Dinosaurs and birds developed flying capacity independently

The fossil, named Norellraptor barsboldi, analyzed by an international team of scientists from China and Italy and described on Tuesday in an article published in Nature Communications, changed what was known about how dinosaurs conquered the skies.

The specimen of microrraptorine (small dinosaurs with feathers and wings), exceptionally well preserved, was discovered in the geological formation Jiufotang (China), a site of the Lower Cretaceous with ages between 145 and 100 million years.

Microtraptorines were small predatory dinosaurs similar to birds and relatives close to them.

Fossils discovered so far (most of them in China) showed that some micro-spreads had long feathers on both their previous and later limbs, suggesting that they could be adapted for flight.

For a long time, paleontologists debated whether the ability to fly or glide arose only once in the common ancestor of the Paraves (the group that includes the microrraptorines and birds) or whether the characteristics necessary for this evolved independently on multiple occasions.

The study described a 57 cm fossil that preserves parts of its plumage and that, according to the analyses, it was at least three years old when it died.

By comparing the flight characteristics of the new fossil with those of other microrraptorines and those of the primitive bird line (Avialae), it was found that these small carnivores and primitive birds shared 57 morphological characteristics related to the flight, which represents approximately 30% of the fundamental physical traits needed to fly.

However, despite sharing a large number of structures, researchers believe that birds and dinosaurs did not inherit a unique “project map”.

Instead, they developed their flight devices in a completely “independent and convergent” way in response to similar needs and different evolutionary pressures.

For the authors, the main evidence of this separation lies in the order in which their bodies evolved, which was completely opposite, in the line of birds, evolution first transformed the scapular waist and the wing joints before changing the hand.

In microraptorines, such as Norellraptor, the first transformations consisted in shortening the bones of the fingers to reduce their grip function. Only a long time later did the elongated sternum and the shoulder changes appear.

For the authors, this divergence in the temporal sequence of changes demonstrates that there was no latent or shared genetic model that guided both groups.

In addition, microscopic analysis of the bones of Norellraptor's arm revealed that his limbs grew at discontinuous and very particular rhythms.

This osteohistological pattern differs from the developmental mechanisms observed in current flying birds, which confirms that the wings of microraptorines formed under their own biological dynamics.

The study on the Norellraptor lays down the paradigm of the unique origin of the flight and reveals that the ability to fly was not a unique innovation in the history of dinosaurs, but rather an “evolutionary experience” that nature successfully repeated by totally different paths, highlighted the study.