---
title: "Coastal dinosaurs probably ate seaweed 100 million years ago; tooth enamel holds a marine carbon signal"
url: https://badiyaa.com/dinosaurs-seaweed-tooth-enamel-cretaceous/
published: 2026-11-15T11:57:00+00:00
modified: 2026-11-15T11:57:00+00:00
section: Science
publisher: Badiyaa
---

# Coastal dinosaurs probably ate seaweed 100 million years ago; tooth enamel holds a marine carbon signal

Dinosaurs on North America's Cretaceous coasts probably ate seaweed, a tooth-enamel carbon study led by the University of Arkansas finds.

Plant-eating dinosaurs living on North American coastlines about 100 million years ago were probably eating seaweed, according to carbon locked in their tooth enamel. Coastal teeth carry a carbon signal as much as 5.5 parts per thousand higher than a land-plant diet should leave, a gap that shows up in fish, crocodile relatives and dinosaurs alike but disappears inland.

The study, titled “[Marine subsidization of dinosaurian ecosystems](https://doi.org/10.3389/fevo.2026.1895247),” appeared in Frontiers in Ecology and Evolution. Its first author is Clayton Forster, a geologist at the University of Arkansas, working with colleagues at Auburn University, North Carolina State University and the North Carolina Museum of Natural Sciences.

## How carbon in teeth records a menu

Carbon comes in a light form, carbon-12, and a heavy form, carbon-13. Food leaves its ratio of the two in an animal’s enamel, shifted upward by a predictable amount. Seaweeds and other marine plants run richer in carbon-13 than most land plants, so an animal topping up its diet from the sea should show a heavier signal.

Paleontologists had long noticed that dinosaur teeth from the Cretaceous often read “too heavy” for animals eating ordinary land plants. Forster’s team set out to test whether the ocean was the missing ingredient.

They powdered enamel from fossils in deposits that once lined the Western Interior Seaway, the inland sea that split North America in two, and the ancient Gulf of Mexico shore. At its widest, [that seaway](https://en.wikipedia.org/wiki/Western_Interior_Seaway) ran about 970 kilometers (600 miles) across and more than 3,200 kilometers (2,000 miles) from end to end, which gave dinosaurs an enormous length of beach. Sites ranged from the Dunvegan Formation of British Columbia and Alberta to the Antlers and Woodbine formations of Oklahoma and Texas and the Mussentuchit Member in Utah. For an inland control, they used the Cloverly Formation of Wyoming and Montana. The fossils date to two windows: roughly 113 to 107 million years ago and roughly 100 to 96 million years ago.

## What the teeth showed

Coastal animals came out consistently heavier than inland ones, and the coastal values held steady across latitude and across both time windows. Because the boost appeared from fish all the way up to giant plant-eaters, the extra carbon had to enter near the bottom of the food chain.

“Few organisms meet these criteria besides marine macroalgae or macrophytes – seaweeds,” Forster said in a statement released through the journal’s publisher.

Think of it as the Cretaceous version of a modern storm beach. Today, deer, sheep and other coastal grazers browse kelp washed ashore, and ecologists call that flow of ocean food onto land marine subsidization. The paper argues the same link already existed when sauropods and duck-billed relatives roamed the shoreline.

One species broke the pattern. Tenontosaurus tilletti, a big plant-eater pictured above in a museum mount, had enamel values in line with a purely land-based diet. That variation matters to the authors: if burial chemistry had altered the teeth, every species would be skewed the same way.

## Limits

No specimens from polar or equatorial sites of the same age were available, so the reach of the behavior is unknown. The study also covers only two slices of the Cretaceous; the Jurassic and the early Cenozoic are untested. And the isotope signal points to a marine source low in the food chain, not to a fossilized mouthful of seaweed, so “probably ate seaweed” is an inference from chemistry.

The finding has a practical knock-on. Earlier studies that worked backward from dinosaur enamel to estimate ancient plant chemistry left marine carbon out, and the authors say those estimates now need revisiting.

The coastal setting is the same Cretaceous sea world that produced the giant marine lizard [Prognathodon currii, whose skull tops 1.4 meters](https://badiyaa.com/prognathodon-currii-mosasaur-skull-israel/), and a new [fossil treasure map of ancient shallow seas](https://badiyaa.com/fossil-treasure-map-shallow-sea-cenozoic/) shows how much of that record is still unexplored.

## Further reading

- [Paper: Marine subsidization of dinosaurian ecosystems](https://doi.org/10.3389/fevo.2026.1895247)

- [Wikipedia: Western Interior Seaway](https://en.wikipedia.org/wiki/Western_Interior_Seaway)

*Image: Rodney, CC BY 2.0 via Wikimedia Commons*

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