Another Strange Chinese Fossil Found: Dinosaur or Bird?
Feathers and wings are among the most distinguishing characteristics of birds. “Integumenary features” have been found on some dinosaur fossils, and true feathers have been found on some strange-looking extinct birds. The news media often try to marry the two into a committed relationship using exaggerated artwork. They have been found imagining feathers on fossils where the data are dubious or even missing (09/29/2008, 06/13/2007). What makes a structure a true feather? When does it support linking an unknown species into an evolutionary relationship to birds?
The latest case involves a strange fossil from China reported in Nature.1 Dated Middle to Late Jurassic in age, it is one of the earliest species to sport integumentary structures (see 10/06/2004, 10/12/2005), but it was nearly contemporary with early birds having true feathers. The media reports typically announce a “feathered dinosaur” has been found (e.g., BBC News “New feathered dinosaur discovered” and National Geographic “First Dinosaur Feathers for Show, Not for Flight?”) though some titles leave other interpretations open (e.g., Live Science, “Bird-Like Dinosaur Sported Bizarre Tail Feathers”).
Instead of allowing for the possibility that unrelated species had similarities, the articles often state matter-of-factly that birds evolved from dinosaurs. The BBC article was the most blatant in this regard, referring to the “critical transition from dinosaurs to birds” and quoting a paleontologist at London’s Natural History Museum stating, “It provides fascinating evidence of evolutionary experiments with feathers that were going on before small dinosaurs finally took to the air and became birds.”
The original paper did use the word feathers for the structures in the fossil of the new pigeon-sized creature from the Middle or Late Jurassic they named Epidexipteryx, but a closer look shows some findings that may not help the evolutionary scenario.
- None of the structures were pennate feathers, that is, with barbs and barbules from a central vane. The integumentary structures fell into two categories:
- “Shafted feathers” – Connected to the last ten tail vertebra were found two “membranous structures” consisting of parallel shafts that each branch once. Each shaft has a thin unbranched vane of material, like a coating, along a central rachis. The result appears as four long nearly-parallel rods that join at the base. Collectively they are nearly as long as the skeleton of the creature. Mark Norell (American Museum of Natural History) commented, “These seem to lack that main shaft down the middle and are just a really long collection of very long, filamentous-like structures.”
- “Non-shafted feathers” – These are rows of integument found outside the outline of skeleton, presumably from the skin. They all end in parallel rows of barbs, nothing like the cross-cutting structure of bird feathers; the BBC article calls it a “fluffy, down-like covering.” The authors stated, “the free distal barbs of Epidexipteryx arise from the edge of a membranous structure (Fig. 2b, c, d, d’), an arrangement that has never previously been reported.”
- Some of the structures bear similarities to those on Jeholornis, a creature interpreted as being capable of powered flight (see 07/24/2002).
- The authors allowed for the possibility that this creature was “secondarily flightless” – i.e., that it once had feathers like a bird, but lost them; if so, it was not evolving from a dinosaur into a bird.
- The authors suggested that the feathers on Epidexipteryx were used for display, not for flight, but the LiveScience article hypothesized they “likely helped the creature balance on tree branches.”
- The animal had a curious mosaic of traits. National Geographic remarked, “Epidexipteryx’s anatomy seems to be a hodgepodge of features taken from a variety of animals.” It seems to have been the “platypus” of the Jurassic – an improbable mixture of traits from different groups.
- Since the creature had a “surprising combination of physical features” (BBC News), it should not be envisioned as a transitional form from one lineage to another. The BBC News article complicated the evolutionary story by stating, “The discovery adds yet more complexity to the early history of the era when small meat-eating bipedal dinosaurs evolved into birds.” The evidence, therefore, makes the explanation more complex, not simpler, in contradiction to Occam’s Razor.
- The evolutionary date is too late to represent a pre-bird. The BBC article said, “whereas other feathered dinosaurs [sic] date from after the appearance of the first known bird, this fossil appears to be much closer in age, so it opens a new window on the evolutionary events at the critical transition from dinosaurs to birds.” Live Science says that the dates are uncertain; at best it was “slightly older” than Archaeopteryx. If it was nearly contemporaneous with a fully-feathered bird that was most likely capable of powered flight, it could not be a pre-bird, bird ancestor or missing link.
- The evolutionary link to birds is only inferential. Live Science quoted one of the authors saying, “Although this dinosaur cannot be the direct ancestor for birds, it is one of the dinosaurs that have the closest phylogenetic relationship to birds.”
- Mark Norell hinted that this fossil has more to say about diversity, not evolution. “Things more primitive than this have fully formed feathers” he said. “This is just some weirdo kind of thing this animal has.”
The Live Science article elaborated on Mark Norell’s comments about diversity within groups:
As scientists and others discover more and more dinosaur fossils with bird-like features, the picture of such creatures is becoming more complex, said Norell, who was not involved in the current study.
“Just like the bird diversity we have living today goes all the way from hummingbirds to ostriches to toucans, it’s incredibly diverse,” Norell said during a telephone interview. “Now we’re starting to see that sort of diversity extends not only in birds but also in the close bird relatives [which] were just as physically diverse as modern birds are.”
To infer evolutionary relationships, scientists conduct two kinds of studies. One is the cladistic study, that measures the number of specific characteristics in a fossil or creature, like the angle of its pelvic bone or ratio of skull length to skull width, and scores it in relation to other similar creatures. The other, when possible, is the genetic study of DNA similarities and differences. Assuming that common descent is true, they produce phylogenetic diagrams of ancestral relationships based on degree of similarity. Norell’s comments suggest that among a highly diverse set of organisms, the possibility of subjective inferences to ancestry is high – meaning that other inferences are legitimate, depending on which similarities are measured, and the relative weights assigned them by human minds.
1. Zhang et al, “A bizarre Jurassic maniraptoran from China with elongate ribbon-like feathers,” Nature 455, 1105-1108 (23 October 2008) | doi:10.1038/nature07447.
The artists’ renditions go far beyond the evidence: they’ve put vibrant colors on the alleged feathers and given the creature a whole life and personality. The structures cannot be called feathers except by stretching the definition of the term. The tail structures look like long rods. The “down-like coating” could be flayed skin, given that the creature was exceptionally well preserved. It may represent a mutant dodo-line of ancient birds that went extinct, or a member of a subclass of dinosaurs that shared the most similarities with birds without being related to them.
Scientists should be very careful about making inferences about any complex set of data. The bones do not jump up and announce that they were evolving into birds. The supplementary data in the paper show nearly 300 traits that had to be compared to make a cladistic analysis. The significance of any one of them requires a human judgment. Which traits are you going to focus on? Humans share traits with this fossil, too: vertebrae, teeth, radius and ulna, and many organs not visible from the bones. It is conceivable that the scientists in another civilization might consider size, habitat, lifestyle or some other characteristic to be the overriding concern in their way of classifying things. What kind of inferences would they draw? Complexity, diversity and “mosaics” of traits throw simplistic schemes into disarray. How would you rearrange your Evolutionary Tree of Tools if somebody handed you a Leatherman tool with a knife, screwdriver, pliers and scissors in a leather pouch?
Even granting, for the sake of argument, the most generous leeway to the evolutionists and calling the structures on this thing feathers does not help their story. Other feathered birds were nearly contemporaries. If this was an “evolutionary dead end,” where is the highway? A collection of dead ends may keep you busy, but is not going to get you anywhere.