While wings are typically highlighted in the exploration of the relationship between dinosaurs and birds, two paleontologists from Yale focus on a different aspect: drumsticks. They suggest that changes in the fibula of certain dinosaurs tens of millions of years ago contributed to how peacocks strut, penguins waddle, and turkeys trot.
“To grasp this better, think about drumsticks, like those served during Thanksgiving,” stated Armita Manafzadeh, the leading author of a recent study published in Nature. She is a postdoctoral researcher involved with Yale’s Institute for Biospheric Studies, the Department of Earth & Planetary Science, and the Yale Peabody Museum.
“In a drumstick, beneath the meat, there are two main bones: the tibia, which is long and strong, and the fibula, which is shorter and thinner,” explained Manafzadeh. “This shorter fibula is essential for birds, enabling them to twist and turn when not flying. To uncover its evolutionary background, we must examine dinosaurs.”
However, the fibula has often been overlooked by paleontologists and other researchers, frequently regarded as just a minor remnant of a larger anatomical structure. The concept that the shortened fibula had specific evolutionary advantages has been relatively unexamined.
“Generally speaking, the fibula is the smaller of the two lower leg bones and is often overlooked in the study of vertebrate structure and function,” noted Bhart-Anjan Bhullar, an associate professor of Earth and planetary sciences at Yale, as well as an associate curator at the Yale Peabody Museum and co-author of the study. “But evolution influences all parts of the anatomy, big and small. Structures that have been disregarded can provide valuable insights and undiscovered stories.”
For their research, the scientists utilized X-ray videos of a contemporary bird—a helmeted guineafowl—to meticulously analyze the poses of the bird’s knee joints. With advanced computer animation software, they integrated these videos with 3D models to depict how the bone surfaces aligned and worked together during movement.
They also gathered X-ray footage of an iguana and an alligator, in addition to examining the leg bone structures of various birds, including a penguin, an ostrich, an owl, and a crane.
The findings revealed that in birds, the tibial joint surfaces form curved arcs, allowing the shortened fibula to roll within the bird’s drumstick for approximately its full length relative to the tibia. These traits together enable the knee bones to maintain seamless contact, even when the joint rotates beyond 100 degrees.
“It’s evident that the fibula in birds operates quite differently than in other living reptiles,” Manafzadeh said. “This unique motion of their knees allows them to more effectively navigate their environment. They employ this flexibility for turning and moving on the ground, and we believe it may also play a role in mating rituals, capturing prey, and climbing around tree branches.”
Next, the researchers sought to trace the evolutionary beginnings of the shortened fibula in birds and found their answer in specific dinosaur species.
While many dinosaurs, like Tyrannosaurus rex, had straight tibial surfaces and rigid drumsticks that permitted only basic knee movements, some avian ancestors, including Rahonavis ostromi and Ichthyornis dispar, exhibited curved tibial surfaces and a thinner, independent fibula.
“We discovered that the features originally present in early dinosaurs, which reinforced the legs, were later adapted by birds and their relatives to enhance knee joint mobility in a distinctive and extreme manner,” Bhullar stated. “Time and again, evolution reuses existing structures and functions, often in unexpected and remarkable ways.”
The researchers emphasized that several notable fossils from the Yale Peabody Museum were crucial to their work, including Allosaurus, the massive Jurassic predator discovered by O.C. Marsh (which had a rigid dinosaur knee); Deinonychus, commonly referred to as the “velociraptor” from the “Jurassic Park” movies (which showcased early features of bird-like knee joints); and Ichthyornis, whose proto-beak was the focus of an earlier study by Bhullar (and which had a fully developed modern avian knee).
This study contributes to the ongoing research by Bhullar and Manafzadeh into the evolution of animal movement, utilizing their innovative approach to visualize how ancient creatures moved by comparing their joint structures with those of modern counterparts.
