Theropod dinosaur trackways can be used as indirect evidence of pre-avian aerial behavior, according to new research.
The animal responsible for Dromaeosauriformipes rarus tracks is believed to be a small microraptorine dinosaur related to the ancestors of birds. Image credit: Julius Csotonyi.
In the study, University of Maryland paleontologist Thomas Holtz Jr. and his colleagues examined two-toed footprints produced by a small, bird-like microraptorine dinosaur moving at high speed.
Scientifically named Dromaeosauriformipes rarus, these footprints are nearly 100 million years old (Cretaceous period) and were found preserved in a slab of rock in South Korea.
“This guy is dinky — one of the smallest dinosaurs that we have fossils of,” Dr. Holtz said.
“These tracks were a puzzle because their footprints are so tiny but they’re so far apart.”
The paleontologists found that the producer of Dromaeosauriformipes rarus didn’t merely run on land.
The animal flapped its feathered arms to achieve lift, which allowed it to travel faster than if it had relied solely on the strength of its legs.
Known as flap running, this form of movement falls somewhere between running and flying.
It generates enough aerodynamic force to lift an animal off the ground in bursts — enabling them to run up a tree, for example — but falls short of full-powered flight.
Though microraptorines are the cousins of Velociraptor and modern birds, it’s unknown whether Dromaeosauriformipes rarus could fly for longer periods of time.
A microraptorine theropod trackway from the Jinju Formation of South Korea. Image credit: Dececchi et al., doi: 10.1073/pnas.2413810121.
“We can now move past debate about whether pre-avian dinosaurs used their arms to help them move before flight evolved, and start to uncover missing details like which species had these abilities and when and to what extent they were developed,” said Dr. Michael Pittman, a paleontologist at the Chinese University of Hong Kong.
“Our findings suggest that Dromaeosauriformipes rarus would have needed to run at about 10.5 m per second (23.5 mph) to create the trackway using solely hindlimb power,” said Dakota State University paleontologist Dr. Alex Dececchi.
“The relative speed shown by our tracks is higher than any living running animal, including ostriches and cheetahs.”
“Because this also seemed highly improbable, we propose that the trackway was produced at lower speeds, with the dinosaur elongating its stride length using the aerodynamic force generated by flapping its feathered arms.”
“The footprints also suggest that the raptor was in the midst of taking off or landing,” Dr. Holtz said.
“It’s kind of like when a plane is coming down and bounces a little bit on the runway before slowing down.”
“The microraptorines that were capable of powered flight were still nowhere near as sophisticated — in terms of their flight apparatus — as a modern bird. They would have been relatively clumsy.”
The results were published in the Proceedings of the National Academy of Sciences.
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T. Alexander Dececchi et al. 2024. Theropod trackways as indirect evidence of pre-avian aerial behavior. PNAS 121 (44): e2413810121; doi: 10.1073/pnas.2413810121