In the vein of recent discussions involving enigmosaurs and alvarezsaurids, I figured I'd present a similar case as an example of how easy it is to make an alternative phylogeny. This phylogeny is supported by good synapomorphies, but is less parsimonious than the currently accepted one.
I suggest confuciusornithids are in fact volant oviraptorids. This is supported by the following characters-
1. toothless premaxilla
This is actually more parsimoniously seen as a confuciusornithid-oviraptorid character. Otherwise, two steps would be required when oviraptorids and confuciusornithids each developed this convergently (with ornithurines too).
2. toothless maxilla
The situation is similar to the above, but even more so, as toothless maxillae didn't evolve until neornithines. Also in the more basal Chirostenotes and Caudipteryx.
3. toothless dentary
Just like the toothless maxilla. Also in the more basal Chirostenotes and Caudipteryx.
4. elongate external mandibular fenestra (>24% of mandibular length)
Unique to confuciusornithids, oviraptorids, Chirostenotes and Caudipteryx.
5. process of surangular process invades external mandibular fenestra
Only found in confuciusornithids and oviraptorids among theropods.
6. maxilla reduced compared to premaxilla
May have developed as early as Caudipteryx. Not seen in other non-ornithurine birds.
7. extensive dentary symphysis
Known in Chirostenotes, oviraptorids and confuciusornithids. This is absent in non-neornithine birds.
8. rod-like jugal
In oviraptorids and confuciusornithids.
9. double-headed quadrate
In confuciusornithids, oviraptorids and probably Chirostenotes. Would help explain why Sinornis, Patagopteryx and hesperornithiformes have single-headed quadrates.
10. two elongate posterior dentary processes
Only seen in oviraptorosaurs and confuciusornithids.
11. nasals strongly reduced in size
Present in confuciusornithids and oviraptorids, but not in basal birds like Eoenantiornis or Sinornis.
12. seven sacral vertebrae
Like Ingenia, a possible sister group to confuciusornithids within the Oviraptoridae.
13. fused sternal plates
Again, known in Ingenia.
14. manual ungual II much smaller than I
Another synapomorphy indicating Ingenia the confuciusornithid sister group, not known in any other theropod.
Note that confuciusornithids' fused scapulocoracoid fits better with this hypothesis, as the traditionally more basal Rahonavis has an articulated scapulocoracoid. Similarily, Confuciusornis has a poorly developed acromial process, unlike other basal birds and eumaniraptorans. Also note the similar reduction in maxillary fenestrae, similarily shaped dentary, boomerang-shaped furcula (not seen in Velociraptor, Caudipteryx, etc.).
Many supposedly avian characters are also developed in at least some oviraptorosaurs (naris larger than antorbital fenestra, pygostyle, less than thirteen dorsal vertebrae, less than twenty-five caudal vertebrae, radius longer than 90% of humeral length, proximally fused metatarsus, reversed hallux), showing these aren't reliable avian synapomorphies of confuciusornithids. Most of the remaining synapomorphies are directly related to flight, so were probably developed in parallel to true birds for that reason.
I propose referring to Confuciusornis and Changchengornis as members of the Confuciusornithinae, as they are within the family Oviraptoridae. This makes the so far unnamed clade Enigmosauria + Paraves the Pygostylia.
| |--"other oviraptorids"
What's everyone think? ;-)