A unique study has for the first time documented the common process of a sequential feather replacement (feather molting) found among modern birds in a winged dinosaur dating back 120 million years. This finding has just been published in the journal Current Biology.
The finding shows that the dinosaur had highly-develop aerodynamic properties and may have lived in a habitat in which it faced predation risk or that it needed to maintain its flight capacities during molting. “It is fascinating to see how a mechanism that began to develop at least 120 million years ago also exist in today’s birds. It is also fascinating to see how we can use our modern knowledge about this mechanism in order to yield insights into the evolution and ecology of a dinosaur that lived 120 million years ago,” comments doctoral student Yosef Kiat of the Animal Flight Laboratory in the Department of Evolutionary and Environmental Biology at the University of Haifa, who led the study.
Birds must replace their feathers periodically in order to maintain their proper functioning. Once a feather reaches its full size it becomes a dead organ; the bird must then shed the old feather and sprout a new one in its place to ensure that its plumage remains functional – for example, for the purpose of flying. This process is known as molting. The molting strategy may indicate an ability to fly and provide clues about birds’ habitat. In species that spend much of their time in flight or in habitats exposed to predators (such as open areas with sparse vegetation that do not provide hiding places from predators), molting takes place in a gradual, sequential and slow manner in order to ensure that the birds maintain their flying capabilities even during the molting process. In birds that do not fly often, or that have access to numerous hiding places from predators without needing to fly, the process can be very rapid – the bird sheds a large number of feathers simultaneously and the entire molting process takes just two to three weeks.
The research team comprised doctoral student Kiat; his supervisor Prof. Nir Sapir, who heads the Animal Flight Laboratory in the Department of Evolutionary and Environmental Biology at the University of Haifa; and Amir Balaban, a senior ornithologist and director of the Urban Nature Division in the Society for the Protection of Nature in Israel and of the Nili and David Jerusalem Bird Observatory. Importantly, the Israeli team collaborated with internationally acclaimed paleontologists from China who included Prof. Xing Xu, a prominent researcher in the study of flying dinosaurs, together with Prof. Jingmai O’Connor and Prof. Min Wang, all from the Key Laboratory of Vertebrate Evolution and Human Origins and the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences. The team took the above-mentioned knowledge and sought to apply it to the Microraptor, a dinosaur that lived 130-120 million years ago and whose fossils have been found in China.
When we say that the team “took” this knowledge – we mean it literally. Kiat and Balaban flew to China to closely examine a fossil that rather unusually retained the fossilized marks of its wing feathers. “Naturally it’s by no means a routine matter to find a relatively complete dinosaur fossil, but it’s even rarer to find well-preserved fossilized wings. The feathers do not usually survive the fossilization process, but in this particular case most of the wing feathers can be seen very well,” Kiat explains.
“We are used to examining and studying molting in our regular bird ringing work. Coming face to face with a flying dinosaur that sunk into a primeval swamp millions of years ago is a very rare and exciting event. We are waiting eagerly for the Coronavirus to fade away so that we can return to the fossil storerooms across China and find additional milestones in the development of modern-day birds,” comments Amir Balaban, a member of the research team from the Ariel Pavilion at the Jerusalem Observatory.
After the researchers arrived in China, they slowly and methodically examined the fossil in order to determine whether there was any evidence of molting. Naturally, the chemical processes that have occurred over millions of years make this task much harder. “At first glance six feathers of differing sizes can be seen. However, we had to see whether we could be certain that these really are feathers of different lengths that are part of the molt process, rather than a feather that broke or was shortened for some reason. After some hard work, we managed to identify the borders of the feathers and to confirm that we were indeed looking at a wing that has feathers of several different lengths in a sequence. In other words, the Microraptor replaced its feathers in a gradual manner,” the researchers explain.
The researchers go on to point out that the finding not only shows that this ancient dinosaur used its feathers to fly, but also that it spent a relatively long time in the air and apparently relied on its flying ability in order to hunt for food or evade predators. In addition, it required this capability on a daily basis, including during the molting process. Until now, there has been a lively debate among scholars regarding the flying abilities of the Microraptor and of its aerodynamic performance. The new finding supports those the claim that the Microraptor could fly – and could fly well. “Our ability to take the molting process and draw conclusions regarding the dinosaur’s capabilities and habitat is fascinating. We see here an important feature in the life cycle of modern-day birds that is present in exactly the same way in dinosaurs – the most ancient reptiles,” the researchers conclude.