A recent study reveals that newly identified birds from the Late Cretaceous period in North America were similar in size to hawks and possessed strong, raptor-like feet. This research, led by Alexander Clark from the University of Chicago, was published on October 9, 2024, in the open-access journal PLOS ONE.
During the Cretaceous period, the most varied birds belonged to a now-extinct group known as enantiornithines, which existed worldwide. However, the fossil record primarily reflects findings from the Lower Cretaceous, leaving a significant gap in the knowledge of avian evolution during the Late Cretaceous. This gap makes it challenging to fully understand the evolutionary trends of birds leading up to the end of the Mesozoic Era.
In this research, Clark and his team introduce three new enantiornithine species discovered among fossils in Montana’s Hell Creek Formation, which dates back to the late Cretaceous period (68-66 million years ago)—just before the mass extinction event that eliminated non-avian dinosaurs and enantiornithines. The fossils include lower leg bones from all three birds. Two of these are new species, named Magnusavis ekalakaensis and Avisaurus darwini, while the third species remains unnamed and is classified as Avisaurus.
These newly discovered birds are larger than their counterparts from the Early Cretaceous, with Avisaurus darwini estimated to weigh over one kilogram, comparable to a large hawk. Analyses of the leg bones reveal proportions and adaptations reminiscent of hawks and owls, suggesting they had powerful leg muscles and feet capable of gripping and possibly carrying sizeable prey, akin to some modern predatory birds.
These findings enhance the understanding of bird diversity during the Late Cretaceous, indicate a trend toward larger body sizes, and showcase the increased variety of ecological roles that enantiornithines developed over time. This study underscores the significance of even fragmentary fossils in uncovering vital ecological insights and clarifying evolutionary pathways.
The authors note: “Avisaurids, a subgroup of enantiornithine birds from the latest Cretaceous, exhibit hindlimb traits that show strong ankle flexibility, suggesting they could carry heavy prey and display behaviors similar to those of present-day raptors.”
