An important and contentious discovery is Archaeopteryx, found in southern Germany in 1861. It lived in the Late Jurassic Period around 150 million years ago, in what is now southern Germany during a time when Europe was an archipelago of islands in a shallow warm tropical sea, much closer to the equator than it is now. Archaeopteryx is considered by many to be the first bird, being about 150 million years old. It is seen as intermediate between the birds that we see flying around and the predatory dinosaurs like Deinonychus.

Unlike birds today, it had a full set of teeth, a rather flat breastbone, a long bony tail, "belly ribs" and three claws on the wing. However, its feathers, wings, "wishbone" and reduced fingers are all characteristics of modern birds.

Archaeopteryx had feathers, whether these feathers were used for regulating its body temperature or for flight is a matter still open for debate. The origin of flight, and the actual flight capabilities of Archaeopteryx, are still debated. It was roughly the size of a raven, with broad wings that were rounded at the ends and a long tail compared to its body length. Because it displays a number of features common to both birds and dinosaurs, Archaeopteryx has often been considered a link between them. Further research on dinosaurs from the Gobi Desert and China has since provided more evidence of a link between Archaeopteryx and the dinosaurs. It has been regarded as the first true bird, representing a major evolutionary step away from dinosaurs.

The discovery in China of Xiaotingiathe new fossil suggests that Archaeopteryx was just another feathery dinosaur and not the significant link that palaeontologists had believed.

The renowned Chinese palaeontologist Professor Xu Xing believes his new discovery Xiaotingia has finally knocked Archaeopteryx off its perch.

His team has detailed the discovery of a similar species, Xiaotingia, which dates back 155 million years to the Jurassic Period.

By carefully analysing and comparing the bony bumps and grooves of this new chicken-sized fossil, Prof Xu now believe that both Archaeopteryx and Xiaotingia are in fact feathery dinosaurs and not birds at all.

"There are many, many features that suggest that Xiaotingia and Archaeopteryx are a type of dinosaur called Deinonychosaurs rather than birds. For example, both have a large hole in front of the eye; this big hole is only seen in these species and is not present in any other birds.

They are very  similar to other Deinonychosaurs in having a quite interesting feature - the whole group is categorised by a highly specialised second pedo-digit which is highly extensible, and both Archaeopteryx and Xiaotingiashow initial development of this feature.

According to Prof Lawrence Witmer from Ohio University –

“Since Archaeopteryx was found 150 years ago, it has been the most primitive bird and consequently every theory about the beginnings of birds - how they evolved flight, what their diet was like - were viewed through the lens of Archaeopteryx.”

“So, if we don't view birds through this we might have a different set of hypotheses”

There is a great deal of confusion in the field says Prof Witmer as scientists try to understand where dinosaurs end and where birds begin.

“It's kind of a nightmare for those of us trying to understand it. When we go back into the late Jurassic, 150-160 million years ago, all the primitive members of these different species are all very similar.”

“So, on the one hand, it's really frustrating trying to tease apart the threads of this evolutionary knot, but it's really a very exciting thing to be working on and taking apart this evolutionary origin.”

Such are the similarities between these transition species of reptiles and birds that other scientists believe that the new finding certainly will not mean the end of the argument.

Prof Mike Benton from the University of Bristol, UK, agrees that the new fossil is about the closest relative to Archaeopteryx that has yet been found. But he argues that it is far from certain that the new finding dethrones its claim to be the first bird.

According to Prof Witmer, little is certain in trying to determine the earliest bird and new findings can rapidly change perspectives.

"The reality is, that next fossil find could kick Archaeopteryx right back into birds. That's the thing that's really exciting about all of this."