Feathered Dinosaur - Phylogeny and The Inference of Feathers in Other Dinosaurs

Phylogeny and The Inference of Feathers in Other Dinosaurs

Fossil feather impressions are extremely rare and they require exceptional preservation conditions to form. Therefore only a few feathered dinosaur genera have been identified so far. However, through a process called phylogenetic bracketing, scientists can infer the presence of feathers on poorly-preserved specimens. All fossil feather specimens have been found to show certain similarities. Due to these similarities and through developmental research almost all scientists agree that feathers could only have evolved once in dinosaurs. Feathers would then have been passed down to all later, more derived species (although it is possible that some lineages lost feathers secondarily). If a dinosaur falls at a point on an evolutionary tree within the known feather-bearing lineages, scientists assume it too had feathers, unless conflicting evidence is found. This technique can also be used to infer the type of feathers a species may have had, since the developmental history of feathers is now reasonably well-known.

The scientists who described the (apparently unfeathered) Juravenator performed a genealogical study of coelurosaurs, including distribution of various feather types. Based on the placement of feathered species in relation to those that have not been found with any type of skin impressions, they were able to infer the presence of feathers in certain dinosaur groups. The following simplified cladogram follows these results, and shows the likely distribution of plumaceous (downy) and pennaceous (vaned) feathers among theropods. Note that the authors inferred pennaceous feathers for Velociraptor based on phylogenetic bracketing, a prediction later confirmed by fossil evidence.

Since 2002 feathers have been attested from additional lineages, covering nearly all of the major groups of the Tetanurae; however, as of 2012, no feathered Ceratosaurian (mostly of the Southern Hemisphere) has been discovered. Pennaceous feathers in adults are now attested down to the Ornithomimosauria. The following cladogram is adapted from Weishampel et al., 2004.