The forebrain of the dinosaur Zanabazar junior is already similar to a bird (Amy Balanoff / AMNH)
For a long time the difference between birds and dinosaurs seemed clear: birds have feathers and can fly, dinos do not. But this separation softens more and more, at least since more and more fossils of feathered dinosaurs were found. Now it turns out that these Cretaceous dinosaurs also came close to the birds in another way: Many of them already had a similarly enlarged forebrain as today's birds - and thus had quite the neurological prerequisites to rise into the air.

The brain of today's birds is perfectly adapted to the complex requirements of flying: it magnifies strikingly the areas responsible for processing optical information and coordinating body movements. "The rate of this encephalization is six to eleven times higher than in other groups of animals, " explain Amy Balanoff of the American Museum of Natural History in New York and her colleagues. A similar enlargement of the brain in relation to body size otherwise only exists in mammals. In the birds, this neural growth began early in their evolutionary development: For example, the "primitive bird" Archeopteryx already has a brain that lies in its volume relative to the size of the body between that of early dinosaurs such as the Tyrannosaurus rex and today's birds, like the Researchers report.

In their study, Balanoff and her colleagues wanted to explore more closely whether Archeopteryx is really an intermediate link between birds and dinosaurs in this regard, or perhaps other, closely related dinosaurs already possessed the typically enlarged forebrain. To clarify this, the researchers studied the fossil skulls of two dozen feathered dinosaurs, including the Archeopteryx, and some modern birds using computed tomography and created 3D models of their brain shells. They then determined the total volume of the brains of these species in relation to body size, and measured the sizes of certain brain regions such as the cerebrum and the bulge of the visual and olfactory center.

Bigger than Archeopteryx

It turned out that some of the feathered dinosaurs possessed even larger brains in proportion to their height than Archeopteryx. "This species is often considered a unique link between feathered dinosaurs and birds, " says Balanoff. But this proves that he at least in terms of brain volume by no means had a special position. Instead, some Oviraptors and also the Deinonychosaur Zanabazar junior trumped him. The disproportionately large areas of the brain, such as the forebrain, cerebellum and optical centers, are larger in some of these dinosaurs than in Archeopteryx. display

The researchers draw two conclusions from these results: First, there is no clear, on the size or anatomy readable separation between the typical bird brain and that of its predecessors. Instead, brain enlargement began even before the development of the first true primitive birds - or these features developed independently in different dinosaur groups. On the other hand, some non-bird dinosaurs may have already possessed the neurological prerequisites for flying. "If Archeopteryx had a brain ready to fly - which was pretty much the case - then at least some of the other closely related dinosaurs had it, too, " Balanoff said. This supports theories that some of the four-winged Deinonychosaurs, including Microraptor zhaoianus and Anchiornis huxleyi, may have already mastered short gliding flights.

Source:

  • Amy Balanoff (American Museum of Natural History, New York) et al., Nature, doi: 10.1038 / nature12424
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