Strange beaked 'hell chicken' is the first fruit-eating dinosaur

It is known from fossils unearthed in Montana and North Dakota.

The name Infernogallus means "hell chicken," a nod to its bird-like appearance and the fact that its fossils were found in the Hell Creek rock formation, which spans the US states of Montana, North Dakota, South Dakota and ​Wyoming and has yielded the remains of some of the most famous dinosaurs.

It would have eaten fruit and other soft plants in the subtropical coastal floodplain ecosystem it ​shared with the likes of apex predator. Tyrannosaurus, three-horned herbivore Triceratops and tank-like armored plant-eater Ankylosaurus. Infernogallus was about 5 feet (1.5 meters) long and weighed around ⁠25 pounds (11.3 kg).

While the fossils — one nearly complete skeleton and isolated bones from a jaw and palate — did not reveal feathers, the researchers believe Infernogallus was covered in them, based on ​fossils of close relatives.

It belonged to a group called theropods that includes T. rex and all the meat-eating dinosaurs, as well as some that took to eating plants and the entire bird ​lineage.

"This definitely expands the range of lifestyles we thought dinosaurs had, and it shows how adaptable theropods were," said paleontologist Greg Funston of Stony Brook University in New York, lead author of the research published in the journal. Nature Communications.

Fruits are the reproductive structures of angiosperms, also called flowering plants. Angiosperms first appeared earlier in the Cretaceous, around 130 to 140 million years ago, and subsequently took over landscapes previously dominated by plants called gymnosperms ​like conifers and ginkgoes.

Infernogallus shows that some dinosaurs may have had a close ecological relationship with flowering plants. "It has been proposed before that some groups of dinosaurs ate fruits, but there was ​never evidence to back it up," said study co-author Thomas Dudgeon, a postdoctoral researcher at the Royal Ontario Museum in Toronto.

"The discovery of Infernogallus shows that dinosaur diets were likely far more diverse than we ‌previously thought. Prior ⁠to this discovery, there was a bit of a mystery in dinosaur evolution. The evolution of flowering plants introduced a brand-new food source that undoubtedly had consequences for the animals living alongside them," Dudgeon said.

The fruit available for Infernogallus may have included various berries as well as drupes, a broad category that today includes types with a central pit like peaches and cherries as well as others like mangoes and olives. Three key features.

Infernogallus showed a range of features indicating a frugivorous diet. The three most important, Funston said, were the organization of jaw muscles that powered back-and-forth chewing ​motions, a mobile joint that enabled the jaw ​to slide forward, and a series of ⁠ridges and grooves on the beak to help mash and shear soft plants like fruits.

"We see these features separately in birds and turtles today that eat soft foods, like the fig-eating vulturine parrot or green sea turtles that chew soft sea grass. But no living animal has all ​three adaptations, showing just how specialized Infernogallus was," Funston said.

Infernogallus also shows how adaptable beaks are compared to teeth. "Once you've lost your teeth ​and developed a beak ⁠instead, the range of foods available dramatically increases, including plants, as long as you have some way to digest them," Funston said.

Most herbivorous theropods used stomach stones called gastroliths to grind food. But Infernogallus and other members of a lineage called caenagnathids chewed their food instead. Fruit-eating animals play an important role for angiosperms by dispersing seeds.

"Mammals and birds would probably also have eaten fruit, but they didn't show the ⁠same kinds ​of specializations for a frugivorous diet that Infernogallus does, so it might have been a less important resource for ​them.

Mammals and birds also were quite small in the Cretaceous, so it's unlikely that they were spreading very large seeds, or that they were spreading them big distances," Funston said.

"We know that these big-seeded fruits were proliferating and spreading, ​and it seems like caenagnathids could have fit this role — although we feel more evidence is needed before drawing that link confidently," Funston said.