As Andrea Cau puts it (after being garbled by Google Translate), many depictions of "feathered dinosaurs" don't actually depict "feathered dinosaurs" but "dinosaurs with feathers". They don't really show how these dinosaurs were feathered in life, but take a traditional scaly dinosaur and stick it in a suit of feathers. In other words, they're the equivalent of sticking a human into a gorilla suit and calling it a gorilla. I don't remember where I heard that analogy first, but it sounds apt to me.
|This is supposed to be a chicken.|
It's not just non-avian maniraptors. Even the de facto "first bird" Archaeopteryx runs into this problem a lot. In reality, we have a decent amount of data on the plumage of these dinosaurs, and they certainly weren't scaly dinosaurs stuck in feathered suits. I briefly described in Part I what we presently know about the plumage of each non-avialian maniraptor for which evidence of feathers has been found. Incidentally, at least one thing I said in Part I is now probably outdated. I talked about how protofeathers, plumaceous feathers, and pennaceous feathers are all known in maniraptors. That is still true, but not in the way I described. A new study has shown that the feathers preserved in the feathered dinosaur specimens are likely more complex than typically thought. A (dead) European siskin was crushed in a printing press to simulate the preservation of the feathered dinosaur specimens, and it turned out that crushed pennaceous body feathers looked like plumaceous feathers or protofeathers. So the "protofeathers" and "plumaceous feathers" found on the bodies of oviraptorosaurs, deinonychosaurs, and basal avialians are likely actually pennaceous feathers, and the protofeathers in more basal maniraptors and other coelurosaurs are probably plumaceous feathers, or at least multiple filaments joined together at the base instead of single filaments. That leaves only the bristle-shaped EBFFs found in Beipiaosaurus (and possibly some undescribed basal coelurosaur taxa) as the only known monofilament feathers in maniraptors. Incidentally, the "ribbon-shaped" wing feathers reported in the juvenile Similicaudipteryx are likely just developing regular pennaceous feathers, while the ribbon-shaped tail feathers in many Mesozoic birds really are ribbon shaped, but the ribbon-shaped part is probably a specialized calamus instead of fused barbs as usually interpreted.
Several common and persistent characteristics of gorilla suit dinosaurs routinely find their way into reconstructions, even those that are otherwise perfectly accurate. Inaccurate wing feathers are one. All modern birds have a fairly uniform wing feather arrangement: tertials attaching to the humerus, secondaries attaching to the ulna, and primaries attaching to the second finger. Non-avian maniraptors and basal avialians don't appear to have had tertials, but aside from that all evidence so far shows that oviraptorosaurs and deinonychosaurs had a similar wing feather arrangement. Other than Caudipteryx zoui and the juveniles of Similicaudipteryx, all oviraptorosaurs and deinonychosaurs with preserved wing feathers have secondaries, and all, so far without exception, have primaries. (More basal maniraptors, such as therizinosaurs, didn't have actual wing feathers, just long protofeathers on the arms.) Possibly by far the most common error in depictions of plumage in oviraptorosaurs and deinonychosaurs is the lack of primary feathers. Although some speculate that certain taxa might have lost the primary feathers, this is typical wishful thinking. There is no evidence that this was the case. Even in flightless birds with short, stubby forelimbs, primary feathers remain, though they aren't easy to see because they "blend in" with the body feathers. Nor is there any reason to suppose that wing feathers would have gotten in the way of catching prey, as the palms and claws of theropods do not point the same way as the feathers do. On a related note, there is no evidence that the fingers of deinonychosaurs were scaly, even though just about everyone reconstructs them that way. As far as we know, even the fingers of deinonychosaurs were fuzzy, although oviraptorosaurs on the other hand appear to have had scales or naked skin on their fingers.
Another common error in reconstructions of feathered dinosaurs is stopping the head feathers at the snout, or worse, having scaly, lizard-like heads. Most of these reconstructions are evidently inspired by the fact that in modern birds, feathers stop at the snout. However, modern birds have beaks. In beakless maniraptors (including many Mesozoic birds), the feathers appear to go all the way down the snout, leaving only some naked skin at the tip. Of course, there are variations on this. Beipiaosaurus appears to have had a naked face, and many modern bird clades have evolved naked faces. Even so, there is no reason think that any maniraptor re-evolved scales on previously feathered parts of the body, even if they might have secondarily lost their facial feathers. By the way, although it is common to speculate that carnivorous non-avian maniraptors had bald heads, this appears to be based on vultures, and as I discussed briefly in Part V, bald heads in vultures have more to do with soaring habits than with feeding behavior.
|Fossil of Eoenantiornis buhleri showing feathered snout photographed by Laikayiu, from Wikipedia.|
Finally, in paleo art, it's common practice to "show all work" and make sure all the skeletal features and proportions of a dinosaur can been seen in reconstructions. However, as Matt Martyniuk, Mickey Mortimer, and Dr. Darren Naish discuss in the comments here, restoring feathered dinosaurs means "obscuring your research". Just look at how much feathers can cover up skeletal features in modern birds! Fossils of non-avian maniraptors also show obscuring of skeletal features by plumage. (Take a look at the fossils of "Dave" or Beipiaosaurus I posted back in Part I.) Even in featherless dinosaurs, the presence of soft tissues would mean that they were far from the shrink-wrapped creatures commonly depicted in art.
|Museum mount of Strix nebulosa showing extent of plumage, photographed by FunkMonk, from Wikipedia.|