A ‘hell chicken’ that lived beside T. rex had jaws made for mashing fruit

A small feathered dinosaur that lived alongside Tyrannosaurus rex had a jaw that slid back and forth like a parrot’s, and the team that described it argues it was built to mash fruit. The animal, named Infernogallus jamesi, or “hell chicken”, came from a lineage of meat-eaters, yet its skull carries the muscle layout seen today only in birds that live on soft fruit.

If the interpretation holds, it is the first dinosaur known to have specialized in fruit, and the first solid link between dinosaurs and the rise of flowering plants. Paleontologists have looked for that link for decades without finding direct anatomical evidence. A turkey-sized animal from the last days of the dinosaurs may supply it.

Infernogallus belongs to the caenagnathids, a group of toothless, beaked, feathered dinosaurs related to Oviraptor. Their remains are mostly isolated jaws and limb bones, because their light, air-filled skeletons rarely survived burial intact. “For more than 100 years, we didn’t know what the skulls of these animals looked like,” said Gregory Funston of Stony Brook University, who led the study. “Now, we know they were even weirder than we could have predicted.”

The new skull is nearly complete and still articulated, the first such skull for the whole group. It comes from the Hell Creek Formation, the rock layers of the northern Great Plains that also yield T. rex and Triceratops. The animal weighed about 12 kilograms and, according to growth rings in its bones, was at least six years old and fully grown, which makes it one of the smallest members of its family.

How CT scans rebuilt the jaw muscles

The team scanned the skull with micro-computed tomography, a high-resolution form of X-ray scanning, and separated every bone digitally. Because fossil skulls are often crushed, they also corrected the distortion to restore the skull’s original shape. Scars and textured patches on the bone mark where jaw muscles once attached, so the researchers could rebuild each jaw-closing muscle and calculate the direction in which it pulled.

The surprise sat in the roof of the mouth. In Infernogallus, the palate bones arch downward into the mouth itself, which turns some jaw muscles to face front-to-back instead of up-and-down. That arrangement would have let the lower jaw slide forward and backward against the upper one, by up to about 15 millimeters, rather than snapping shut in a single vertical bite as in T. rex.

The researchers then compared these muscle directions with those of living birds and of other dinosaurs. Among the birds, the closest match was Pesquet’s parrot (Psittrichas fulgidus), also called the vulturine parrot, a New Guinea species that lives mostly on soft fruit. The team’s other comparison was with the green sea turtle, whose horny jaws carry grinding ridges and a central groove for working soft plants. The lower jaws of caenagnathids have nearly the same pattern of ridges and grooves, which would have met the bony bulge of the palate as the jaw slid.

Why fruit and not leaves or meat

A grinding bite alone does not prove a fruit diet, so the authors stack several clues. The muscle layout points to a weak bite, poor for tough stems, seeds or prey. No caenagnathid or close relative has ever been found with gizzard stones, the swallowed pebbles that many plant-eating dinosaurs used to grind fibrous food. Caenagnathids also had short bodies with little room for a long gut, the opposite of what a leaf-eater needs to ferment tough plant matter.

Taken together, the evidence suggests food that was soft and easy to digest, but that still needed processing in the mouth. Fleshy fruit fits that description. “It’s pretty rare for animals to become specialized for a diet of fruit, so when it happens, it comes with some remarkable adaptations,” said Thomas Dudgeon, a postdoctoral fellow at the Royal Ontario Museum and a co-author. The team argues the skull was suited to stripping the flesh off stone fruits and discarding the seed.

Caenagnathids arose just after the first fleshy fruits

Flowering plants spread across the land during the Cretaceous and pushed aside the cone-bearing plants that had dominated before them. Fleshy fruits appeared in that period and grew larger and more varied over tens of millions of years. The team’s dated family tree places the origin of caenagnathids between about 120 and 108 million years ago, shortly after the first fleshy fruits. The deep-beaked branch to which Infernogallus belongs appeared roughly 80 million years ago, as fruits became bigger and more common.

That timing matters because earlier studies found no clear match between the rise of dinosaur plant-eaters and the spread of flowering plants. If caenagnathids ate fruit, they may also have spread seeds, a job that birds, reptiles and small mammals do today. The group also includes far bigger animals: its Hell Creek relative Anzu wyliei, nicknamed the “chicken from hell” when it was described, weighed hundreds of kilograms, and the Asian Gigantoraptor more than 1,800 kilograms.

“Complete remains of small dinosaurs like Infernogallus are very rare in the fossil record,” said David Evans, chief curator of natural history at the Royal Ontario Museum and senior author of the study. “This discovery shows that we still have a lot to learn about the world of T. rex, and about dinosaurs more generally.”

What the skull cannot prove

No one has found fruit, seeds or stomach contents with Infernogallus. The diet is an inference from jaw anatomy, and the authors themselves describe caenagnathids as one of the strongest candidates for a flowering-plant diet in dinosaurs, not as proof. Their abstract says the group’s role in the spread of fruit “remains unclear”.

The statistics are weaker than the anatomy. One peer reviewer wrote that the first version’s ecological conclusions “largely are qualitative in nature” and were not supported by statistical tests. The team added three discriminant analyses, which sort animals into diet groups from their measurements, but the sample held only ten living birds with known diets. The first method misclassified three of those ten birds and labeled almost every dinosaur, T. rex included, an omnivore with more than 95 percent certainty. Infernogallus was the only exception, at 94.3 percent. A simpler version gave it 25 percent odds of a soft-plant diet, while every other dinosaur came out more than 85 percent likely to be an omnivore. The authors call these tests “inadequate to fully address the question” and rest their case on the anatomy.

Another reviewer pointed out that the 15-millimeter jaw slide is a maximum set by bone, and that cartilage and muscle probably limited the real movement. The authors also caution that their conclusion does not extend to all relatives: Oviraptor’s closer kin, the oviraptorids, had stronger, parrot-like skulls that look better suited to nuts and seeds.

Common questions about Infernogallus

Did any dinosaurs eat fruit?

Plant-eating dinosaurs may well have eaten fruit now and then, but Infernogallus is the first with a skull that appears specialized for it. Its jaw muscles and sliding jaw joint match those of fruit-eating parrots, which suggests fruit was a main food rather than an occasional one.

What does Infernogallus mean?

The name means “hell chicken”. It refers to the Hell Creek Formation, where the fossils were found, and to the animal’s bird-like, turkey-sized build.

How big was Infernogallus?

It weighed an estimated 12 kilograms, about the size of a large turkey. Bone growth rings show the holotype was an adult at least six years old, so it was a small species, not a juvenile.

Did Infernogallus live at the same time as T. rex?

Yes. It comes from the Hell Creek Formation, which dates to the final two million years or so before the asteroid impact 66 million years ago, the same rocks that yield T. rex and Triceratops.

A museum skull and an open question

The skull and partial skeleton, collected in 2011, are on display at the Royal Ontario Museum in Toronto. Additional jaw and palate bones from Montana, North Dakota and South Dakota were assigned to the species. The paper appeared online in Nature Communications on 10 October 2026, and the Royal Ontario Museum and Stony Brook University announced the discovery on 27 and 28 October.

The authors propose further tests, such as studying the feather pigments that many living birds obtain from fruit. The larger question stays open: whether these small fruit-eaters helped spread the flowering plants that shaped the forests growing back after the asteroid.

Reference: Funston et al., “Fruit-eating adaptations in a Late Cretaceous oviraptorosaur (Theropoda),” Nature Communications, 2026. DOI: 10.1038/s41467-026-78343-w

Tags: dinosaurs, paleontology, Tyrannosaurus rex, flowering plants, Hell Creek Formation, Infernogallus