Unenlagiidae

Lore & Background

The family Unenlagiidae traditionally includes the same members as the previously named subfamily of Dromaeosauridae, Unenlagiinae, so Unenlagiidae was often seen as a synonym of Dromaeosauridae. However, since the 2010s, subsequent studies have questioned this placement, necessitating the revival of the family name. Some have placed unenlagiids as outside Dromaeosauridae, being the sister taxon or closely related to Avialae, while others have placed the newly recognized halszkaraptorines in the family, as basal deinonychosaurs outside Dromaeosauridae and Troodontidae.

Reader's Guide

The significance of Unenlagiidae lies in its contested position within the evolutionary tree of paravian dinosaurs, highlighting the ongoing uncertainty in the relationships among dromaeosaurids, troodontids, and avialans. The inclusion of Halszkaraptorinae, whose members show adaptations for semiaquatic lifestyles, adds ecological diversity to the group. The 2021 naming of the clade Unenlagiinia for a unified Unenlagia+Halszkaraptor clade, recovered as basal dromaeosaurs, and the 2025 recovery of Unenlagiidae within Avialae, illustrate the fluidity of phylogenetic hypotheses. This family serves as a case study in how new fossil discoveries and analytical methods can reshape our understanding of dinosaur evolution, particularly the origins of birds.

Did You Know?

• Fossils of Unenlagiinae are found in Gondwanan deposits, while Halszkaraptorinae fossils are found in Laurasian deposits.
• Some members of Unenlagiidae were semiaquatic specialists.
• In 2025, Motta et al. recovered Unenlagiidae as within Avialae.