Key Wrist Bone Found in Bird Ancestors – Earlier Than Thought
Dinosaur Wrist Discovery Rewrites the Story of FlightS Evolution
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New research reveals a crucial anatomical shift in theropod dinosaurs that predates the evolution of flight, offering a deeper understanding of how birds acquired their aerial abilities.
Unlocking the Secrets of Dinosaur Wrists
Paleontologists have long been fascinated by the evolutionary journey that led from ground-dwelling dinosaurs to the feathered, flying creatures we see today. A groundbreaking study, published in the journal Nature, sheds new light on this transition by focusing on a tiny but significant bone within the dinosaur wrist: the pisiform.
The research, led by scientists from Stony Brook University and yale University, utilized exceptionally preserved fossil specimens to reconstruct the wrist anatomy of theropod dinosaurs. “We were lucky to have two immaculately preserved theropod wrists for this,” stated Alex Ruebenstahl, a paleontologist at Yale University.”Wrist bones are small and even when they are preserved,they are not in the positions they would occupy in life,having shifted during decay and preservation.”
The key to their breakthrough was the discovery of a migrated pisiform in a non-avian theropod. The pisiform, a small, pea-shaped bone, plays a critical role in the wrist’s ability to rotate and fold, essential for flight. “Seeing this little bone in the right position cracked it wide open and helped us interpret the wrists of fossils we had on hand and other fossils described in the past,” Ruebenstahl explained.
The Migrated Pisiform: A Precursor to Flight?
Dr. James Napoli, a vertebrate paleontologist and evolutionary biologist at Stony Brook University, highlighted the meaning of their findings. “We believe this is the first time a migrated pisiform in a non-bird meat-eating dinosaur has been identified,” he said.
the study suggests that this anatomical rearrangement, where the pisiform moved into a more central position within the wrist joint, occurred before the evolution of flight in many dinosaur lineages. “While we currently do not know precisely how many times dinosaurs learned to fly, it is intriguing that experimentation with flight in these creatures appears only after the pisiform migrated into the wrist joint,” Dr. Napoli commented.This migration may have laid the groundwork for the complex, automated wrist mechanisms seen in modern birds. ”Therefore, it is possible this established the automated mechanisms found in current living birds, though we would need to test this hypothesis with more research and analysis of dinosaur wrist bones,” he added.
Tracing the Evolution of Avian Traits
The research places this crucial wrist reorganization within the broader evolutionary context of theropod dinosaurs. The authors steadfast that the pisiform achieved its bird-like position not within birds themselves, but at the origin of Pennaraptora. This group of theropod dinosaurs is significant as it includes familiar species like Velociraptor (dromaeosaurids), troodontids, and oviraptorosaurs.
It is within the Pennaraptora that many classically “avian” traits,such as feathered wings,began to emerge. Flight itself evolved multiple times within this group, with estimates ranging from at least twice to possibly as many as five times.
A Deeper Theropod Ancestry for avian Wrists
The study’s findings indicate that the functional replacement of the ulnare bone by the pisiform happened much earlier in theropod history than previously understood, and it was a gradual, stepwise process. “Over the past few decades, our knowledge of theropod dinosaur anatomy and evolution has increased exponentially, much of it revealing that classically ‘avian’ traits such as thin-walled bones, an enlarged brain, and feathers, all characterize more inclusive groups of theropod dinosaurs,” the researchers stated.
This new understanding suggests that the unique structure of the avian wrist is not an isolated innovation within birds but rather a continuation of evolutionary patterns established much deeper within the theropod lineage,specifically with the origin of the Pennaraptora.The team’s thorough analysis, published on July 9, 2025, in the prestigious journal Nature, fundamentally reshapes our understanding of how dinosaurs evolved the anatomical prerequisites for flight, revealing a more ancient and complex evolutionary story than ever before.
Reference:
Napoli, J.G. et al. Reorganization of the theropod wrist preceded the origin of avian flight. Nature published online July 9, 2025; doi: 10.1038/s41586-025