This ancient creature is a strange hybrid of a dinosaur and a bird – ScienceAlert

We can confidently say that birds are dinosaur descendants, although paleontologists are still baffled as to how this incredible evolutionary event occurred.

Now, a complete fossilized skeleton of a bird that lived in what is now China about 120 million years ago could help clarify key steps in the transformation process, featuring a more archaic, bird-like head dinosaur, on top of a body that has more in common with modern ones. birds.

The transition from dinosaur to bird included some of the most dramatic changes in form, function, and environment, eventually leading to the body plan that is typical of birds today.

Some of these changing features can still be seen how modern birds develop. But the order in which these changes occurred, and the nature of the evolutionary pressures that gave rise to strictly avian characteristics, is still open to debate.

The fascinating newly found fossil, named Cratonavi zhuican provide important information about the evolution of modern birds.

Investigators discovered the footprint on the body Cratonavisthe bird with a dinosaur head, during the excavations carried out in northern China.

Body prints of feathers dinosaurs and early risers, included Saint Confuciushave been discovered in this region, in sedimentary rocks formed about 120 million years ago, during the cretaceous period

Led by paleontologist Zhou Zhonghe of the Chinese Academy of Sciences (CAS), the scientists began their investigation of the fossil skull with high-resolution computed tomography (CT).

Using the digital versions of the mineralized bones, the team reconstructed the shape and function of the skull as it was during the bird’s life.

The result shows that the shape of the Cratonavis the skull is almost the same as that of the dinosaurs Tyrannosaurus Rex, and not like that of a bird.

“Primitive cranial features speak to the fact that most Cretaceous birds like now Cratonavis they could not move the upper beak independently of the braincase and lower jaw, a widely distributed functional innovation among living birds that contributes to their enormous ecological diversity.” he says CAS paleontologist Zhiheng Li.

The unusual combination of a dinosaur akinetic skull with a bird skeleton added to previous studies on the importance of evolutionary mosaicism in the early diversification of birds.

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Among the avian branches of the dinosaur family tree, Cratonavis is among the long tails Archaeopteryxwhich was more like a reptile, and the ornithothoraxwhich had already developed many of the traits of modern birds.

Also interesting is the fact of Cratonavis The fossil has a surprisingly long scapula and first metatarsal (foot bone), features rarely seen in fossils of other dino-ancestors of birds, and totally absent in modern birds.

Evolutionary trends show reduced length in the first metatarsal as birds developed.

The authors of the study propose that during the transition from dinosaurs to birds, the first metatarsal went through a process of natural selection that made it shorter. Once it reached its optimal size, which was less than a quarter of the length of the second metatarsal, it lost its former functions.

The unique feature of an enlarged metatarsal Cratonavis is more comparable to the Upper Cretaceous dragon, member of a group of feathered carnivores known as dromaeosaurids.

The elongated scapula has been observed previously in Cretaceous birds com Yixianornis i Apsaravis.

The fact that Cratonavis it had a very long scapula probably compensated by the fact that it did not have a sternum adapted to give the fleshy pectoral muscles a larger surface to attach to. This extinct species may have contributed to a biological experiment of flight behavior.

One of the lead authors, paleontologist Min Wang, explain “The elongated scapula could increase the mechanical advantage of the muscle for retraction/rotation of the humerus, which compensates for the overall underdeveloped flight apparatus in this early bird, and these differences represent morphological experimentation in the flight behavior early in the diversification of birds”.

The authors mention the abnormal morphologies of the scapula and metatarsals preserved in a Cratonavis highlight the breadth of skeletal plasticity in early birds.

Cratonavi zhui‘s unique combination of anatomy is not a step between two majestic categories of animals, but a sign of how all living things represent increments of change and the evolution of birds of all feathers occurred simultaneously throughout of a great variety of divergent paths.

The research was published in Nature Ecology and evolution.