|Xiaotingia zhengi type fossil|
Xiaotingia is very, very similar to Archaeopteryx. It is about the same size with a feathered body and fore-arms like a bird, but with long fingers ending in claws and a tooth lined beak. It is without a doubt, very, very closely related to Archaeopteryx. The problem arises not with its morphology. Instead it lies with Xiaotingia's taxonomic placement. Xiaotingia, despite its bird like characteristics, was still a dinosaur and part of Deinonychosauridae.
It is possible that, because Xiaotingia was very closely related to Archaeopteryx, but is still a dinosaur, Archaeopteryx was in fact on the dinosaur side of the line rather than on the bird side. While this might sound like some harebrained theory simply designed to discredit Archaeopteryx's evolutionary status. If we look at evidence other than taxonomy and morphology, it becomes far more likely.We know that Archaeopteryx lived during the late Jurassic. A bird requires a habitat where it can build a nest and raise young safe from predators.
The only high enough roosts would have been the tall pine forests. However pines do not make a very good point for nest building due to their spindly nature. The feeding action of giant sauropod dinosaurs such as Brachiosaurus or Diplodocus would have destroyed many of the trees also making the pine forests not viable as a roosting ground. If we look at these pieces of evidence, it becomes possible that Archaeopteryx was a dinosaur rather than a bird.
If this theory is correct, it means that the oldest known birds are creatures such as Sapeornis and Epidexipteryx. When I first saw the theory I was very suspicious. However when I read the papers and news articles, I realized that the evidence did make sense. The next couple of years could be very exciting as the dinosaur-bird lineage becomes more and more clear.