Scientists have successfully unlocked the last meal of a large, armor-plated dinosaur and in doing so have brought “the beast back to life,” painting a picture of how the animal interacted with its environment at the end of its life in a way that skeletal fossilized remains have yet been able to do.

The 1,300-kilogram (2,866-pound) nodosaur (a type of ankylosaur) Borealopelta markmitchelli – which means “northern shield” – ate its last meal, died, and was then washed out to sea in what is now northern Alberta where it was entombed until its discovery in a 2011 mining operation. Notably, the thorny-backed animal’s stomach was especially well-preserved with a soccer ball-sized mass of digestive remains.

Palaeontologists have speculated what dinosaurs ate and have largely determined food preferences by applying characteristics of animals today, such as flattened molars indicative of a vegetable-based diet. Previous studies have found evidence of seeds and twigs in the guts of dinosaurs but had not determined the specific kinds of plants that were eaten.  

"The finding of the actual preserved stomach contents from a dinosaur is extraordinarily rare, and this stomach recovered from the mummified nodosaur by the museum team is by far the best-preserved dinosaur stomach ever found to date," said USask geologist and study author Jim Basinger in a statement.

Researchers at the Royal Tyrrell Museum of Palaeontology in Drumheller, Alta., Brandon University, and the University of Saskatchewan (USask) examined thin sections of the dinosaur's stomach contents under a microscope. They found that its last meal was one of large fern leaves containing 88 percent of chewed leaf material and 7 percent of stems and twigs.

The team says it was “shocked” to see the “beautifully preserved and concentrated plant material.” Before now, it was not conclusively known what herbivorous dinosaurs ate. Stomach contents were also compared with food plants that the fossil record suggests were available around the same time in the region. It appears that the dinosaur was a finicky eater with a preference for particularly large ferns known as leptosporangiate, the largest group of ferns today, and did not eat cycad or conifer leaves that were common at the time.

Also found within its stomach were 48 microfossils known as palynomorphs that are typical of pollen and spores from moss or liverwort, as well as 26 clubmosses and ferns, 13 conifers (gymnosperms) and two flowering plants (angiosperms). Interestingly, a considerable amount of charcoal from burnt plant fragments was also observed in the stomach, which suggests the animal was browsing in an area that had recently been burned and may have been taking advantage of fern growth that occurs following a fire.

"This adaptation to a fire ecology is new information. 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,” said Brandon University biologist David Greenwood.

Gastroliths, or gizzard stones, typically eaten by herbivorous animals like birds of today to help with digestion were also found within the dinosaur gut.

"We also know that based on how well-preserved both the plant fragments and animal itself are, the animal's death and burial must have followed shortly after the last meal," said Caleb Brown, Royal Tyrrell Museum palaeontologist and study leader. "Plants give us a much better idea of season than animals, and they indicate that the last meal and the animal's death and burial all happened in the late spring to mid-summer."

The scientists conclude that their findings change what is known about the diet of large herbivorous dinosaurs and help to illuminate how the animal interacted with its landscape, which plants it chose to eat, and where.  

"When people see this stunning fossil and are told that we know what its last meal was because its stomach was so well preserved inside the skeleton, it will almost bring the beast back to life for them, providing a glimpse of how the animal actually carried out its daily activities, where it lived, and what its preferred food was,” said Basinger.