Ok, briefly:

The closest non-avian relatives of the birds are the Deinonychosaurs, which together comprise a clade called Paraves. This group includes many small meat-eating dinosaurs including the famous Velicraptor and the four-winged Microraptor. Also included are all birds, from both extant and extinct lineages including basal birds such as Archaeopteryx and Anchiornis. All of these were feathered, and in fact all coelurosaurs were probably feathered as large, feathered tyrannosaurs are also known.

The features that birds have were not acquired in a single evolutionary jump, but accrued incrementally over hundreds of millions of years of evolution; the way birds breathe, long considered unique, is very similar to the crocodile respiratory system for example, so both of these archosaurs shared a common ancestor. We also know feathers aren't restricted to birds, and neither did flight arise in birds either as many other dinosaurs could fly, Microraptor for example (although this wasn't powered flight, more refined gliding). Early birds had teeth (chicks are occasionally born with teeth today) and clawed wings - as many modern birds do; they retain claws on their first digit - look closely at your chicken wings before eating and sure enough there's a tiny claw visible.

This means the exact point where the most basal bird appears isn't clear; the transition is subtle and even Archaeopteryx has been punted out of birds and then back in based on the possibility that advanced deinonychosaurs and the carnivorous early birds might actually belong with together and not with basal birds, who might have been herbivorous. In some respects, this wonderfully complex puzzle becomes more baffling as we find more fossils. There is no clear line between avian and non-avian dinosaurs because all these fossils are transitional and are of very closely related taxa.

Be assured, this story is a long way from being over. The origin of birds has long been a question that fascinates palaeontologists and this research and debate will continue. There are issues with the completeness of the record, and the fact that Lagerstätten can create a sampling bias, and of course we are finding new fossils all the time. We understand that birds are derived maniraptorian dinosaurs, but we're still not sure when or where this occurred.

Not bad work considering we're only been at it for 150-odd years. Huxley would have loved to have been involved with this research, and would rightly be pleased that he has been vindicated by the work of countless palaeontologists and other scientists.

Soapy Sam might not be so pleased. Creationists are still trying to skew the science to accommodate a simplistic and rather dull narrative, despite essentially not changing their arguments for over a century whilst science moves on. Picking a dinosaur and yelling "bird!" is not science.

The spirit of Darwin's bulldog lives on.*


*boom-ta!