In the movie “Jurassic Park,” a character proclaims there is nothing to fear from a towering Brachiosaurus, because it’s a “veggie-saurus” that eats only plants. Littlefoot, the “Longneck” dinosaur in the “Land Before Time” series, chows down on leaves, or “tree stars.” But while pop culture and general scientific opinion have agreed for decades that the long-necked sauropod dinosaurs were herbivores, there was no definitive proof found in the fossil record.
But there were hints of a diet full of green stuff.
Fossils of sauropods, which stomped across the planet for 130 million years, are plentiful; additionally, herbivores tend to outnumber those of carnivores. The animals had small, peg-like teeth, and their huge, lumbering bodies seemed ill-equipped to chase down prey. “Plants were pretty much the only option,” said Stephen Poropat, a paleontologist and the deputy director of the Western Australian Organic and Isotope Geochemistry Center at Curtin University in Perth.
A study published Monday in the journal Current Biology provides what may be the first concrete proof to support this argument, in the form of fossilized plants discovered in the belly of a sauropod. “It’s the smoking gun, or the steaming guts, as it were — the actual direct evidence in the belly of the beast,” Dr. Poropat said. “It’s never been found before for a sauropod dinosaur.”
Dr. Poropat, along with scientists and volunteers from the Australian Age of Dinosaurs Museum in Corfield, encountered the fossil, which is at the heart of their new paper, on a dig in the Winton Formation in Queensland, Australia, in 2017. The team was excavating a 36-foot-long juvenile Diamantinasaurus matildae, nicknamed Judy after the museum’s co-founder Judy Elliott, when the scientists spotted something strange: a layer of fossilized plant material near the sauropod’s pelvis.
“We knew we’d found something exceptional,” Dr. Poropat said, but he was hesitant to jump to conclusions. Fossilized gut contents, called cololites, are rare, especially from plant-eating dinosaurs, whose leafy diets don’t preserve as well as the bones preserved in the bellies of carnivores.
The researchers needed to rule out the possibility that the plants had simply been washed into Judy’s gut and had fossilized alongside the dinosaur. “One of the things that sealed the deal for me was the fact that we found so few plants anywhere else in the site,” Dr. Poropat said. Some of the leaves were preserved right alongside a layer of fossilized skin, another clue that the plants really did belong with the skeleton. “That was the clincher,” he added.
The research team analyzed the masses of fossilized plants for biomarkers, which are “essentially, molecular fossils,” Dr. Poropat said. These traces of ancient compounds indicated that the plants in Judy’s gut belonged to several botanical families, including foliage from tall conifer trees and relatively recently-evolved flowering plants that would have grown closer to the ground.
Judy’s cololites reveal not only what long-necked dinosaurs ate, but how they ate. The nearly-pristine leaves show that “sauropods didn’t chew at all,” Dr. Poropat said. “They snipped their food, swallowed and then let their gut bacteria do the rest of the work for up to two weeks before excreting what’s left of the meal.”
The vegetarian content of the cololites dovetailed with a longstanding hypothesis that sauropods relied on a varied diet, consumed as efficiently as possible, in order to get so huge. “If you’re small, you can be picky,” said P. Martin Sander, a professor of paleontology at the University of Bonn in Germany who was not involved with the study. “If you’re very large, you cannot be specific in your feeding, you have to just wolf it down.”
Judy is just one specimen among countless long-necked dinosaurs, so it’s not clear how well this fossil represents the feeding behavior of sauropod dinosaurs as a whole. But to Dr. Sander, even a single sauropod cololite is worth celebrating. “The amazing thing for me is that it actually preserved,” Dr. Sander said. “I didn’t dare hope that it would actually come along.”
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