aucellum

*Auchellum* refers to a small, extinct genus of prehistoric birds that lived during the Late Cretaceous period, approximately 70–66 million years ago. Fossil remains of *Auchellum* have been discovered primarily in the western United States, particularly in the Hell Creek Formation of Montana and the Lance Formation of Wyoming and South Dakota. The genus is notable for its relatively well-preserved skeletal remains, including fragments of skulls, limb bones, and feathers, which provide insights into the morphology and possible behaviors of these birds.

The name *Auchellum* is derived from the Latinized form of the Auchela name, referencing the Auchela people, an Indigenous tribe historically associated with the region where the fossils were found. The type species, *Auchellum harrisi*, was first described in 2010 by paleontologists studying avian diversity in the Late Cretaceous. *Auchellum* is classified within the enantiornithine clade, a group of extinct birds that dominated terrestrial ecosystems before the extinction event that wiped out the non-avian dinosaurs.

Fossil evidence suggests that *Auchellum* was a small to medium-sized bird, likely weighing around 1–2 kilograms, with a body length of approximately 30–40 centimeters. Its skeletal structure indicates adaptations for arboreal (tree-dwelling) or semi-arboreal lifestyles, with strong limbs and possibly a grasping ability in its feet. The presence of feathers in some specimens further supports the idea that *Auchellum* was covered in plumage, similar to modern birds.

The discovery of *Auchellum* contributes to the understanding of avian evolution during the Late Cretaceous, particularly the diversity and ecological roles of enantiornithines. While these birds went extinct around the same time as many dinosaur groups, their fossils remain valuable for comparative studies with modern birds and other prehistoric avian lineages. Research on *Auchellum* continues to refine knowledge of bird anatomy, behavior, and the broader context of the Cretaceous-Tertiary transition.