The Fruit-Eating "Hell Chicken"

Research Background and the Discovery of the New Genus and Species "Infernogallus jamesi"

The Cretaceous period is known as an era when flowering and fruiting plants ("angiosperms") spread explosively, accompanied by a major diversification of herbivorous dinosaurs. Surprisingly, however, no conclusive evidence had ever been found showing that non-avian dinosaurs directly evolved anatomical structures to feed on the soft, fleshy fruits of angiosperms.

This major gap in paleontology has now been filled by a research team led by Dr. Gregory Funston of Stony Brook University, along with researchers from the Royal Ontario Museum (ROM) and the North Dakota Geological Survey (including Dr. Clint Boyd, Dr. Philip Currie, and Dr. David Evans). In a study published in the journal Nature Communications on October 10, 2026, the team formally described a new genus and species of caenagnathid oviraptorosaur (subfamily Caenagnathinae), "Infernogallus jamesi," based on five fossil specimens discovered in the Hell Creek Formation of North America, which dates to the very end of the Cretaceous (late Maastrichtian, approximately 68 to 66 million years ago).

The genus name "Infernogallus" combines the Latin words "Inferno" (hell) and "gallus" (chicken/rooster), meaning "Hell chicken"—a nod to both the Hell Creek Formation where the fossils were found and its turkey-sized, bird-like build. The specific name "jamesi" honors James William Boyd, the grandfather of co-author Dr. Clint Boyd, who inspired him to pursue a career in paleontology.

The First "Nearly Complete Skull" in Over a Century of Research

Caenagnathidae, the family to which Infernogallus belongs, is a group of theropods characterized by toothless, beak-like lower jaws, slender limbs, and bird-like bones lightened by air sacs (pneumatization). Because their bones are extremely thin and fragile, they usually shatter and scatter during fossilization. For over 100 years since research on this group began, not a single nearly complete, articulated skull—with bones still connected in their original positions—had ever been found.

However, the holotype specimen (ROM VP 65050), excavated in Garfield County, Montana, USA, in July 2011 and now housed and displayed at the Royal Ontario Museum, preserved the first "nearly complete articulated skull and lower jaw" in caenagnathid history. Furthermore, it was a miraculously preserved partial skeleton that included an articulated series of cervical and dorsal vertebrae, gastralia (belly ribs), the right shoulder girdle and forelimb, part of the pelvis, and part of the right hindlimb.

Not a Juvenile of a Large Species, but a "Small-Bodied Adult"

Measuring about 1.5 meters in total length with an estimated body mass of around 12 kilograms (range: 9–15 kg), Infernogallus is among the smallest members of Caenagnathidae. Because the same Hell Creek Formation was home to the giant caenagnathid Anzu wyliei (weighing around 300 kg) and the medium-sized Eoneophron infernalis (weighing around 80 kg), researchers needed to verify whether this small fossil was simply a juvenile of a larger species.

Unique Structure and Function of the Skull, Palate, and Lower Jaw

Because the discovered skull had been laterally compressed in the rock strata, the research team used high-resolution micro-CT scans to digitally segment each individual bone. Referencing 3D data from undeformed paratype specimens, they precisely retrodeformed the skull on a computer to restore its original three-dimensional shape. The results revealed a cranial architecture that overturns conventional wisdom about theropod skulls.

1. Enormous Eyes and an Extremely Reduced Temporal Fenestra

In side view, the most striking feature of the skull is that the circular orbit (eye socket) is enormous—occupying about 40% of the basal skull length—while the opening behind it, known as the "infratemporal fenestra," is drastically reduced.

In closely related Asian oviraptorids (such as Citipati), the infratemporal fenestra occupies 29% of the skull's length and 48% of its height, providing ample space around it for powerful jaw-closing muscles (the temporal adductor group). In Infernogallus, however, the infratemporal fenestra is shrunk to just 11% of the skull's length and 12.5% of its height, and the squamosal bone at the upper rear of the skull has completely lost the depressions and crests for muscle attachment. Instead, the jugal bone supporting the bottom of the eye expanded into a broad plate connecting directly to the squamosal behind it, while a large disc-like quadratojugal bone surrounded the ear opening (external acoustic meatus) in a unique reinforcing structure.

2. Enlargement of the Palate and Reinforcement of Pterygoideus Muscles

While the vertical jaw-closing muscles at the back of the skull were reduced, the bones and muscles of the roof of the mouth (the palate) were massively developed.

A structure formed by the maxilla and palate bones—the "maxillovomerine process"—projected prominently downward into the oral cavity, while the "pterygoid" bone behind it flared outward like a wide horizontal shelf. This pterygoid shelf featured deep depressions and a robust foundation to house the "pterygoideus muscle group," massive muscles responsible for pulling the lower jaw forward and backward.

3. Mortar-Like Beak, Powerful Tongue, and Sliding Jaw Joint

The toothless lower jaw, with its left and right halves completely fused together, forms an upturned beak at the tip reminiscent of a parrot or turtle. Its occlusal (biting) surface is lined with complex ridges and grooves, and when the mouth closed, the maxillovomerine process hanging from the palate fit snugly into a deep central trough in the lower jaw.

Additionally, the inner floor of the lower jaw bears a distinct W-shaped scar where the tongue-moving muscle (M. genioglossus) attached, indicating that Infernogallus possessed a thick, muscular tongue capable of deftly manipulating food inside the mouth. Furthermore, the jaw joint (the articulation between the quadrate and articular bones) consisted of a rounded, rail-like ridge fitting into a saddle-shaped groove, allowing the entire lower jaw to slide extensively fore and aft.

Muscle Reorganization and the "Fore-and-Aft Sliding" Chewing Mechanism

The research team reconstructed the jaw musculature onto the 3D skull model of Infernogallus and conducted statistical analyses comparing it with Tyrannosaurus, Allosaurus, Dromaeosaurus, therizinosaurs (Erlikosaurus), oviraptorids (Citipati), and modern birds.

The results revealed that whereas nearly all other theropods—including carnivorous dinosaurs and typical oviraptorids—specialized in generating strong vertical (orthal) jaw-closing forces, Infernogallus used its expanded pterygoideus muscles to maximize horizontal (fore-and-aft) jaw forces.

Striking Convergent Evolution with Modern "Fruit-Eating Parrots"

Comparing these changes in jaw musculature and mechanics with living birds revealed a striking case of convergent evolution. The evolutionary transition from the tall, box-like skull of oviraptorids to the low, elongated, fore-and-aft sliding skull of Infernogallus mirrors the exact evolutionary pathway seen in modern parrots—from generalist seed- and nut-cracking parrots (like African grey parrots) to the specialized fruit-eating "Pesquet's parrot (also known as the Dracula parrot, Psittrichas fulgidus)" of New Guinea.

Pesquet's parrot feeds almost exclusively on soft fruits such as figs. Rather than cracking hard seeds, it uses a feeding technique called "deflushing" to pulp the soft flesh in its mouth and strip it away from the hard seeds. Using a process of elimination, the research team also tested and ruled out other potential diets:

• Why It Was Not a Hard-Seed Cracker or Carnivore: Because its vertical bite force was very weak, its jaws were ill-suited for cracking hard nuts and seeds or shearing through meat and bone.
• Why Tough Leaves and Ferns Were Not Its Staple Diet: Digesting fibrous, tough foliage requires either teeth to finely shred plant matter, swallowed stones ("gastroliths") to grind food in a muscular gizzard, or a long digestive tract (a voluminous belly) to ferment plant fiber. However, Infernogallus completely lacked both teeth and gastroliths, and its torso was short and compact with no room for a long fermenting gut.

The only food source that satisfies all of these anatomical constraints—something soft enough to be crushed with weak bite forces, nutrient-rich and easily digestible without gastroliths or a long gut, yet requiring oral processing to strip flesh away from a hard pit before swallowing—is the angiosperm "drupe" (stone fruit), where soft flesh surrounds a hard pit much like modern peaches or cherries.

Coevolution with Angiosperm Fruit Diversification and the K-Pg Extinction Paradox

When the research team investigated the evolutionary history of Caenagnathidae using statistical models that estimate divergence times (Bayesian phylogenetic analysis), they found that the group's evolution closely matched the timeline of angiosperm fruit evolution.

Caenagnathidae is estimated to have originated during the Aptian to Albian stages of the Early Cretaceous (approximately 118 to 107 million years ago)—just 3 to 10 million years after the first fossil "drupes" (fleshy stone fruits) appeared on Earth. Indeed, examination of fossils of Microvenator celer, the most basal caenagnathid living in North America during that time, revealed that it already possessed early pterygoid features similar to those of Infernogallus.

Furthermore, from the late Santonian to early Campanian stages of the Late Cretaceous (around 85 to 80 million years ago), fruit diversity and fruit size increased significantly across the Northern Hemisphere (Laurasia). At this exact time, the subfamily "Caenagnathinae" (the group including Infernogallus and Anzu), equipped with complex occlusal ridges and advanced fore-and-aft jaw sliding, emerged and rapidly diversified. Because Infernogallus likely stripped the flesh from large-pitted fruits and spat out the pits, researchers infer that it acted as a "seed disperser" when eating small-seeded berries, while functioning as a pure "pulp consumer" when feeding on larger stone fruits.

Niche Partitioning Among Three Species in the Hell Creek Ecosystem

This discovery demonstrates that just before the asteroid impact, the North American Hell Creek Formation was home to at least three distinctly sized species of caenagnathids coexisting in the same environment: the small-bodied Infernogallus (approx. 12 kg), the medium-sized Eoneophron (approx. 80 kg), and the giant Anzu (approx. 300 kg). This "niche partitioning"—dividing up feeding heights and types of fruits or plants according to body size—strongly supports the view that dinosaurs maintained rich ecological diversity right up to their final moments.

Why Didn't It Survive? The Extinction Paradox of 66 Million Years Ago

The discovery of Infernogallus also casts new light on the criteria for survival during the asteroid impact 66 million years ago (the K-Pg boundary). Until now, the shared traits thought to have allowed modern birds to survive the mass extinction included "small body size," "high bird-like metabolism and growth rates," "a toothless beak," and "a non-carnivorous diet." Even though Infernogallus met every single one of these criteria, it still went extinct.

In other words, Dr. Funston and his colleagues conclude that the very "specialization for fruit-eating" that allowed caenagnathids to seize the opportunity of spreading angiosperms and flourish during the Late Cretaceous became an inescapable "evolutionary trap" when global catastrophe struck.

Critical Evaluation of the Frugivory Hypothesis and a Comprehensive Interpretation

While the announcement of a "fruit-eating dinosaur" by Dr. Funston's team generated widespread excitement, cautious counterarguments have also been raised from the perspectives of paleoecology, paleobotany, and paleoclimate. Paleontologist Dr. Nick Longrich of the University of Bath, UK, and others have raised four main questions regarding the idea that fruit was the primary staple of caenagnathids:

1. Body Size and Shared Jaw Anatomy Across Giant Species (Allometry): Most modern fruit-eating birds (such as toucans and Pesquet's parrot) and bats weigh less than 1 kilogram. At 12 kilograms, Infernogallus is already larger than nearly all of them, and it would be impossible to sustain giants with the exact same lower jaw structure—such as Anzu (approx. 300 kg) or Gigantoraptor (over 1.5 tons)—on small fruits alone. Critics point out that the reason relatives spanning a more than 100-fold difference in body mass all shared the same jaw design is more likely because it was adapted for general "herbivory (consuming leaves, stems, shoots, roots, etc.)," which works at any body size.
2. Terrestrial Build Unable to Climb Trees: Because most fruits grow high up in the tree canopy on slender branches, modern frugivores are almost exclusively flying birds and bats, or agile tree-climbing primates and marsupials (indeed, the Hell Creek Formation has yielded fossils of Glasbius, a small arboreal marsupial with teeth suited for fruit-eating). In contrast, with its short forelimbs and long cursorial hindlimbs built for running, Infernogallus was a strictly ground-dwelling dinosaur that could not climb out onto thin branches to harvest fruit.
3. Winter Cold and the Composition of Ancient Forests: The North American and Mongolian habitats where Infernogallus and its relatives lived were situated at relatively northern latitudes (around 41° to 52° N) at the time. Rather than tropical rainforests producing fruit year-round, these regions experienced temperate to subarctic climates with cold winters when plants went dormant. Moreover, the forests were dominated by conifers like Metasequoia and pines, or wind-dispersed relatives of plane trees (Platanaceae), making it unlikely that an animal could survive the winter relying solely on fruit.
4. Alternative Explanations for the Lack of Gastroliths: Ceratopsians (like Triceratops) and hadrosaurs (duck-billed dinosaurs) also ate tough plants without using gastroliths, because they thoroughly ground up plant matter inside their mouths. Similarly, the jaws of Infernogallus can be interpreted as having been used not just for fruit, but also—like tortoises and herbivorous waterfowl—to finely pulp and grind "soft aquatic plants, young leaves, shoots, and underground tubers (root vegetables)" right in the mouth.

Conclusion: The Theropod Jaw as a "Multi-Functional Food Processor"

Synthesizing both perspectives with the latest cranial analyses brings a more three-dimensional picture of Infernogallus into focus.

First and foremost, the skull of Infernogallus proves beyond doubt for the first time that non-avian theropods had moved beyond simple "gulping" or "up-and-down biting," evolving sophisticated "oral processing (chewing and pulping food inside the mouth)" rivaling that of mammals and specialized birds.

Considering the seasonal environment of the Late Cretaceous, it is most natural to view the jaw of Infernogallus not as an organ restricted to eating nothing but fruit 365 days a year, but rather as a "multi-functional food processor capable of pulping a variety of nutritious, soft plant tissues and fruits." From spring through autumn, when fruits were in season, Infernogallus undoubtedly sought out sweet, nutrient-rich angiosperm fruits (drupes and berries) as well as fleshy Ginkgo seeds, deftly using its sliding jaw and muscular tongue to strip and pulp the flesh. Then, during the fruitless winter months or in conifer-dominated forests, it likely used the very same grinding mechanism to mash soft young leaves, buds, aquatic plants, and underground tubers into a fine paste—overcoming its lack of gastroliths and a long gut to survive the winter.

It was precisely because of this versatile system for thorough oral grinding that Caenagnathidae was able to diversify into herbivorous and omnivorous dinosaurs of vastly different sizes—from the 12-kilogram Infernogallus to the 1.5-ton-plus Gigantoraptor—and continue thriving right up to the final moments of the Cretaceous period.

References & Citations

• Fruit-eating adaptations in a Late Cretaceous oviraptorosaur (Theropoda) - ResearchGate, https://www.researchgate.net/publication/415548160_Fruit-eating_adaptations_in_a_Late_Cretaceous_oviraptorosaur_Theropoda
• Meet The 'Hell Chicken', a Dinosaur With an Extremely Rare Type of Diet - ScienceAlert, https://www.sciencealert.com/meet-the-hell-chicken-a-dinosaur-with-an-extremely-rare-type-of-diet
• This Turkey-Sized "Hell Chicken" Lived Alongside T. rex and Ate Fruit - The Daily Galaxy, https://dailygalaxy.com/2026/11/hell-chicken-first-fruit-eating-dinosaur/
• Small, Chicken-Like Dinosaur May Have Had a Jaw Built for Fruit - Sci.News, https://www.sci.news/paleontology/infernogallus-jamesi-15128.html
• Rare fossil discovery reveals new dinosaur species that were specialized fruit-eaters - EurekAlert!, https://www.eurekalert.org/news-releases/1149430
• Meet the Hell Chicken: New Dinosaur Was Built to Eat Fruit - FossilGuy.com, https://www.fossilguy.com/news/hell-chicken-infernogallus-fruit-eating-dinosaur/index.htm
• Infernogallus jamesi Fossil on Display at Royal Ontario Museum - Everything Dinosaur, https://blog.everythingdinosaur.com/blog/_archives/2026/11/11/infernogallus-jamesi-fossil-on-display-at-royal-ontario-museum.html
• Were Caenagnathid Theropods Fruit-Eaters? Probably not. - Nick Longrich, https://www.nicklongrich.com/blog/were-caenagnathid-theropods-fruit-eaters-probably-not