Draconia was diagnosed in 1978 by Irwin & Jones as "medium to large diapsid reptiles with three functional pairs of limbs, one of which has been modified into bat-like wings." Mooney (1962) noted that dragons have a strong tendancy toward secondary flightlessness. Extent Draconia is divided into several families: Eudracocidae, Palusodraconidae, Argosidae, Taurodracocidae, Harenadracocidae, Rugodracocidae, Chasmodracocidae, Dracolympidae, Cryodracocidae, and Felimimidae. As Irwin (1996) pointed out, virtually every genus of extent dragon is placed in its own family aside from members of the well-supported Eudracocidae. "The various extent species of dragons," he wrote, "come in a wide variety of disparate forms and are difficult to resolve in relation to one another."
The difficulties in resolving living dragon relationships are further impeded by the terrible fossil record for dragons. The oldest dragon fossils date back to the Early Cretaceous in the form of a partial skull from India. Protodracos rex (Hutchings, 1984) was a small dragon, estimated to be less than eight feet long, and was carnivorous. The skull is well preserved but fragmentary--only the portion in front of the orbits is known. However, it shows characteristic dragon features like a large recessed naris for fleshy outer nostrils, a short, squared-off snout, and evidence of external ornamentation. Strangely, Protodracos has heterodont dentition, with large fang-like teeth at the front of the jaw, and smaller alligator-like teeth behind the premaxilla. One of the best-known fossil forms is Ambulodracos franco (Crank, 2000), an enormous Paleocene form from France. Known from a partial, but skull-less, skeleton, Ambulodracos was thirty feet long and heavyset. It has small wings, and demonstrates that dragons grew very large and flightless early in their evolution. Dragons do not turn up again until the Miocene, where a potential ancestor of Harenadracos (Wilder, 2004) is known, as well as a Central African ancestor of Megalodracos (Bosley, 1923). There are other bits and pieces known from the Oligocene and Pliocene, but they are not worth mentioning here.
Irwin (1996) suggested that, among extent Draconia, the Taurodracocidae was the basalmost member, but that "it is far removed from its ancestral stock." Irwin surmised that among all flightless or semi-flightless forms, Tauropesa had the most atrophied flight aparatus. He also noted its long, sinuous tail, which he considered a primitive feature. The Cryodracocidae was regaled to a basal, but unresolved, position given its enormosity, extreme wing atrophy, and long tail. Similarly, Argos argos was placed in its own family and placed closer to other dragons than to Tauropesa or Cryodracos. Wing retention, a shorter caudal series, dorsal spines, and extreme cranial ornamentation were all reasons for this more inclusive grouping.
He also united Eudracos, Megalodracos, Feradracos, and Sinospondylus in a clade called Neodraconia, of which Sinuospondylus was the basalmost member. The other three are united in a monophyletic Eudracocidae consisting of (Eudracos + (Megalodracos + Feradracos). A fossil form from Spain named Protopaluso (Arnold, 1988) links the Palusdraconidae to the Neodraconia. Irwin & Jones (1978) believed that Chasmodracos fell close to, but not within, the Eudracocidae. Irwin (1996) felt that Chasmodracos was probably closer to the Neodraconia than Palusodracos, but was unsure of which taxon should be considered the outgroup. Irwin named a new group, Europadracoidea, to include an unsresolved triochotomy of Palusodracos, Chasmodracos, and the Neodraconia.
Irwin also considered the possibility that Harenadracos and Rugodracos shared a common ancestry, based prominantly on the presence in both of a rostral bone and triangular skulls in dorsal view. He named this unranked clade Rostrodraconia. Irwin had trouble finding places for Felimimidae and Spinodracos. He wrote that Felimimidae was "not well understood" (from an anatomical perspective) to warrant placing it among other dragons yet. Irwin also did not include the creature in his phylogeny but remarked that it shows some superficial similarities to Argos, including a noticable underbite and pattern of spines. Upon the discovery of Dracospartus in 2003, Krause created the Dracolypmidae to include it and Spinodracos. Fletch (2004) suggested that Spinodracos was, in fact, the most derived member of the Eudracocidae. This hypothesis may still be correct, although further serious investigations into dragon systematics have not been undertaken.
A larger problem than how extent dragons relate to one another may be how Draconia as a whole relates to the rest of the Diapsida. Although unquestionably diapsids reptiles, the Draconia is notoriously difficult to pin down from there. Dragons are clearly not archosaurs, as they lack antorbital and mandibular fenestrae, but they may be archosauriformes. The presence of a third set of limbs complicates the issue, in that the pectoral girdle has been modified far beyond its ancestral condition in order to facilitate the wings. Still, Jennings (1989) noted similiarities between the pectoral girdle of Drepanosaurus and Megalodracos. Irwin & Jones supported this view, cautiously suggested a sister-group relationship between the Drepanosauridae and Draconia. This view is bolstered by the idea that dragons originated in an arboreal environment, and must have had adaptations early on to move them through such a home. Irwin (1996), however, suggested a more general relationship among the prolacertiformes, noting a tendancy among that group toward arboreality, yet not showing the specialities of drepanosaurs.
Irwin, B. E. & Jones, D. (1978). Monophyly of the Draconia. Draconium 19(1): 25-59.
Irwin, B. (1996). A revised phylogeny of the extent Draconia. In A Brief History of Draconology (Suet & Svenson, eds.). Prince Rupert Press: 56-73.
Mooney, B. D. (1962). Does wing structure simplification lead to flightlessness? European Journal of Draconology 52(3): 368-381.
Hutchings, W. (1984). A Cretaceous origin for Draconia. Draconium 51(4): 487-495.
Crank, E. R. (2000). A large new fossil dragon from the Paleocene of France. European Journal of Draconology 101(4): 512-518.
Wilder, J. (2004). A potential dragon wing finger from the Gobi Desert. Natura Historia 411: 349-453.
Bosley, G. (1923). Megalodracos in Central Africa. European Journal of Draconology 13(2): 244-249.
Arnold, S. W. (1988). A Spanish relative of Palusodracos. Brevia (August): 45-51.
Krause, P. (2003). A heavily-armored Greek dragon. European Journal of Draconology 104(2): 308-329.
Fletch, F. R. (2004). A re-evaluation of the Eudracocidae. Draconium 45(4): 455-461.