Did bird wings evolve from velociraptors? New study suggests yes

We all know that birds cannot fly without their wings; thanks to a wing structure called the propatagium, birds can sail in the air. Still, the evolutionary origin of this structure has long-baffled scientists.

Now, researchers from The University of Tokyo appear to have solved this mystery by demonstrating propatagium originated from dinosaurs, as per the release.

The early version of propatagium

It is known that certain lineages of the dinosaurs that lived millions of years ago gave rise to current birds. In order to explain some of the distinctive characteristics of birds, such as feathers and bone structure, experts have turned to dinosaurs.

Dinosaurs known as theropods, including Tyrannosaurus rex and Velociraptor, had arms rather than wings. It would be easier to understand how the contemporary bird branch of the tree of life evolved from arms to wings if researchers could locate evidence of an early version of the propatagium in these dinosaurs.

The propatagium comprises soft tissues that do not fossilize effectively, if at all. Therefore, it may not be able to find direct proof. Instead, scientists were forced to devise a ruse to ascertain whether or not a propatagium was present in a specimen.

“The solution we came up with to assess the presence of a propatagium was to collect data about the angles of joints along the arm, or wing, of a dinosaur or bird,” said Yurika Uno, a graduate student at Hirasawa's lab.

Researchers concluded that the famous Velociraptor belonged to a group of dinosaurs known as the maniraptoran theropods, where the propatagium most likely arose. This was backed up when the researchers identified the propatagium in preserved soft tissue fossils. This research means it’s now known when the propatagium came into being, leading researchers to the next question of how it came to be.

The team has already begun investigating possible links between the fossil findings and present vertebrate embryonic development.

“Dinosaurs portrayed in popular media are becoming more and more accurate,” said Hirasawa. “At least now we get to see features like feathers, but I hope we can see an even more up-to-date representation soon where theropods have their propatagium too.”

The study was published in Zoological Letters on February 23.

Study abstract:

Avian wings as organs for aerial locomotion are furnished with a highly specialized musculoskeletal system compared with the forelimbs of other tetrapod vertebrates. Among the specializations, the propatagium, which accompanies a skeletal muscle spanning between the shoulder and wrist on the leading edge of the wing, represents an evolutionary novelty established at a certain point in the lineage toward crown birds. However, because of the rarity of soft-tissue preservation in the fossil record, the evolutionary origin of the avian propatagium has remained elusive. Here we focus on articulated skeletons in the fossil record to show that angles of elbow joints in fossils are indicators of the propatagium in extant lineages of diapsids (crown birds and non-dinosaurian diapsids), and then use this relationship to narrow down the phylogenetic position acquiring the propatagium to the common ancestor of maniraptorans. Our analyses support the hypothesis that the preserved propatagium-like soft tissues in non-avian theropod dinosaurs (oviraptorosaurian Caudipteryx and dromaeosaurian Microraptor) are homologous with the avian propatagium, and indicate that all maniraptoran dinosaurs likely possessed the propatagium even before the origin of flight. On the other hand, the preserved angles of wrist joints in non-avian theropods are significantly greater than those in birds, suggesting that the avian interlocking wing-folding mechanism involving the ulna and radius had not fully evolved in non-avian theropods. Our study underscores that the avian wing was acquired through modifications of preexisting structures including the feather and propatagium.