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 All specimens with well-preserved rectrices have a feather frond of sorts at the tip of the tail (and there is unpublished evidence that the frond in Microraptor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
: 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. (A very well preserved specimen figured in this review paper
strongly suggests to me that a covert fan was indeed present.)Epidexipteryx
: Tail short with four very long ribbon-shaped rectrices attached.Sapeornis
: Potentially among the most basal birds to have had a pygostyle homologous with that of modern birds. The tail frond is fan-shaped due to the short length of the tail, but it almost certainly was not a mobile folding fan as seen in modern birds. This may represent the basal condition for short-tailed avialans.
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. The rectrices of most well-preserved specimens show barbs present only at the tips, but those of Eopengornis
have barbs present along the entire length. They may represent a transitional morphology between a Sapeornis
-like rectricial arrangment and that of "typical" enantiornithines (a shift that happened independently in confuciusornithiforms).
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 tails in Schizooura
that were achieved using different rectricial arrangements.
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. 2014. Oviraptorosaur tail forms and functions. Acta Palaeontologica Polonica 59
: 553-567. doi: 10.4202/app.2012.0093
-Wang, X., J.K. O'Connor, X. Zheng, M. Wang, H. Hu, and Z. Zhou. 2014. Insights into the evolution of rachis dominated tail feathers from a new basal enantiornithine (Aves: Ornithothoraces). Biological Journal of the Linnean Society 113
: 805-819. doi: 10.1111/bij.12313