More than a hundred million years before the first human walked a shoreline, dinosaurs were doing what coastal creatures have always done: turning to the sea when the land offered less than enough. A new study published in Frontiers in Ecology and Evolution finds chemical signatures locked in fossilized teeth suggesting that Cretaceous dinosaurs along ancient North American coasts consumed marine seaweed washed ashore, a survival strategy ecologists recognize in animals today. The discovery, rooted in carbon isotope analysis spanning multiple species and sites, reveals that the bond between oc
Cretaceous dinosaurs supplemented diets with seaweed, fossil teeth reveal
Dinosaurs and their prey ate seaweed washed ashore, just as coastal animals do today.
Mark
So dinosaurs ate seaweed? That's surprising. How do we actually know that from teeth?
Mimi
The teeth contain a chemical signature—a ratio of carbon isotopes that reflects what the animal ate. When you eat something, that signature gets locked into your tooth enamel. The researchers found that coastal dinosaur teeth had a different signature than inland dinosaurs.
Luke
But wait—how do they know the signature came from seaweed specifically, and not some other marine source?
Mimi
That's the reasoning Forster lays out. Seaweed is the only organism that fits all the criteria: it lives in coastal but not inland habitats, it's been around for millions of years, and it's abundant enough to affect the whole food chain.
Mark
So they're inferring seaweed because it's the best explanation, not because they found seaweed in the teeth?
Mimi
Exactly. They're working backward from the chemical pattern.
Luke
And how confident are we in the isotope measurements themselves? Could geological processes after death have altered the enamel?
Mimi
The researchers tested that by comparing coastal and inland sites. If geological processes were the culprit, you'd expect the pattern to be random. Instead, it's consistent across all coastal sites but absent in landlocked ones.
Mark
So the pattern is real, but we're still inferring the source.
Luke
Right. And there's another thing—they didn't sample everywhere. No polar or equatorial sites from that time period. So we don't know if this was happening globally or just in certain regions.
Mimi
That's exactly why they're calling for more research. This is the first study to identify the pattern at all.
Mark
What about that one dinosaur that didn't show the signal?
Mimi
Tenontosaurus tilletti. Its teeth looked like a pure land-plant eater. So not all dinosaurs were doing this.
Luke
Which actually strengthens the case that it's a dietary choice, not something forced on them by the environment.
Mimi
Yes. Some species exploited the resource when they lived near the coast; others didn't.
The Pulse
- Fossilized dinosaur teeth are carrying isotopic values that simply cannot be explained by a diet of land plants alone — something marine was entering the food chain.
- The anomaly appears consistently across coastal sites bordering the ancient Western Interior Seaway and Gulf of Mexico, but vanishes entirely at landlocked formations, ruling out geological contamination.
- Fish, crocodiles, turtles, and dinosaurs all show the elevated carbon signature, meaning marine seaweed wasn't a fringe snack — it was moving through entire prehistoric food webs.
- Not every dinosaur followed the pattern: Tenontosaurus tilletti showed no marine signal, suggesting this was a behavioral choice some species made and others did not.
- Researchers have confirmed the pattern for 113 to 96 million years ago but acknowledge polar, equatorial, and other geological periods remain unmapped, leaving the full scope of this ancient connection still open.
More than a hundred million years before the first human walked a shoreline, dinosaurs were doing what coastal creatures have always done: turning to the sea when the land offered less than enough. A new study published in Frontiers in Ecology and Evolution finds chemical signatures locked in fossilized teeth suggesting that Cretaceous dinosaurs along ancient North American coasts consumed marine seaweed washed ashore, a survival strategy ecologists recognize in animals today. The discovery, rooted in carbon isotope analysis spanning multiple species and sites, reveals that the bond between ocean and land is not a modern convenience but an ancient, enduring arrangement written into the chemistry of life itself.
When storms push seaweed onto modern beaches, land animals eat it. Ecologists call this marine subsidization — the ocean feeding the shore. A new study in Frontiers in Ecology and Evolution argues that dinosaurs were doing the same thing more than 100 million years ago.
The evidence lives inside fossilized teeth. Plants absorb atmospheric carbon in two isotopic forms, and the ratio between them — δ13C — acts as a chemical fingerprint that travels up the food chain into tooth enamel. When Dr. Clayton Forster of the University of Arkansas and his team examined Cretaceous dinosaur teeth, the enrichment values were consistently higher than what land plants alone could produce. Something with a marine isotopic signature had entered the diet.
To test their hypothesis, the researchers compared tooth enamel from fossils collected along the ancient Western Interior Seaway and Gulf of Mexico coastlines against samples from landlocked sites. The coastal fossils — spanning roughly 113 to 96 million years ago — showed reliably higher δ13C values. The pattern held across fish, crocodiles, turtles, and dinosaurs alike, suggesting marine resources were moving through entire food webs rather than being consumed by a single opportunistic species.
Seaweed emerged as the most plausible culprit. Marine macroalgae are coastal but not inland, abundant, and persistent across geological time — and large herbivores today routinely supplement their diets with it. Not every dinosaur in the study followed the pattern, however: Tenontosaurus tilletti showed values consistent with a purely terrestrial diet, indicating that marine subsidization was a choice, not a universal necessity.
The study marks the first identification of marine subsidization in a prehistoric ecosystem. Gaps remain — polar and equatorial regions are unexamined, and other geological periods await analysis — but the core finding is clear: the entanglement of land and sea is not a recent ecological novelty. It is an ancient relationship, written in the teeth of creatures that walked the earth long before we arrived to name them.
When storms batter a coastline today, they deposit seaweed and other marine debris onto beaches where land animals find it and eat it. Ecologists call this marine subsidization—the way ocean resources feed terrestrial creatures, especially when droughts or other pressures make land-based food scarce. A new study published in Frontiers in Ecology and Evolution suggests that dinosaurs living along ancient North American coasts relied on this same survival strategy more than 100 million years ago.
The evidence comes from an unexpected source: the chemistry locked inside fossilized teeth. Plants absorb carbon from the atmosphere in two forms—the lighter isotope C-12 and the heavier C-13. The ratio between them, measured as δ13C, acts like a chemical fingerprint that travels up the food chain. When an animal eats, that isotopic signature gets incorporated into its tooth enamel. In modern animals, the enamel shows a predictable enrichment of about 11 to 13 parts per thousand compared to the food itself. But when researchers examined dinosaur teeth, the enrichment was consistently higher than this expected range. The teeth also showed δ13C values too high to match animals eating only land plants, which contain less of the heavy isotope than marine vegetation does. Something was off, and the mystery demanded explanation.
Dr. Clayton Forster, a geologist at the University of Arkansas and lead author of the study, and his team hypothesized that coastal dinosaurs and their prey were consuming marine material washed ashore. To test this, they analyzed tooth enamel from fossils collected at sites that once bordered the Western Interior Seaway—a vast inland sea that divided North America into two separate landmasses around 100 million years ago—as well as from ancient Gulf of Mexico coastlines. They also sampled teeth from landlocked sites far from any ocean. The fossils ranged from the early Albian period, roughly 113 to 107 million years ago, through the early Cenomanian, approximately 100 to 96 million years ago.
The results were striking. Fossils from coastal sites consistently showed higher δ13C values than those from inland formations. This pattern held true regardless of latitude or age—a remarkable consistency that suggested a real dietary choice rather than some geological process that altered the chemical composition after death. The signal appeared in fish, crocodiles, turtles, and dinosaurs alike, indicating that marine resources were being passed through the entire food web, from the smallest consumers to the largest herbivores.
Forster and his colleagues concluded that the most likely source was seaweed. Few organisms meet the criteria: they must live in coastal but not inland habitats, remain available across millions of years, and be abundant enough to influence the isotopic signature of both aquatic and terrestrial animals. Marine macroalgae fit perfectly. The finding aligns with modern behavior—large coastal herbivores today routinely supplement their diets with seaweed, and there is no reason to think Cretaceous dinosaurs would have behaved differently when the same resource was available.
Not every dinosaur in the study showed this pattern. Tenontosaurus tilletti, a large herbivorous dinosaur found across many Cretaceous sites, displayed δ13C values consistent with animals eating only land plants. This variation suggests that marine subsidization was a dietary choice, not a universal necessity. Some species exploited it; others did not.
The study represents the first clear identification of marine subsidization in a prehistoric ecosystem, but significant gaps remain. The researchers lacked data from polar and equatorial regions during the periods they examined, and they have not yet determined whether this pattern extended to other geological eras, such as the Jurassic Period before the Cretaceous or the early Cenozoic that followed. Forster emphasized that the work underscores how deeply terrestrial and marine ecosystems have been intertwined across hundreds of millions of years—a connection that future research will need to map more completely across time and geography.
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
They are deeply intertwined and have been for hundreds of millions of years. It highlights the importance of environmental linkages across time and space and protecting them where they exist today.— Dr. Clayton Forster, on terrestrial and marine ecosystem connections
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