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July 4
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Pennaraptor Tails by Albertonykus Pennaraptor Tails by Albertonykus
Rough drawings of rectricial morphology of select Mesozoic pennaraptors* in dorsal view. Not to scale.

*Pennaraptora is a newly-coined name for the group containing the last common ancestor of Oviraptor philoceratops, Deinonychus antirrhopus, and Passer domesticus and its descendants.

Oviraptorosaurs: Tails typically short, but very strong, likely to enhance use of tail feathers in visual displays. In Caudipteryx (and probably Protarchaeopteryx), a frond of feathers was present only at the tail tip, but Similicaudipteryx had large feathers along the entire length of the tail. A "bilobed" morphology where the feather frond was split into two distinct lobes on each side of the tail was once a popular interpretation for Caudipteryx, but this was based on the notion that the holotype specimen had preserved only one side of the feather frond. Newer interpretations suggest that both sides of the frond were preserved, though superimposed on top of one another.

Dromaeosaurids: Tails had limited vertical range of motion except at the base, but retained reasonable lateral flexibility. All specimens with well-preserved rectrices have a feather frond of sorts at the tip of the tail (and there is unpublished evidence that the frond in Microraptor extended down at least half the tail's length). A similar rectricial arrangement is seen in Scansoriopteryx. Some (but not all) Microraptor specimens preserve a pair of particularly long tail feathers at the tail tip.

Archaeopteryx: Rectrices form a large frond along the entire length of the tail. One well-preserved specimen shows a V-shaped split at the tail tip, but this may potentially have been the result of molting. Similar rectricial arrangements are seen in Jinfengopteryx and Anchiornis.

Jeholornis: Palm-shaped frond present at the tip of the tail, formed by narrow rectrices. A fan of coverts may have been present at the tail base, though there are many varying interpretations of this feature.

Epidexipteryx: Tail short with four very long ribbon-shaped rectrices attached.

Sapeornis: Among the most basal birds to have had a pygostyle homologous with that of modern birds. Preserved tail feathers have not yet been described, but one specimen that has them has been figured in this paper. Interestingly, the rectrices appear to form a fan, a feature not seen in some groups more closely related to modern birds.

Confuciusornithiforms and enantiornithines: Many had a pair of ribbon-shaped rectrices, but some individuals/taxa lacked them, probably reflecting sexual dimorphism. Some show marked oval-shaped expansions at the tips of their rectrices. Paraprotopteryx had four rectrices and Shanweiniao had at least as many (and potentially more). Shanweiniao is the only known taxon in which the rectrices overlapped at their bases, potentially conferring some aerodynamic function.

Euornithines: A tail fan with a muscular folding mechanism (as seen in modern birds) probably first evolved within euornithines. Many Mesozoic euornithines preserve the familiar fan-shaped tail, though, like in present day, there was variation upon this theme, such as the forked tail in Schizooura.

A non-exhaustive list of references on the evolution and function of maniraptor tails is given below.
-Clarke, J.A., Z. Zhou, and F. Zhang. 2006. Insight into the evolution of avian flight from a new clade of Early Cretaceous ornithurines from China and the morphology of Yixianornis grabaui. Journal of Anatomy 208: 287-308. doi: 10.1111/j.1469-7580.2006.00534.x
-Foth, C., H. Tischlinger, and O.W.M. Rauhut. 2014. New specimen of Archaeopteryx provides insights into the evolution of pennaceous feathers. Nature 511: 79-82. doi: 10.1038/nature13467
-Gatesy, S.M. 2001. The evolutionary history of the theropod caudal locomotor module. Pp. 333-347 in J. Gauthier and L.F. Gall (eds.), New Perspectives on the Origin and Early Evolution of Birds. Yale Peabody Museum; New Haven, CT.
-Persons, W.S., IV and P.J. Currie. 2012. Dragon tails: convergent caudal morphology in winged archosaurs. Acta Geologica Sinica 86: 1402-1412. doi: 10.1111/1755-6724.12009
-Persons, W.S., IV, P.J. Currie, and M.A. Norell. In press. Oviraptorosaur tail forms and functions. Acta Palaeontologica Polonica in press. doi: 10.4202/app.2012.0093
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"Among the most basal birds to have had a pygostyle homologous with that of modern birds."

Not if Foth et al's phylogenetic analysis is correct…

Do you remember if there was a reason they included Deinonychus in their definition of Pennaraptora? Was it to account for topologies with avialan oviraptorosaurs (which hasn't popped up since… what, Benton 2004)?
Albertonykus Featured By Owner Nov 17, 2014
They don't provide an actual reason for using Deinonychus. It may be to safeguard against avialan oviraptorosaurs, or (achieving the same result from a different perspective) to guarantee that deinonychosaurs are included.
alexandernevsky Featured By Owner Jul 8, 2014  Hobbyist Traditional Artist
This is extremely useful!  Well done for making the guide.
Albertonykus Featured By Owner Jul 8, 2014
Glad you find it helpful, and thanks for the watch!
raven-amos Featured By Owner Jul 7, 2014  Professional General Artist
Well done! I am really liking these guides you've been making!
Albertonykus Featured By Owner Jul 7, 2014
Thanks a lot!
Ornitholestes1 Featured By Owner Jul 5, 2014  Hobbyist Traditional Artist
So pennaraptora=chuniaoae? (I'm certain I spelled that wrong)
Albertonykus Featured By Owner Jul 5, 2014
Yes (and you didn't spell it wrong), but Chuniaoae has never been given a definition in the technical literature and there is reason to think that its original authors changed their minds about coining it at all, only leaving one use of it in the paper by accident.
sivesco Featured By Owner Jul 5, 2014  Hobbyist Photographer
Wow, those are some fancy tails! Are they all present in fossils?
Albertonykus Featured By Owner Jul 5, 2014
Yep, these are all based on specimens that preserve the tail feathers.
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