Bird dinos and dino birds

Read more: Living dinosaurs: How birds took over the world

The feather that stirred up the whole debate (Image: O. Louis Mazzatenta/NGS Image Collection)

Only now can we say beyond reasonable doubt that birds don’t just have anatomy like dinosaurs – they are dinosaurs

Almost as soon as archaeopteryx was discovered, scientists noticed its striking anatomical similarity with dinosaurs. Yet it has taken until now to establish beyond reasonable doubt that this is because birds are dinosaurs.

Darwin’s friend Thomas Huxley first championed the idea of a bird-dinosaur relationship back in the 1860s. However, the idea fell out of favour in the early 20th century when Gerhard Heilmann, a Danish artist and scientist, published a hugely influential book, The Origin of Birds, arguing that birds evolved directly from a primitive archosaur, a reptilian group which also gave rise to dinosaurs, pterosaurs and crocodiles.

Heilmann’s key point was that theropods – the suborder of dinosaurs containing the species that archaeopteryx most resembled (see chart) – did not have the collarbones that are fused in birds to form the wishbone, or furcula. This led him to conclude that birds could not have evolved from theropods as it would have meant losing their collarbones and then re-evolving them. This view dominated for most of the 20th century.

Opinion began to swing back towards the dinosaurs in the 1970s, when John Ostrom of Yale University noted that a small predatory theropod named deinonychus had particularly striking anatomical similarities to archaeopteryx. Later work confirmed that birds share dozens of anatomical features with theropods, and are especially similar to two families, the dromaeosaurs (including …