Dinosaurs of a Feather

From Smithsonian Blog Dinosaur Tracking: Dinosaurs of a Feather

Poet Emily Dickinson once wrote, “Hope is the thing with feathers.” To fossil bird expert Alan Feduccia, however, anything with feathers is a bird and emphatically not a feathered dinosaur.

For decades Feduccia has been one of the most prominent members of a small and steadfast group of researchers who reject the growing body of evidence that birds are the descendants of one lineage of feather-covered coelurosaurian dinosaurs (the large and varied group which included tyrannosaurs, oviraptorosaurs, deinonychosaurs, therizinosaurs and others). Feduccia and like-minded peers have been provided no solid alternate hypotheses about where, when, why and how birds originated—they point to some yet-unknown lineage of creatures that might have lived more than 200 million years ago—but they insist that birds cannot be dinosaurs. Yet Feduccia’s argument in his new book Riddle of the Feathered Dragons is not quite that simple. Near the book’s conclusion, Feduccia writes “if [a creature] has avian feathers, it is a bird”—a view popular among dinobird denialists that some dinosaurs were, in fact, “hidden birds.”

Non-avian, feathered dinosaurs have been known to paleontologists since 1996. In the 16 years since the first such creature was found—a small theropod dinosaur preserved with fuzzy protofeathers and named Sinosauropteryx—scores of plumage-bearing dinosaur specimens have been discovered. These creatures exhibit a variety of different feather types, which has helped paleontologists, ornithologists and developmental biologists understand how feathers went from simple, wispy structures to complex, asymmetrical feathers that allow birds to fly.

Feduccia disagrees. He says that the protofeathers on Sinosauropteryx and other dinosaurs are, instead, collagen fibers from inside the animal’s body. This would keep dinosaurs comfortably scaly for those who don’t like the idea that birds are derived dinosaurs. But a number of coelurosaurian dinosaurs, such as Anchironis, Microraptor and others, have been preserved with more complex feathers that more closely approximate those seen on living birds. These structures cannot be simply cast off as collagen fibers or other quirks of preservation, and so Feduccia makes a strange argument. Microraptor and kin are not dinosaurs, Feduccia argues, but are instead birds that lost the ability to fly and were molded into the form of dinosaurs through a circuitous evolutionary pathway. By employing a very narrow definition of what a feather is, and by asserting that only birds can have feathers, Feduccia tries to rearrange evolutionary relationships through semantics.

When Sinosauropteryx was discovered, the dinosaur seemed to be an enigma. Paleontologists were not optimistic about the prospect of finding dinosaurs with feathers. Such intricate structures would only be recovered in instances of exceptional preservation. But additional discoveries since 1996 have confirmed that the find was not a fluke. And the fuzzy structures preserved along the backs of these dinosaurs contain an important clue that they are, in fact, protofeathers. In 2010 a pair of papers was published regarding the reconstructed feather colors of dinosaurs. These findings were based on melanosomes—microscopic organelles found in feathers that, depending on their shape and distribution, create different colors and sheens. Such structures would be expected in feathers, but not collagen, and so when paleontologists were able to identify melanosomes in the fuzz of Sinosauropteryx, they provided new evidence that the dinosaur carried protofeathers.

Perhaps more importantly, however, there is no indication that creatures such as Oviraptor and Velociraptor were birds. Analysis after analysis has found them to be unequivocal, non-avian dinosaurs within the coelurosaur subgroup. Although Feduccia hypothesizes that birds originated from some mysterious Triassic ancestor, and then bird-like dinosaurs evolved from early birds, there is not a shred of evidence that such an evolutionary repeat ever took place. The idea is an attempt to remove uncomfortable facts in the way of a preconceived view.

Many of the book’s arguments take on a “because I said so” tone. Feduccia states that dinosaurs could not have been covered in protofeathers at any point because their archaic plumage would have gotten wet and mucky in the rain. Likewise, Feduccia argues that dinosaurs could not have evolved the long arms necessary for flight, and he casts dinosaurs as relatively sluggish ectotherms that had more in common with lizards and crocodiles than birds. None of these points are discussed in detail or backed up with sufficient evidence. Readers are left to take Feduccia at his word.

Ultimately, though, many of Feduccia’s objections boil down to a rejection of a methodology known as cladistics. This method of determining relationships among organisms is based on the analysis of shared derived characteristics—specialized features found in two organisms or lineages and their most recent common ancestor. Researchers look for numerous traits, record whether the traits in question are present or absent, and then insert that mass of data into a computer program that produces a hypothesis about the relationships among the various organisms included in the study. The point is not to find direct ancestors and descendants, but to figure out who is most closely related to whom. The method is not perfect—which organisms are included, the choice of traits for comparison and the way those traits are scored all affect the outcome. Still, this process has the benefit of requiring researchers to show their work. Each evolutionary tree resulting from such methods is a hypothesis that will be tested according to new evidence and analyses. If someone disagrees with a particular result, they can sift through the collected data to see if an inappropriate trait was included, an essential organism was left out, or if there was some other problem. Cladistics is useful not because it results in a perfect reflection of nature each time, but because it allows researchers to effectively examine, test and improve ideas about relationships.

Cladistic analyses have repeatedly found that birds are nested within a subgroup of coelurosaurian dinosaurs called maniraptorans. The result has only become more robust as additional archaic birds and non-avian feathered dinosaurs have been found. Feduccia argues that such results are deeply flawed, but he does not provide a viable alternative for how we should identify the relationship of birds to other organisms (an essential task if we are to figure out how birds originated). Categorizing organisms on general appearances, or making feathers synonymous with birds alone, will only confuse our understanding of prehistoric life. And, contrary to his protests, Feduccia seems to welcome cladistic results that support his own views. In a section of the book on the weird oviraptorosaurs, Feduccia plays up the importance of a 2002 paper that used a cladistic analysis to support the conclusion that these creatures were archaic, secondarily-flightless birds, even though additional studies have not supported this interpretation.

Riddle of the Feathered Dragons is an intensely frustrating read. The tome is a 290-page position piece that ultimately leaves the reader stranded. Feduccia is so concerned with turning feathered dinosaurs into birds that he ultimately neglects to present any reasonable hypothesis for where birds came from. The poor production of the volume only makes things worse (the illustrations are so tightly packed in places that they make it difficult to find where the captions end and the regular flow of the chapter picks up again.)

Although I wholly disagree with Feduccia, I had hoped that Riddle of the Feathered Dragons would explicate what opponents of the dinosaurian origin of birds believe about where avians came from. Simply repeating “birds are not dinosaurs” is not enough—positive evidence must play a role in forming an alternative hypothesis. The riddle of the “feathered dragons” is not where birds came from. The puzzle is why some scientists continue to insist that birds cannot be dinosaurs.