Scales, Feathers, and Pycnofibres

Flight is probably one of the most fascinating and mysterious evolutionary traits ever developed, and it has been independently developed three times in the history of life on Earth: in the class Insecta, in the mammalian order Chiroptera (Bats), in the reptilian order Pterosauria, and in the superorder Dinosauria. These two latter groups are classified within the clade Avemetatarsalia (which means "bird metatarsals/metatarsi", a typical characteristic of the group members), which makes this clade extremely important to the study of the evolution of flight, at least from my point of view. Think about it, two of the three times that flight has evolved in vertebrates, only once has been in a group outside of this clade (even outside of the class Reptilia). Therefore, I would like to get my nose into the clade, and talk a bit about it.
Also known as Ornithosuchia, Ornithodira, and recently referred to by the name of Panaves, the clade Avemetatarsalia arose circa 245 million years ago, during the Anisian stage of the Middle Triassic, being Asilisaurus kongwe it oldest known representative, although recent records of ichnites from c. 252.3 m.y.a. indicate that the clade may have originated earlier than thought.

Asilisaurus kongwe
Image by NTamura

It covers the controversial group, Scleromochlidae, and Ornithodira, which includes both the clade Dinosauromorpha (Dinosaurs, its ancestors, and genera closely related), and Pterosauria. All groups being more related to Dinosauria than Crocodylia, unlike its sister clade, Crurotarsi, which holds crocodiles and their kin. Both within the famous clade, Archosauria.

In the end, only one group will survive the K-T extintion event.
Image courtesy of Dr. Mark Witton

I would also like to point out the similarities (presence of hair/feather-like filaments, endothermy, etc.), and the differences  between Dinosauria and Pterosauria, as well as their palaeoecological relationship, but I will leave that for later.