New clues that the origin of plumage goes back to at least 250 million years ago

An article published in the journal “Trends in Ecology & Evolution” reports new clues about the origin of plumage that confirm that it evolved starting from about 250 million years ago among some life forms that survived the devastating mass extinction that occurred at the end of Permian period. A team of researchers coordinated by the British University of Bristol combined information regarding fossils with others obtained through molecular biology analysis to obtain a conclusion that confirms a hypothesis made after the discovery of feathered pterosaurs.

The discovery over the last decades of several species of feathered dinosaurs and that species already known had at least a partial plumage indicated that plumage started evolving in dinosaurs. However, an article published in December 2018 in the journal “Nature Ecology & Evolution” reported the discovery of two specimens of pterosaur with filaments called pycnofibres that are an actual plumage and this led the authors to hypothesize a far older origin in a common ancestor of dinosaurs and reptiles.

Some team members who carried out the study on the feathered pterosaurs continued their research to test their hypothesis. In this new phase they also worked on fossils of Kulindadromeus zabaikalicus, a small herbivorous dinosaur that lived in present-day Siberia between 169 and 144 million years ago, in the Jurassic period. The image (Courtesy Andrey Atuchin. All rights reserved) shows an artistic reconstruction of this dinosaur in its lacustrine environment.

Various fossils of Kulindadromeus zabaikalicus have been discovered since 2010 and the species was identified in 2014. Some fossils are in an excellent state of preservation which includes skin covered in both scales and feathers, as reported by a team that also included some researchers who are studying the origin of plumage in an article published in July 2014 in the journal “Science”.

The discovery of Kulindadromeus zabaikalicus was interesting because this species was classified in the ornithischian (Ornithischia) order while feathered dinosaurs were part of the order of the theropod (Theropoda) suborder, part of the saurischian (Saurischia) order. The fact that plumage existed in dinosaurs with very distant relationships was already evidence that plumage started evolving long before early birds’ close relatives.

Danielle Dhouailly of the University of Grenoble, co-author of the research, works on the development of plumage in baby birds and stated that modern birds often have scales on their legs and neck with the same groups of genes that regulate the development of reptile scales, bird feathers and mammal hair. This is another piece of data based on genetics and molecular biology that is important in the research that shows how plumage may have evolved very soon.

Putting all the information together, the researchers confirmed the hypothesis that the origin of the plumage dates back to at least 250 million years ago. It was the beginning of the Triassic period, when the world was recovering from the most devastating mass extinction and the common ancestors of pterosaurs and dinosaurs were adapting to the new situation and then started diversifying.

Initially, primitive plumage was probably useful to isolate the body and keeping it warm, only a long time later the adaptations linked to other functions began. In essence, the study of the evolution of plumage, scales and hair is linked to that of other physical characteristics, from flight to the metabolism of warm-blooded animals, so research will continue also integrating various elements.

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