Exquisitely Preserved 'Mona Lisa' of Dinosaur Fossils Reveals Prehistoric Creature's Last Meal

In 2011, a worker operating heavy equipment at the Millennium oil sands mine in northern Alberta, Canada, uncovered the remains of an armored dinosaur so well preserved it looks less like a fossil and more like a living animal that somehow had the misfortune of being instantly turned to stone.

The extraordinary fossil has already provided scientists with a fresh understanding of how the interlocking spiked plates covering the animal’s tough hide functioned and fit together, reports Michael Greshko of National Geographic.

But now the dinosaur’s life-like remains are delivering even more intimate details about the 110-million-year-old herbivore: new research teases apart the fossilized contents of the dinosaur’s gut, revealing which plants it ate and even the season of its death, according to National Geographic.

Not long after what would be this nodosaur's (Borealopelta markmitchelli) final meal it died and was swept out to sea where it was almost perfectly preserved for 110 million years.

(Royal Tyrrell Museum of Palaeontology, Drumheller, Canada)

The armored dinosaur in question is Borealopelta markmitchelli, a burly, low-to-the-ground type of plant-eater called a nodosaur that lived in the Early Cretaceous. The nodosaur likely weighed around 3,000 pounds and was almost 20 feet long, per Greshko’s coverage for National Geographic in 2017 when the fossil first went on display at the Royal Tyrrell Museum of Paleontology in Canada.

After munching on what turned out to be its final meal, Borealopelta died, probably in a riverbed, and was washed out to sea where it sank straight to the bottom, landing on its back, according to a statement from the Royal Tyrrell Museum of Paleontology. The fine sediments of the seafloor mummified the dinosaur, eventually freezing its body in stone with such fidelity researchers say it looks like it’s merely sleeping.

It took fossil preparator Mark Mitchell, whose contribution is recognized in the latter half of the dino’s scientific name, more than 7,000 hours to chip and scratch away until Borealopelta’s shape emerged. The new analysis focused on a soccer-ball-sized mass found in the fossil’s abdominal cavity that paleontologists identified as being the contents of the creature’s digestive tract.

A section of the nodosaur's fossilized stomach contents.

(© Royal Tyrrell Museum of Palaeontology)

To pick apart the contents of this ball of partially digested fossilized plants, called a cololite, researchers sliced sheets of the specimen for examination under a microscope, reports George Dvorsky of Gizmodo.

The detail contained in these slices of ancient life astounded the authors of the study, published this week in the journal Royal Society Open Science.

"The leaf fragments and other plant fossils were preserved down to the cells," David Greenwood, a biologist at Brandon University and study coauthor, tells Ashley Strickland of CNN.

"We could see the different layers of cells in a leaf fragment including the epidermis with the pores, called stomata, through which plants take in carbon dioxide," Greenwood adds. "We could also see the surface patterning of the epidermis cells, which was like a jigsaw pattern that we see on many living ferns."

One of the super-thin slices of the nodosaur's stomach contents that researchers studied under a microscope.

(© Royal Tyrrell Museum of Palaeontology)

The researchers identified a group of gizzard stones, which the extinct animals swallowed to help pulverize their food similar to some modern birds, as well as a total of 48 microfossils of chewed-up leaves, stems and twigs, according to the paper. The team then compared the assortment to other fossil plants known to have existed in the region around the same time, per Gizmodo.

The cololite was mostly made up of ferns as well as mosses, conifers and a couple of flowering plants, the researchers write. But the paleontologists also noted the absence of certain plants.

"The lack of horsetails, and rarity of cycads and conifers is surprising, given that these are very common in the surrounding flora," Caleb Marshall Brown, the curator of dinosaur systematics and evolution at the Royal Tyrrell Museum of Paleontology and study co-author, tells CNN. "Even within ferns, it looks like Borealopelta may have had a preference for certain types of ferns, while ignoring others."

Using some paleontological sleuthing, the researchers also worked out the time of year the dinosaur died. Incomplete growth rings on the woody twigs found in the dinosaur’s gut signaled that the plants were about halfway through their growing season—which would have lasted from late spring to the dog days of summer—when they got chomped, according to National Geographic. The fern fronds also featured mature structures called sporangia which the plants use to disperse their spores. This herbaceous evidence slotted Borealopelta’s death sometime in early to mid-summer and suggested it died shortly after its last mouthful of greenery, per a statement from the University of Saskatchewan.

But the dino’s last meal had one more surprise for researchers: charcoal. Roughly six percent of the cololite was burnt up plant matter, suggesting to the researchers that Borealopelta was foraging among the new growth of a forest that had recently gone up in flames.

“This adaptation to a fire ecology is new information,” says Greenwood in the statement. “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.” 

It is fitting that such a life-like fossil should offer such a detailed glimpse into its ancient environment. “We get used to seeing [dinosaurs] as dead things, not as living things,” James Basinger, a paleobotanist at the University of Saskatchewan and co-author of the research, tells National Geographic. “This is a really important way to remind people that we’re actually dealing with things that wandered around the landscape and ate stuff ... not just bones in a museum.”

Further study of the unique specimen could help researchers understand how such a large animal survived on food with relatively low nutrient content, Brown tells CNN. The team also plans to search for traces of the dinosaur’s other internal organs, per Gizmodo, and to use their new knowledge of its diet to get a clearer picture of its habitat in the Early Cretaceous.

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