Long before modern seabirds learned to scavenge the tide line, creatures of the Cretaceous coastline were doing the same. A new isotopic study of fossilized dinosaur teeth reveals that, some 100 million years ago, coastal dinosaurs and their prey supplemented their diets with marine matter — seaweed and ocean-washed organic material — much as today's coastal animals exploit the sea's generosity after storms. The findings, published in Frontiers in Ecology and Evolution, remind us that the boundary between land and ocean has never been a wall, but a threshold crossed by the hungry across deep t
Dinosaurs Supplemented Diets With Seafood, Fossil Study Reveals
Dinosaurs grazed on seaweed washed ashore by ancient storms
Mark
So the researchers looked at the chemistry of dinosaur teeth and found evidence of seaweed in their diet. How exactly does that work?
Mimi
They measured the ratio of two carbon isotopes—C-12 and C-13—in the tooth enamel. That ratio acts like a fingerprint of what an animal ate. Marine plants have a different isotopic signature than land plants, so when you see that marine signature in a dinosaur's teeth, you know it ate something from the ocean.
Luke
But wait—couldn't that signature have changed after the animal died, during fossilization? How do they rule that out?
Mimi
Good question. They compared dinosaurs from coastal sites to ones from inland sites, and they also looked at Tenontosaurus, which showed only land-plant signatures. If fossilization was changing the chemistry, you'd expect all dinosaurs to show the same pattern. They don't.
Mark
And they found this pattern across different time periods and different coastal regions?
Mimi
Yes. Fossils from the Western Interior Seaway and the Gulf of Mexico coastline, from two different geological ages, all showed the same elevated isotope ratios. That consistency across space and time suggests a real dietary behavior, not a random chemical artifact.
Luke
What's the actual evidence that it was seaweed specifically, though? The paper says seaweed is the most likely source, but did they rule out other marine organisms?
Mimi
They reasoned through it: the carbon source had to be available only in coastal habitats, not inland, and it had to persist for millions of years. Seaweed fits. Other marine organisms—fish, plankton—don't live in the same way or wouldn't be as consistently available to land animals.
Mark
So dinosaurs were basically doing what modern coastal animals do—grabbing a snack from the beach when storms washed things ashore.
Mimi
Exactly. And it wasn't just the dinosaurs themselves. The isotopic signature appears in fish and crocodiles too, suggesting the entire coastal food web was tapping into marine resources.
Luke
One thing I'd want to know: how much of their diet was actually seaweed? The study shows they ate some, but does it tell you whether it was a major food source or just occasional supplementation?
Mimi
That's a limitation the researchers acknowledge. They can identify that marine resources were incorporated into the food chain, but quantifying the proportion is harder. That's work for future studies.
Mark
And they haven't looked at polar or equatorial regions yet, or earlier time periods?
Mimi
Right. The data they have is from specific latitudes during the early Cretaceous. Whether this behavior was common everywhere, or just in certain climates, remains an open question.
The Pulse
- Carbon isotope ratios locked inside fossilized tooth enamel were running higher than any land-only diet could explain, pointing scientists toward an unexpected dietary secret.
- The anomaly appeared consistently across coastal fossil sites spanning the Western Interior Seaway and the ancient Gulf of Mexico — regardless of latitude or geological age — suggesting this was no local quirk but a widespread behavioral pattern.
- Researchers tested the hypothesis by comparing coastal and inland fossil specimens from two distinct Cretaceous time windows, using fish, crocodiles, and dinosaurs alike as chemical witnesses to ancient meals.
- Seaweed emerged as the most plausible culprit: a marine food source available only at coastlines, persistent across millions of years, and already known to supplement the diets of large herbivores in modern coastal ecosystems.
- The herbivore Tenontosaurus, found at both coastal and inland sites, showed isotopic values consistent with a purely terrestrial diet — confirming that the elevated signatures in other specimens reflect real dietary choices, not post-burial chemistry.
- The study marks the first documented case of marine subsidization in a prehistoric ecosystem, opening new questions about how far back — and how broadly — this land-sea feeding connection extends through Earth's history.
Long before modern seabirds learned to scavenge the tide line, creatures of the Cretaceous coastline were doing the same. A new isotopic study of fossilized dinosaur teeth reveals that, some 100 million years ago, coastal dinosaurs and their prey supplemented their diets with marine matter — seaweed and ocean-washed organic material — much as today's coastal animals exploit the sea's generosity after storms. The findings, published in Frontiers in Ecology and Evolution, remind us that the boundary between land and ocean has never been a wall, but a threshold crossed by the hungry across deep time.
When storms roll in off the ocean today, they leave behind a bounty — seaweed, organic debris, the sea's overflow onto land. Coastal animals have always known to take advantage of it. Scientists call this marine subsidization. Now, a study published in Frontiers in Ecology and Evolution suggests dinosaurs were doing it too, reading the tide line for food during the Cretaceous Period.
The evidence is chemical. Plants carry two forms of carbon — a lighter isotope, C-12, and a heavier one, C-13 — and the ratio between them acts as a dietary fingerprint, preserved in tooth enamel long after an animal dies. When researchers examined Cretaceous dinosaur teeth, they found isotopic shifts larger than a land-only diet could produce. The carbon-13 ratios pointed toward marine vegetation as a supplementary food source.
Lead author Dr. Clayton Forster of the University of Arkansas and his team tested this by comparing fossils from coastal sites — along the ancient Western Interior Seaway and the Gulf of Mexico shoreline — against specimens from inland formations. Across two separate time windows spanning roughly 113 to 96 million years ago, the pattern held: coastal fossils consistently showed higher δ13C values than inland ones. The consistency across different latitudes and geological ages pointed to a single, durable source. Seaweed fit best.
Not every dinosaur showed the pattern. Tenontosaurus tilletti, a widespread herbivore, displayed isotopic values in line with a purely terrestrial diet — a crucial control confirming that the elevated signatures elsewhere reflect genuine behavior, not post-burial contamination. Some dinosaurs foraged the coast; others did not.
The study is the first to identify marine subsidization in a prehistoric ecosystem. Gaps remain — polar and equatorial regions are unsampled, and earlier periods like the Jurassic await investigation — but the broader implication is already clear: land and sea have been feeding each other's creatures for hundreds of millions of years, and the ecological threads connecting them are older, and more fragile, than we often recognize.
When storms batter a coastline today, they deposit organic matter from the sea onto beaches and shores. Seabirds, crabs, and coastal mammals have learned to exploit this windfall. Scientists call it marine subsidization—the way ocean resources supplement the diets of land-dwelling creatures when terrestrial food grows scarce. A new study published in Frontiers in Ecology and Evolution suggests that dinosaurs, too, took advantage of this ancient food source, consuming seaweed and other marine matter that washed ashore during the Cretaceous Period.
The evidence lies in the chemistry of fossilized teeth. Plants contain two forms of carbon—a lighter isotope called C-12 and a heavier one, C-13. The ratio between them, measured as δ13C, acts like a chemical fingerprint that passes from food into the bodies of animals that eat it. When an animal consumes food, that isotopic signature gets locked into the enamel of its teeth, though the ratio shifts slightly upward in a predictable way. In modern animals, this shift ranges between 11 and 13 parts per thousand. But when researchers examined dinosaur teeth, they found the shift was consistently larger than expected. The δ13C values were also higher than what would result from eating only land plants, which have lower isotopic ratios than marine vegetation. The mystery suggested that dinosaurs or their prey had been eating something from the ocean.
Dr. Clayton Forster, a geologist at the University of Arkansas and lead author of the study, and his team set out to test this hypothesis. They collected fossils from sites that were once coastal—along the ancient Western Interior Seaway, a vast inland sea that split North America into two landmasses roughly 100 million years ago, and from the ancient Gulf of Mexico shoreline. They also sampled fossils from inland sites for comparison. The specimens came from two time periods: the early Albian, around 113 to 107 million years ago, and the early Cenomanian, approximately 100 to 96 million years ago. By analyzing the isotopic composition of tooth enamel from dinosaurs, fish, crocodiles, and other creatures, the researchers could determine what these animals had actually eaten and whether their diets differed between coastal and inland regions.
The results were striking. Fossils from coastal sites showed consistently higher δ13C values than those from landlocked formations. More importantly, this pattern held true across different coastal sites, regardless of latitude or the age of the fossils. The consistency suggested a single dietary source shared across a vast region and spanning millions of years. Forster explained that the carbon had to come from something in the ocean, or from prey that had consumed it. The source also had to be available only in coastal habitats, not inland, and had to persist across geological time. Few organisms fit these criteria. Seaweed—marine macroalgae—emerged as the most likely culprit. Large herbivorous dinosaurs today's coastal animals often supplement their diets with kelp and other seaweeds, and the fossil evidence suggests Cretaceous herbivores did the same.
Yet not every dinosaur relied on marine resources. Tenontosaurus tilletti, a large herbivore found across many Cretaceous sites, showed δ13C values consistent with animals that eat only land plants. This finding matters because it demonstrates that the higher isotopic signatures in other dinosaur teeth reflect genuine dietary choices rather than chemical changes that occurred after the animals died. Some dinosaurs were coastal foragers; others were not. The study marks the first time researchers have identified marine subsidization in prehistoric ecosystems, revealing that the connection between land and sea has shaped animal behavior for hundreds of millions of years.
Forster and his colleagues acknowledge gaps in their work. They lack data from polar and equatorial regions during the periods they studied, and they have not yet examined whether marine subsidization was common in earlier periods like the Jurassic or later in the Cenozoic. Future research will need to map how widespread this behavior was across different climates and time periods. But the findings already underscore something fundamental: terrestrial and marine ecosystems have always been intertwined. The storms that wash seaweed ashore today were washing it ashore when dinosaurs roamed the coasts. Understanding these ancient connections matters not only for paleontology but for recognizing how modern ecosystems depend on the same linkages—and how fragile those connections can be.
Notable Quotes
Coastal terrestrial organisms in the greenhouse climates of the Cretaceous relied on marine resources to supplement their diets in a similar way that modern organisms do.— Dr. Clayton Forster, University of Arkansas
Terrestrial and marine ecosystems are deeply intertwined and have been for hundreds of millions of years.— Dr. Clayton Forster
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