In eastern China, fossils of dinosaurs called Anchiornis have been discovered with their feathers intact. These specimens, 160 million years old, offer a unique opportunity to study the anatomy of wings from that period.
Researchers paid particular attention to a detail often overlooked: feather molting. In modern birds, the way feathers are replaced can indicate whether the animal depends on flight (explanation at the end of the article). An orderly process maintains wing symmetry, whereas an irregular molt is typical of species incapable of flight. By examining the fossils, the team was able to observe this pattern.
Dr. Yosef Kiat and his collaborators analyzed nine Anchiornis fossils. The preservation of the feathers allowed for the identification of the wing structure and new feathers in growth. Their study shows a disorderly molting pattern, indicating that these dinosaurs could not fly, an interpretation based on comparisons with modern birds.
160 million-year-old Anchiornis fossils.
Credit: Tel Aviv University
This observation informs us about the group Pennaraptora, feathered dinosaurs that are ancestors of modern birds (see below). Like contemporary ostriches or penguins, some members of this lineage may have abandoned flight following changes in their environment. This shows how adaptations can be reversible over time.
The research, published in Communications Biology, demonstrates that the evolution of wings was more diverse than previously thought. The simple detail of feather molting allows for the reconstruction of functional behaviors in ancient creatures, offering a new perspective on prehistoric fauna and its capabilities.
Feather molting in birds
Molting is the process by which birds replace their worn-out feathers. It is essential for maintaining the efficiency of flight or thermal insulation. In flying species, molting occurs in a gradual and symmetrical manner so as not to compromise flight capability. Conversely, in birds incapable of flight, such as the ostrich, molting can be more random and less organized.
This phenomenon is regulated by hormonal and environmental factors. The frequency and pattern of molting differ according to species and their needs. For example, migratory birds often synchronize their molt with their migration cycles to avoid losing important feathers during flight.
The study of molting in fossils, as with Anchiornis, allows paleontologists to deduce functional traits. By comparing with modern birds, they can infer whether a dinosaur was capable of flight or not. This approach provides a valuable tool for reconstructing the evolution of behaviors and adaptations.
Pennaraptora, a key link
Pennaraptora is a group of feathered dinosaurs that emerged about 175 million years ago. They include species like Anchiornis and are considered the direct ancestors of modern birds. This lineage is the only one among dinosaurs to have survived the mass extinction at the end of the Mesozoic era, 66 million years ago.
These creatures exhibited transitional characteristics, such as complex feathers and skeletal structures adapted for flight. Their study allows us to trace how avian traits, such as wings and beaks, gradually developed. Pennaraptora fossils, often well-preserved in China, provide important clues about this evolution.
The diversity within Pennaraptora indicates that evolution was not uniform. Some species may have developed primitive flight capabilities, while others lost them in response to environmental pressures.