrients flowing between them in ways that shaped the survival of ancient species. Forster emphasized that this connection persists today, underscoring why protecting the linkages between coastal and ocean environments matters now. The research also identifies a significant gap: the dataset lacks information from polar and equatorial regions during the periods studied, leaving open the question of whether marine subsidization was equally important for dinosaurs across all latitudes and climates. Future work will need to examine whether this dietary strategy extended into earlier periods like the Jurassic or later into the early Cenozoic era.