Description and Classification

Chirostenotes was a lightly built, bird-like dinosaur. It is estimated to have been about 2 to 2.5 meters (roughly 6.5 to 8 feet) long and may have weighed around 50 kilograms (110 pounds). It had long, slender legs, suggesting it was a fast runner. Like other oviraptorosaurs, Chirostenotes had a long neck, a short tail that likely ended in a fan of feathers, and a toothless beak. Its most distinctive feature, the hands, had three long, slender fingers with sharp claws. Scientists believe Chirostenotes was covered in feathers, similar to its relatives like Caudipteryx and Oviraptor.

Chirostenotes belongs to the group Oviraptorosauria, a diverse clade of feathered maniraptoran dinosaurs. Within this group, it is classified in the family Caenagnathidae. Caenagnathids, like Chirostenotes, are characterized by their toothless beaks, long limbs, and often elaborate crests (though a distinct crest for Chirostenotes is not definitively known). Other well-known caenagnathids include Anzu, sometimes nicknamed the “chicken from hell,” and Caenagnathus, with which Chirostenotes has a complex taxonomic relationship and is sometimes considered the same animal by different paleontologists.

Distinguishing Features

Chirostenotes had several features that helped scientists identify it and distinguish it from other dinosaurs:

• Elongated, slender hands with three fingers, the second finger being the longest.
• A toothless beak, which was probably covered in a horny sheath like that of a modern bird.
• Long, slender legs built for running.
• A relatively long neck compared to its body size.
• Like other oviraptorosaurs, it likely possessed a pygostyle (fused tail vertebrae), suggesting it had tail feathers.

Paleoenvironment and Diet

Chirostenotes lived in what is now Alberta, Canada, during the Campanian stage of the Late Cretaceous. Its fossils are commonly found in the Dinosaur Park Formation. This area was a warm, coastal lowland environment with numerous rivers, floodplains, swamps, and lush forests. Chirostenotes shared this habitat with a wide variety of other dinosaurs, including large herbivores like the duck-billed hadrosaurs (such as Parasaurolophus and Lambeosaurus), horned ceratopsians (like Centrosaurus and Styracosaurus), and armored ankylosaurs (such as Euoplocephalus). Predatory dinosaurs in this environment included tyrannosaurids like Gorgosaurus and Daspletosaurus.

The diet of Chirostenotes is thought to have been omnivorous. Its toothless beak could have been used to eat a variety of foods. Scientists suggest it might have eaten plants, seeds, fruits, eggs, insects, and small animals like lizards or mammals. Its agile build and nimble hands might have helped it catch small prey or manipulate food items. While no direct stomach contents have been found for Chirostenotes, its beak structure is similar to that of other oviraptorosaurs which are believed to have had a mixed diet.

Significance and Ongoing Research

Chirostenotes is significant because it is one of the best-known caenagnathid dinosaurs from North America. It helps scientists understand the diversity and geographical distribution of oviraptorosaurs, many of which, like Oviraptor philoceratops, are found in Asia. The discovery of Chirostenotes and its relatives shows that these bird-like dinosaurs were also thriving in North America.

Ongoing research continues to refine our understanding of Chirostenotes. One of the main areas of study is its complex taxonomic history. For a long time, parts like hands (Chirostenotes), jaws (Caenagnathus), and feet (Macrophalangia) were named as separate genera. Paleontologists are still working to determine if all these remains belong to a single species or represent closely related animals. Discoveries of more complete skeletons are crucial for resolving these questions. Further research also focuses on the exact diet and behavior of Chirostenotes and its role within the diverse ecosystems of Late Cretaceous North America, as well as its relationship to other caenagnathids like Elmisaurus and Anzu wyliei.