Sauropods, the largest terrestrial animals ever to have lived, may have relied on foods more nutritious than ferns and conifers to grow to massive size.

MARK WITTON

Sauropods grew big by munching ‘superfoods’ with sturdy beaks

BRISBANE, AUSTRALIA—How did sauropod dinosaurs, the biggest creatures ever to have thundered across Earth, bulk up to the weight of more than 10 African bull elephants on a spartan diet of prehistoric greens? Many herbivores today grow fat on energy-rich grasses, but these and other nutritious flowering plants didn't become common until near the end of the dinosaurs' reign. Now, researchers think they have glimpsed the answer: a surprisingly nutrient-rich plant that could have been a mainstay of these dinosaurs' diets, and turtlelike beaks that buttressed sauropods' peglike teeth as they relentlessly stripped foliage from plants.

"We are seeing that they were able to acquire large volumes of food rapidly, and possibly nutrient-rich food," says Stephen Poropat, a paleontologist at Swinburne University in Melbourne, Australia.

Researchers at the University of Bonn in Germany presented the findings last week at the annual meeting of the Society of Vertebrate Paleontology here. Their previous work helped show that sauropods were eating machines that gulped down vegetation without chewing. They swung their long necks over vast areas, like prehistoric lawn mowers, while saving energy by keeping their bodies in one spot. The new studies add detail by exploring the beasts' diet and jaw structure.

One study, by Bonn's Carole Gee and her colleagues, identified what may have been the superfood of the dinosaur era. Her team zeroed in on the nutritional content of low-growing, spore-bearing horsetails, or Equisetum, which were widespread during the Jurassic period and still grow today.

Horsetails appeared to be poor fodder in previous tests, which simply burned the plants to measure carbon content, Gee says. Instead, her team adapted the Hohenheim gas test, a method for assessing the quality of fodder for farm animals. They fermented modern horsetails for 3 days to simulate the journey through a sauropod's gut and measured the volume of gas produced—an indicator of energy content. The researchers were astounded to find that horsetails released more energy than any other plant group, including 16 modern grasses. Equisetum is rich in protein, they say, and far more nutritious than the ferns, cycads, and conifers common in the dinosaur era. Gee argues that horsetails by rivers and lakes would have offered sauropods, especially young ones, "a plentiful, accessible, and extremely nutritious food."

Even eating superfoods, sauropods must have vacuumed up as much as 1 ton or more of plant matter per day. To understand the mechanics, another Bonn team analyzed the beasts' jaws.

For decades, paleontologists have dug up puzzling fossils: rows of isolated sauropod teeth, still neatly arranged as they would have been in the mouth, with not a scrap of bone encasing them. "There must have been something holding them in place," Bonn's Kayleigh Wiersma says. "Otherwise they would have been scattered all around the dig site."

In some skulls that retain teeth, they seem to be almost falling out of the sockets. "You can't have teeth exposed to that degree," says Steve Salisbury, a paleontologist at the University of Queensland here. "It seems likely there would have been some tissue that enclosed the base at least."

Wiersma and research leader Martin Sander studied seven sets of tooth rows, with up to 40 teeth each, from sauropods including Diplodocus, Brachiosaurus, and Apatosaurus. Wiersma said at the meeting that paleontologists may have had the faces of these iconic dinosaurs all wrong: Instead of the lizardlike lips shown in artists' concepts, the behemoths likely sported beaks as well as teeth, unlike any living animal.

The researchers found that sauropod teeth typically show surface wear only about halfway down to the jaw. That suggests the teeth were once deeply embedded in a supporting structure. The researchers also found tiny pits in the surface of the jaw, perhaps indicating blood vessels to nourish beaks. Similar pits and foramina are seen in other dinosaur bones near inferred structures, like the sheaths covering horns, thought to have been made of keratin, which forms our nails and birds' beaks and feathers.

Poropat cautions that expanded gum tissue, rather than a beak, might have held the teeth in place. But bony scaffolding that supported beaks is obvious in other dinosaurs, including Triceratops, Stegosaurus, and duck-billed hadrosaurs. Nevertheless, "I don't think we would have expected sauropods to have beaks," says Darren Naish, a paleontologist at the University of Southampton in the United Kingdom. It's a "whole new look."