Fossilized Stomach Contents of Armored Dinosaur Reveal Its Last Meal

Nom nom nom nom. Illustration of Borealopelta markmitchelli dinosaur.
Nom nom nom nom. Illustration of Borealopelta markmitchelli dinosaur.
Illustration: Julius Csotonyi

A 110-million-year-old fossil found nine years ago at an open pit mine in Alberta is providing fascinating new details about the dietary habits of plant-eating armored dinosaurs and the environments in which they lived.

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“This is one of the best-preserved dinosaurs in the world,” Caleb Brown, a paleontologist at Royal Tyrrell Museum, told Gizmodo back in 2017 when the exquisite fossil was first unveiled. Dating back to the Early Cretaceous, the nodosaur skeleton—a kind of ankylosaur—retained features rarely seen in an armored dinosaur fossil, including skin and scale preservation, intact horn sheaths, and its original shape.

At the time, Brown and his colleagues were hopeful that further analysis of the fossil might reveal even more details, such as the contents of its digestive system. And here we are, three years later, reporting on this very thing. The new study, describing the stomach contents of a fossilized Borealopelta markmitchelli specimen, was published today in Royal Society Open Science.

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The Borealopelta markmitchelli fossil.
The Borealopelta markmitchelli fossil.
Image: Royal Tyrrell Museum of Palaeontology

Jelle Wiersma, a geoscientist and Ph.D. candidate at James Cook University in Australia, said the study is offering new insights into dinosaur diets.

“This study is crucial because, in general, very little is known what exactly dinosaurs ate beyond the general scope of plants or meat,” Wiersma, who’s not affiliated with the new research, told Gizmodo. “What or whom dinosaurs ate is often an educated guess based on the fossil plants and animals that occur together in the same place and time and are preserved in the rock record. This type of evidence is indirect, and paleontologists can often only infer what was on the menu of dinosaurs based on such fossil associations.”

This fossil was found at an open pit mine north of Fort McMurray, Alberta, back in 2011. Its remarkable preservation was due to a series of fortunate events—fortunate, at least, for paleontologists. Shortly after foraging, the 2,900-pound (1,300-kilogram) behemoth died close to shore, and its body drifted out to sea. Eventually, the body settled to the seafloor where it became preserved in mud, a patch of Early Cretaceous real estate now known as the Clearwater Formation.

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Analysis of the nodosaur’s abdominal cavity, roughly the size of a basketball, yielded new insights into the dietary preferences of these creatures. To analyze the cololite—i.e., fossilized stomach contents—the researchers took several thin sections cut from the specimen, which were then observed under a microscope. In a press release, David Greenwood, a co-author of the new study and a biologist at Brandon University, said, “we were shocked to see beautifully preserved and concentrated plant material,” adding that marine rocks almost never provide “such superb preservation of leaves, including the microscopic, spore-producing sporangia of ferns.”

The cololite primarily consisted of chewed leaf material, but it also retained evidence of stems and twigs. Microfossils found within this abdominal mass were then compared to plants known to exist in this region 110 million years ago. In total, the researchers identified 48 distinct microfossils, including evidence of ferns, moss, conifers, and flowering plants. Interestingly, this animal was a choosy eater, ignoring specific types of ferns and conifers known to exist in its foraging grounds.

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Wiersma, who in 2018 analyzed a stunning skeleton belonging to a different kind of ankylosaur, Akainacephalus johnsoni, was particularly stoked about the new study owing to the rarity of these creatures in the fossil record.

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“We know that armored dinosaurs had small, leaf-shaped teeth, and historically it was assumed that because of those small teeth they were likely not capable of processing hard and fibrous plants and instead consumed mostly softer varieties,” he told Gizmodo. “Recent studies analyzed their teeth more closely and suggested that these animals could in fact eat tougher plant material than was previously assumed. The data from this study undeniably confirms this and visually shows that armored dinosaurs actually consumed quite a diverse variety of plants, including some tough ones.”

But that’s not all they found.

The researchers also documented the presence of gastroliths, known as gizzard stones. Some herbivores, both extinct and extant, like to swallow stones, which helps them digest food. Incredibly, the researchers also found traces of charcoal, namely burnt plant fragments. This particular Borealopelta specimen was likely foraging in an area recently scorched by wildfires and was munching on ferns, a plant that’s known to take advantage of burnt landscapes, according to the new research.

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“This adaptation to a fire ecology is new information,” explained Greenwood. “Like large herbivores alive today, such as moose and deer and elephants in Africa, these nodosaurs by their feeding would have shaped the vegetation on the landscape, possibly maintaining more open areas by their grazing.”

This creature appears to have died shortly after its last meal. What’s more, the condition of the consumed plants suggests the nodosaur died at some point between late spring and the middle of summer.

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“I think the authors do a very good job justifying why these plant fossils are actual stomach contents, as opposed to something that got washed in [after death],” said Randall Irmis, a paleontologist at the University of Utah, in an email to Gizmodo. “This new discovery provides much more detail about what ankylosaurians ate—the one other good example is Kunbarrasaurus from Australia, but much of the plant matter was unidentifiable, so it was hard to conclude exactly why type of plants it was eating.”

The new findings aren’t necessarily indicative of all armored dinosaurs or even of all members of the species. When looking at one fossil, it’s hard to know whether you’re seeing an outlier.

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“This study is based on a single fossil specimen, and as the authors point out, the food in its stomach was likely its final meal shortly before it died, so it really represents a very brief moment in time,” said Wiersma. “To better understand the long-term diet of Borealopelta on a species level or even for armored dinosaurs as a group, we would need a lot more data from many more fossil specimens with similar, or different, gut contents.”

Sadly, given how rarely paleontologists find these creatures, it might be a long time before we can gain that knowledge, he said.

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“But that is okay, because fossils really tell us a story that reflects a short moment in time, almost like a photograph in stone,” he added. “Nonetheless, this study provides new and important data that improves our understanding of dinosaur behavior, which is always very exciting for us paleontologists and the general public alike.”

Looking ahead, the researchers plan to study the fossil in hopes of detecting internal organs and gaining new insights into the composition of Early Cretaceous forests. Encouragingly, this incredible Borealopelta specimen still has stories to tell.

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Correction: A previous version of the comment from Randall Irmis omitted his reference to Kunbarrasaurus. His statement that “much of the plant matter was unidentifiable” referred to Kunbarrasaurus, not Borealopelta. We regret the error.

George is a senior staff reporter at Gizmodo.

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DISCUSSION

plectro1
Darwinian Man

The paper doesn’t appear to be posted at the Royal Society site yet.

Nice to see Caleb and Don Henderson getting notice again. Good guys, the both of them.

ETA something in EurekAlert, but I don’t think that it adds much to the above article. And links to the Royal Society site elsewhere also lead nowhere - the publication must still be under embargo, I should have been able to get at it through my university library.