Dinosaurs living near the coast may have supplemented their diets with food from the sea. New research suggests that marine resources entered Cretaceous food webs and were consumed by dinosaurs and other vertebrates. Research suggests that some herbivorous dinosaurs ate seaweed.

Scientists examined the chemical composition of fossil teeth and bones. They found evidence that marine-derived nutrients were incorporated into terrestrial food chains. Remarkably, the researchers conclude that some herbivorous dinosaurs may even have eaten seaweed washed ashore. The study provides new insights into the complex ecosystems that existed along the shores of the Western Interior Seaway and the ancient Gulf of Mexico during the Cretaceous.

Dinosaurs and Marine Food Resources

Storms regularly wash seaweed, animals and other organic material onto modern beaches. Terrestrial animals often take advantage of this readily available food. Scientists refer to the movement of nutrients and energy from marine environments into terrestrial ecosystems as marine subsidisation. Indeed, our own species Homo sapiens has a long history of beachcombing.  Early modern humans in South Africa for example, are thought to have survived severe climate change by relying on scouring the shoreline to supplement their diet.

Researchers wanted to discover whether the similar behaviours were exhibited by animals that lived during the Mesozoic.

Dr Clayton W. Forster of the University of Arkansas and colleagues studied the stable carbon isotope composition preserved in fossil material. Their research was published in the journal “Frontiers in Ecology and Evolution Paleoecology”.

The scientists concluded that marine resources probably made an important contribution to several coastal Cretaceous ecosystems.

Dr Forster explained:

“We show that 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.”

Marine-derived resources could move through the entire food chain. Therefore, an animal did not necessarily have to eat seaweed or other marine material directly to acquire its chemical signature.

Theropod tooth from the Mussentuchit Member assemblage on a foam block next to a scale card. Chemical analysis of fossil teeth can provide evidence about the food consumed by animals millions of years ago. Picture credit: North Carolina Museum of Natural Sciences/Clayton Forster.

Picture credit: North Carolina Museum of Natural Sciences/Clayton Forster

Chemical Fingerprints Preserved in Dinosaur Teeth

The researchers focused particularly on different isotopes of carbon. Carbon occurs naturally in several forms, including carbon-12 and carbon-13. The ratio between these isotopes can provide scientists with information about diet. Importantly, this chemical signal can become incorporated into tooth enamel.

Marine plants tend to have higher carbon isotope values than plants growing on land. Consequently, animals consuming marine vegetation, or eating animals that had exploited marine resources, can acquire a distinctive carbon isotope signature. Scientists had previously encountered unexpectedly high carbon isotope values in Cretaceous vertebrate fossils. The new study offers a possible explanation.

The team analysed fossil material from several formations representing ancient coastal environments. These included the Antlers, Woodbine, Dunvegan and Wayan formations, along with the Mussentuchit Member of the Cedar Mountain Formation. These deposits were associated with the margins of the Western Interior Seaway or the ancient Gulf of Mexico.

For comparison, fossils from the predominantly inland Cloverly Formation were also studied.

The Western Interior Seaway

During parts of the Cretaceous, rising sea levels flooded enormous areas of North America. The Western Interior Seaway eventually divided the continent into western and eastern landmasses (Laramidia and Appalachia). Dinosaurs living close to its shores inhabited environments very different from those of dinosaurs living farther inland. The study examined fossil assemblages dating from the Early to early Late Cretaceous. The researchers identified a consistent difference between coastal and inland ecosystems. Fossils from coastal environments generally possessed higher carbon isotope values. This pattern was detected across different animals and locations. It also occurred at sites of different geological ages.

The scientists interpret this as evidence that marine-derived nutrients were entering terrestrial food webs.

A large crocodilian tooth from the Wayan Formation. The Wayan Formation was one of several deposits included in the study of marine-derived nutrients in Cretaceous ecosystems. The specimen is shown next to a centimetre ruler in a specimen box on top of its specimen information card. Picture credit: Idaho Museum of Natural History/Clayton Forster.

Picture credit: Idaho Museum of Natural History/Clayton Forster

Did Dinosaurs Eat Seaweed?

Perhaps the most intriguing question concerns the source of the marine carbon. Dr Forster and his colleagues suggest that marine macroalgae and aquatic plants are strong candidates. The chemical signature occurred in animals occupying different parts of the food web. Therefore, the original source was probably situated relatively low down in the ecosystem.

Seaweed fits this hypothesis extremely well.

Large herbivorous mammals living near coastlines today sometimes eat seaweed. It provides a useful supplementary food source, particularly when terrestrial vegetation becomes scarce.

The researchers propose that coastal herbivorous dinosaurs may have behaved in a similar way.

Dr Forster added:

“Few organisms meet these criteria besides marine macroalgae or macrophytes – seaweeds.”

If herbivorous dinosaurs consumed washed-up seaweed, the marine-derived carbon could subsequently have passed to predatory dinosaurs when they ate these herbivores. Therefore, the research does not necessarily imply that theropod dinosaurs regularly hunted marine animals. Instead, marine nutrients could have moved through a complicated network of ecological relationships.

Not Every Dinosaur Ate Marine-derived Food

Intriguingly, the researchers also discovered evidence of dietary selectivity. Tenontosaurus tilletti was a large herbivorous dinosaur known from several Lower Cretaceous formations of North America. The carbon isotope values associated with the Tenontosaurus material examined were consistent with animals feeding primarily on terrestrial vegetation. The researchers concluded that T. tilletti apparently preferred non-marine food resources, although relatively few specimens were available for analysis.

Tenontosaurus tilletti illustration. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

This is an important observation. It suggests that the unusual chemical signatures were associated with diet rather than simply being the result of geological processes altering the fossils after burial.

A Tenontosaurus tilletti tooth from the Cloverly Formation assemblage in a glass sample vial. This ornithopod appears to have preferred terrestrial vegetation rather than marine-derived food. Picture credit: Sam Noble Oklahoma Museum of Natural History/Clayton Forster.

Picture credit: Sam Noble Oklahoma Museum of Natural History/Clayton Forster

Analysing a Cretaceous Food Web

The Cloverly Formation fossils provided an important comparison with the coastal assemblages. The study included teeth from dinosaurs and crocodilians as well as material from other vertebrates. Some specimens were destructively sampled so that their isotopic composition could be determined.

The results indicate that the predominantly inland Cloverly ecosystem lacked the widespread marine influence identified in the coastal deposits.

However, the picture was not entirely straightforward. One gar specimen from the Cloverly Formation preserved chemical evidence suggesting a connection with a marine or estuarine environment. This hints at just how complex interactions between freshwater, marine and terrestrial ecosystems could have been.

Five fossil teeth specimens from the Cloverly Formation assemblage after destructive sampling for isotopic composition and laser ablation analysis. The specimens from left to right are three specimens of crocodilian teeth, the fourth tooth is a Deinonychus antirrhopus tooth, and, finally, on the far right is a Sauropelta edwardsi tooth. The specimens are mounted on adhesive putty attached to a glass slide with specimen labels below them. Picture credit: Sam Noble Oklahoma Museum of Natural History/Clayton Forster.

Picture credit: Sam Noble Oklahoma Museum of Natural History/Clayton Forster

Reconstructing Ancient Dinosaur Dominated Ecosystems

The research demonstrates that palaeontologists need to consider connections between terrestrial and marine habitats when reconstructing ancient ecosystems. Coastlines are dynamic, ever-changing environments. Nutrients move between land and sea, storms deposit organic material on beaches and animals exploit whatever food resources become available.

The same processes appear to have been operating millions of years ago. Furthermore, marine resources might have become especially important during periods when terrestrial food was scarce. Modern coastal ecosystems demonstrate how marine-derived nutrients can help support terrestrial communities.

The researchers conclude that marine macroalgae and other marine plants may have represented important alternative food resources for coastal dinosaurs. This could also help palaeontologists interpret unusual carbon isotope values identified in other Cretaceous fossils.

The First Study of Marine Subsidisation in Mesozoic Terrestrial Ecosystems

The study represents the first identification of marine subsidisation in prehistoric terrestrial ecosystems. Further research could establish how widespread the phenomenon was at other latitudes and during different intervals of geological time.

Dr Forster summarised the wider significance of the research:

“Our study emphasises the connections between terrestrial and marine ecosystems.”

Dinosaurs are often reconstructed as inhabitants of forests, floodplains and river systems. However, this study provides a reminder that many species also lived close to enormous inland seas. Some of these dinosaurs may have wandered along Cretaceous shorelines exploiting whatever the tides and storms brought onto the beach. Intriguingly, studies of trackways found in Jurassic-aged sediments on the Scottish island of Skye indicate the presence of sauropods in coastal environments.  It had been suggested that the relatively open beach environments acted as migration routes for these large herbivores. After all, moving along the coast would have been easier than moving through a dense forest landscape. However, these habitats with their abundant seaweeds being washed up with the tide could have provided plant-eating dinosaurs with a substantial food resource.

To read more about the remarkable sauropod trace fossils on the Isle of Skye: Isle of Skye Sauropods and their Watery World.

For herbivorous dinosaurs at least, that could sometimes have meant adding a little seaweed to the menu.

The scientific paper: “Marine subsidization of dinosaurian ecosystems” by Clayton W. Forster, Celina A. Suarez, Thomas M. Cullen, Lindsay E. Zanno and Ethan G. Hyland published in Frontiers in Ecology and Evolution Paleoecology.

Link: The Scientific Paper.

A new species of large tyrannosaur has been named and described from fossils found in Alberta (Canada). The new theropod, Tromerosaurus solumons, lived around 76 million years ago (Campanian faunal stage of the Late Cretaceous). Intriguingly, this predator possessed a mixture of anatomical characteristics associated with two major tyrannosaurid lineages.

The study could change our understanding of tyrannosaur evolution. It suggests that important tyrannosaurid lineages may have diverged later and evolved more rapidly than previously thought. Mark J. Powers of the University of Alberta, lead author of the paper, assisted Everything Dinosaur in the compilation of this article by providing images.  The study has been published in the “Journal of Vertebrate Paleontology”.

Tromerosaurus attacks a pair of juvenile Brachylophosaurus. Picture credit: Henry Sharpe.

Picture credit: Henry Sharpe

Introducing Tromerosaurus solumons

In 2010, a partial tyrannosaur skeleton was discovered in exposures associated with the upper Oldman Formation of Alberta. The University of Alberta mounted two expeditions (2010 and 2011 field seasons) to recover the skeleton.  A substantial part of the skull, vertebrae, both humeri along with hind limb material and parts of the pelvis were recovered. The skull was prepared at the University of Alberta Laboratory for Vertebrate Palaeontology.

The skull of the holotype specimen (UALVP 52981). Picture credit: Khoi Nguyen.

Picture credit: Khoi Nguyen

A Tyrannosaur with Unique Anatomical Traits

The anatomy of Tromerosaurus proved particularly interesting. Tyrannosaurids are traditionally divided into two important branches: Albertosaurinae and Tyrannosaurinae. Albertosaurines include Albertosaurus and Gorgosaurus. Tyrannosaurines include apex predators such as Daspletosaurus, Tarbosaurus and Tyrannosaurus. However, Tromerosaurus does not fit comfortably into this simple division.

Its anatomy combines characteristics seen in Gorgosaurus with features associated with Daspletosaurus. The research team found particularly important differences in the maxilla, the large tooth-bearing bone forming much of the side of the upper jaw. In addition, morphometric analysis revealed an intermediate morphology. For example, Tromerosaurus has a proportionally longer maxillary fenestra and a narrower pila promaxillaris (the strut of bone that separates the promaxillary fenestra from the maxillary fenestra in the skull), than Gorgosaurus libratus.

This unusual mixture of anatomical features makes the new taxon important for understanding early tyrannosaurid evolution.  It also suggests a greater diversity of tyrannosaur species in North America during the Late Cretaceous than previously thought.

Tromerosaurus solumons humeri (upper arm bones). Picture credit: Mark Powers (University of Alberta).

Picture credit: Mark Powers (University of Alberta)

Fossils Previously Assigned to the Gorgosaurus Genus

The researchers did not restrict their study to the holotype specimen.  Instead, they conducted an extensive examination of other tyrannosaur fossils.  It was discovered that some specimens previously assigned to the Gorgosaurus genus could instead by referred to T. solumons. Among the reassigned fossils is the substantial specimen TMP 1994.012.0602 and another individual, TMP 1995.005.0001. Additional isolated maxillary material has also been referred to the new tyrannosaur taxon.

Consequently, palaeontologists have fossils representing animals of different sizes and growth stages. This provides considerably more anatomical information than would be available from the holotype alone.

Skeletal reconstruction of Tromerosaurus solumons (A), size estimates vary but when fully grown this dinosaur could have had a body length of between 7 and 9 metres. Referred specimens and the skeletal components (B). Picture credit: Figure 4 in Powers et al 2026..

Picture credit: Figure 4 in Powers et al 2026

Tromerosaurus, Gorgosaurus and the Fossil Record

The stratigraphic distribution of these fossils provides another important piece of evidence. Tromerosaurus and Gorgosaurus appear to have had a restricted period of stratigraphic overlap. This supports the researchers’ interpretation that they represent distinct taxa rather than merely different growth stages or successive forms of the same tyrannosaur lineage. This has wider implications. For example, large tyrannosaurids have sometimes been regarded as comparatively long-lived species with relatively low taxonomic diversity. In contrast, the herbivorous dinosaurs living alongside them appear extremely diverse.

For instance, researchers have identified numerous species of ceratopsian in North America.  Many of these species were coeval. High endemism within centrosaurines was demonstrated with the discovery of Lokiceratops (L. rangiformis) from the Judith River Formation of Montana.

To read more about the discovery of Lokiceratops: A New Horned Dinosaur from Montana.

A new lambeosaurine hadrosaur from the Oldman Formation: A Newly Described Lambeosaurine Dinosaur.

The discovery of Tromerosaurus adds evidence suggesting that tyrannosaur diversity may have been underestimated.

The pelvis of the holotype specimen (UALVP 52981). Picture credit: Mark Powers (University of Alberta).

Picture credit: Mark Powers (University of Alberta)

Finding a Place for Tromerosaurus in the Tyrannosaur Family Tree

Perhaps the most fascinating part of the study concerns the dinosaur’s evolutionary relationships. The researchers tested the phylogenetic position of Tromerosaurus using different analytical methods. Remarkably, they obtained different results. A parsimony analysis placed Tromerosaurus as the earliest-diverging member of the Albertosaurinae. However, a Bayesian analysis recovered it within the Tyrannosaurinae sub-family. This discrepancy is scientifically important.

Tromerosaurus possesses a mosaic of characteristics associated with both sub-families. Its anatomy could therefore record a period when the distinctive features of albertosaurines and tyrannosaurines were becoming established. The researchers propose that the divergence of these two major tyrannosaurid lineages could have occurred later than previously thought. Furthermore, anatomical characteristics may have been acquired remarkably rapidly as tyrannosaurids diversified during the Late Cretaceous.

What’s In a Name?

The etymology of this new taxon is fascinating. The genus name combines the Greek “tromeros”, meaning frightening, terrible or alarming, with “sauros”, meaning lizard. The choice also echoes the names Daspletosaurus (“frightful lizard”) and Gorgosaurus (“dreadful/terrible lizard”), reflecting the animal’s intriguing combination of Albertosaurinae and Tyrannosaurinae anatomical characteristics.

The species name combines the Latin terms for “lonely mountain”.  It relates to the isolated nature of the lacrimal horn associated with the skull.  There is also a deliberate literary connection. The name references the Lonely Mountain, home of the dragon Smaug in J. R. R. Tolkien’s famous book entitled “The Hobbit”.

Tromerosaurus solumons – Leads to a Re-examination of Tyrannosaur Evolution

The scientific description of Tromerosaurus solumons demonstrates how museum specimens can transform our understanding of theropod dinosaur evolution. Some fossils referred to the new taxon had previously been interpreted as belonging to other tyrannosaurids. Detailed anatomical comparisons and improved information about their geological positions allowed researchers to recognise a previously unknown predator. Furthermore, Tromerosaurus suggests tyrannosaur evolution was perhaps more dynamic than traditionally envisaged.

Rather than consisting of a few long-lived species gradually replacing one another, Late Cretaceous tyrannosaurids may have undergone periods of relatively rapid diversification. Their evolutionary history could have been every bit as complex as that of the horned dinosaurs and duck-billed dinosaurs upon which they preyed.

Mike from Everything Dinosaur commented:

“Tromerosaurus solumons is a fascinating addition to the Tyrannosauridae family. It demonstrates how difficult it can be to unravel the evolutionary relationships of these theropods. The mixture of anatomical characteristics associated with different tyrannosaurid lineages makes this new taxon particularly significant.  Moreover, the study also highlights the importance of revisiting previously collected fossils. Specimens originally assigned to familiar genera such as Gorgosaurus can provide fresh information when examined in the light of new discoveries.”

A new tyrannosaur from the Foremost Formation of Alberta: Canada’s Oldest Tyrannosaur.

Everything Dinosaur acknowledges the assistance of PhD student Mark Powers and the University of Alberta in the compilation of this article.

The scientific paper: “A new albertosaurine from the Oldman Formation, Alberta, Canada, illuminates ambiguity between albertosaurine and tyrannosaurine characteristics” by Mark J. Power, James G. Napoli, Colton C. Coppock, Henry S. Sharpe, Christiana W. Garros, Alexandre V. Demers-Potvin, Gorm S. Raun, Jordan C. Stock, Tetsuto Miyashita and Philip J. Currie published in the Journal of Vertebrate Paleontology.