Euparaves (5)

From the previous post:
The most parsimonious alternative is that the basalmost Euparaves were feathered, long-bony-tailed, flying primitive birds. And the ground-dwelling oviraptors and alvarezsaurids that came later, were secondarily flightless.

Is this a problem for the dinosaur to bird theory?

Indeed it is.
It is a problem because the oviraptors and alvarezsaurids are considered to be outgroups (intermediates) between dinosaurs and Euparaves. But if oviraptors and alvarezsaurids are descended from flying Euparaves, then there is no lineage from dinosaurs to Euparaves.

Basal Euparaves were four-winged. The hindlimbs were feathered and acted as additional wings (hindwings). They contributed to lift and control.
This is important because they contributed to the ability of the basal Euparaves to fly.

https://en.wikipedia.org/wiki/Tetrapterygidae

Tetrapterygidae (meaning "four-wings") is a group of four-winged dinosaurs proposed by Sankar Chatterjee in the second edition of his book The Rise of Birds: 225 Million Years of Evolution, where he included Microraptor, Xiaotingia, Aurornis, and Anchiornis.[1] The group was named after the characteristically long flight feathers on the legs of all included species, as well as the theory that the evolution of bird flight may have gone through a four-winged (or "tetrapteryx") stage, first proposed by naturalist William Beebe in 1915.[2] Chatterjee suggested that all dinosaurs with four wings formed a natural group exclusive of other paravians, and that this family was the sister taxon to the group Avialae, although most phylogenetic analyses have placed the animals of his Tetrapterygidae elsewhere in Paraves, such as Xiaotingia, Aurornis, andAnchiornis being placed in Avialae.[3]

https://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=4&cad=rja&uact=8&ved=0ahUKEwjNgIW0-o3KAhXBKh4KHZZZBVwQFgg1MAM&url=http%3A%2F%2Fwww.asbweb.org%2Fconferences%2F2012%2Fabstracts%2F529.pdf&usg=AFQjCNGssPFCAJ3XMsXRzpb6B37h1wR_Mg&sig2=_L19RDPlM7wYTfgSd8Flvg&bvm=bv.110151844,d.dmo
HINDWING FUNCTION IN FOUR-WINGED FEATHERED DINOSAURS

The evolution of powered flight in birds remains a contentious issue in vertebrate paleontology. The diminutive predatory dinosaur Microraptor gui preserves evidence of extensive, lift-generating feathers on each manus and forearm, but also preserves evidence of lift-generating feathers associated with the hindlimbs, effectively forming a pair of “hindwings”.