Paleontologists have described three new enantiornithine birds from the Cretaceous Hell Creek Formation, two of which represent new avisaurid species. These birds lived alongside dinosaurs 68 million years ago and their powerful feet bones suggest they could have captured and carried off prey.
Reconstruction of an avisaurid (e.g., Avisaurus darwini). Image credit: Clark et al., doi: 10.1371/journal.pone.0310686.
The most diverse birds during the Cretaceous period were a now-extinct group called enantiornithines, known from all over the world during this time.
However, enantiornithines and other Mesozoic birds are mainly known from Lower Cretaceous deposits, with a relatively poor record from the Late Cretaceous.
Thus, there is a general lack of understanding of trends in bird evolution toward the end of the Mesozoic era.
The fossilized remains of the three new enantiornithine birds were found in the Hell Creek Formation of Montana, dating to the latest Cretaceous period.
Two are new species named Magnusavis ekalakaensis and Avisaurus darwini, while the third is an unnamed species of Avisaurus.
These birds are all larger than Early Cretaceous enantiornithines, with Avisaurus darwini estimated to have weighed over 1 kg, roughly the size of a large hawk.
“These discoveries have effectively doubled the number of bird species known from the Hell Creek Formation and will be critical for helping us to better understand why only some birds survived the mass extinction that wiped out T. rex and the avisaurids described here,” said Dr. Jingmai O’Connor, associate curator of fossil reptiles at Field Museum.
The team’s analysis of the leg bones of Avisaurus and its relatives revealed proportions and adaptations similar to hawks and owls, indicating powerful leg muscles and feet that could grip and potentially carry proportionally large prey, similar to some modern raptorial birds.
“Based on clues in their foot bones, we think these birds would have been able to catch and carry prey, similar to what a modern hawk or owl does,” said Alex Clark, a Ph.D. student at the Field Museum and the University of Chicago.
“While they might not be the first birds of prey to ever evolve, their fossils are the earliest known examples of predatory birds.”
The new species expand the known diversity of Late Cretaceous birds, confirm the trend toward large body size, and highlight how, over time, enantiornithines evolved a greater diversity of ecological roles.
“Avisaurids, a group of enantiornithine birds from the latest Cretaceous, exhibit hindlimb features indicating strong ankle flexion, which suggests the ability to carry heavy prey and behaviors similar to living raptorial birds,” the paleontologists said.
Their paper appears today in the journal PLoS ONE.
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A.D. Clark et al. 2024. New enantiornithine diversity in the Hell Creek Formation and the functional morphology of the avisaurid tarsometatarsus. PLoS ONE 19 (10): e0310686; doi: 10.1371/journal.pone.0310686
Source : Breaking Science News