(CNN) — Scientists say a very rare find of some 20 fossilized pterodactyls has produced the first clear evidence of a controversial theory of evolution.

This image shows the fossilized skeleton of Darwinopterus which was found in north-east China earlier this year.
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The fossils were found in northeast China earlier this year, embedded in rock dating back 160 million years, and have been called “Darwinopterus” after the renowned naturalist Charles Darwin.

The creature’s discovery has astounded scientists because their age puts them within two recognized groups of pterodactyls — primitive long-tailed forms and advanced short-tail forms — and they display characteristics of both.

The combination of features indicates that the primitive pterodactyls evolved relatively quickly, and that certain groups of features changed at the same time.