Photo provided by Beijing Museum of Natural History shows the restored Microraptor.

 

When did ancient birds and feathered dinosaurs start to molt, and how? Researchers from China and Israel have jointly unveiled the mystery.

According to research published in the journal Current Biology, ancient birds began to molt sequentially at least 70 million years ago so that they could maintain their flight ability through all seasons.

Feathers not only help birds to fly, but also help them maintain their body temperature. They also serve as an important tool for visual communication with other birds due to their colorful features.

As old feathers wear away and their various functions deteriorate over time, birds have to replace their feathers, or molt.

Previous studies indicated that different species of extant birds vary in their molting strategies, sequentially and non-sequentially, correlating with habitat selection and flight ability, according to a report by the Science and Technology Daily.

Through sequential molts, birds replace their feathers gradually and symmetrically between their two wings. The ordered and slow molts help birds maintain their flight ability throughout the entire year.

With non-sequential molts, birds replace all their wing feathers at once, resulting in an inability to fly during the period. Some birds that are unable to fly, such as the flightless cormorants from the Galapagos Islands, replace their feathers irregularly or without a predictable sequence.

To study the molting strategies of ancient birds, researchers from the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) under the Chinese Academy of Sciences together with peers from the University of Haifa in Israel jointly collected feather molt data from a total of 302 extant bird species.

Among the studied species, 51 were flightless birds, 61 were flightless only during the molting period, and 190 were flying species that can maintain their flight ability throughout the entire year.

By setting the data in the framework of the phylogeny of modern birds, they discovered that the earliest birds, at least 70 million years ago, molted sequentially.

They also found that some extant bird species that replace their feathers simultaneously or irregularly may have later evolved independently from their ancestors with sequential molting behavior. The change would have urged the species to select special habitats due to the loss of flight ability, thus avoiding danger.

The researchers also studied numerous feathered dinosaur fossils which were collected by the IVPP.

They discovered evidence of sequential molting behavior in a fossil specimen of Microraptor, a four-winged dinosaur that lived in the Early Cretaceous period about 120 million years ago.

The discovery confirmed that Microraptor may have had stable flight ability through all seasons.

The sequential molting behavior also showed that the environment Microraptor lived might have lacked the necessary conditions to provide it with protection, such as sufficient food resources, during molting. It might have also faced continuous pressure as prey.