What Is the Evidence for Feathers Before Flight?
Birds evolved from dinosaurs; that’s the evolutionary consensus. Let’s examine the evidence for that scenario.
In “Feathers Before Flight,” Julia Clarke [U of Texas] gathered together the evidence birds evolved from dinosaurs in a Review article for Science Magazine. To the untrained eye, the confident assertions can seem convincing. Buried within the text, though, are the bits and pieces of actual fossil evidence used to support the conclusion. Do they support the evolutionary picture? Her first paragraph seems to have more gap than link:
Feathers are branched structures consisting of β-keratin—a rigid protein material formed by pleated β sheets—with a hollow central shaft. They are strikingly different from other forms of vertebrate integument such as scales, skin, and hair. Until recently, evolutionary hypotheses envisioned their origin through elongation of broad, flat scales driven by selection for aerial locomotion such as gliding or flapping flight. Over the course of the past two decades, fossil discoveries, especially from northeast China, have revealed that the early precursors of feathers were filament-like rather than expanded scales and that branched pinnate feathers of modern aspect predate the origin of active flight. The revolution in our understanding of feather evolution continues, driven by rapid fossil discoveries and by new information from the study of extant birds.
She implies that the scale-to-feather theory is out. Somehow, filaments emerged where scales once existed. Two statements stand out in this quote: that feathers are “strikingly different from any other forms of vertebrate integument,” and that “branched pinnate feathers predate the origin of active flight.” The first is confirmed by discussions in the new Illustra Media documentary Flight: The Genius of Birds, where an animation of a single feather shows a complex structure complete with a hook-and-groove microstructure that provides an ideal mechanism for flight: lightweight, flexible, and strong. The second claim, that feathers predate flight, will have to be supported further down in Clarke’s review.
Clarke calls the new ideas of feather evolution “transformative,” suggesting that previous evolutionary scenarios taught in textbooks are no longer correct. Most notable in transforming evolutionary beliefs have been the Chinese fossils:
The Chinese deposits provide one such unique snapshot, where over a thousand specimens with fine details of soft tissues such as feathers, hair, and skin are preserved in ash-rich lake deposits ranging from the Late Jurassic (∼150 million years ago) to the Early Cretaceous (∼120 million years ago). Fossils from these deposits have revealed that dinosaurs that were inferred from bone characteristics to be closely related to living birds also share more features of feather structure.
Acceptance of the evolutionary story is going to require acceptance of the dates, and with that, the belief that a lake was repeatedly buried in ash over a period of 30 million years – a very long time for an ecological community to survive with volcanoes going off. Has anyone thought that through? Would a dinosaur with filaments get buried in ash, then a lake form again, then more-evolved creatures with more-advanced feathers happen along, only to be buried in fine ash again, preserving soft tissues? Would this cycle repeat for 30 million years?
Between Clarke’s retellings of the consensus dinosaur-to-bird scenario, curious statements appear. “The latter forms do not fit the hypothesis of flat scales morphing directly into flat feathers,” she writes. “But these hollow filaments or ‘protofeathers’ are similar to structures seen early in feather development; a simple hollow cylindrical sheath arises first in feather ontogeny from the collar of the feather follicle before the barb ridges, linked to the development of its branching shape, form.” There are two problems for evolution here. One is the gap between scales and filaments. The other is that her statement sounds like Recapitulation Theory: a modern bird’s feathers remember their ancestral forms as they develop. The idea that “ontogeny recapitulates phylogeny” is generally frowned upon in evolutionary circles.
Another problem is her statement, “Fossil data indicated dramatic shifts from scale to filament, to bunches of filaments, to branched feathers in theropod dinosaurs.” Evolutionists typically like to avoid dramatic shifts, preferring gradual changes that mutation and selection can accommodate. (Whether theropod dinosaurs had branched feathers will have to wait for the fossils she presents.)
But then, Clarke mentions another gigantic conundrum confronting the simple scenario:
The more recent discoveries of a basal ornithischian dinosaur with a filamentous body covering, and another ornithischian more closely related to Triceratops with a bristle-covered tail, force reconsideration of the timing of this transition. These fossils indicate that filamentous structures may be ancestral to dinosaurs. Filaments called pycnofibers also covered some pterosaurs. Ornithischian dinosaurs, sauropod dinosaurs, and pterosaurs are on evolutionary branches that split from that of theropod dinosaurs and birds about 230 million years ago in the Triassic. If these structures have the same evolutionary origin, a form of filamentous integumentary structure evolved from scales nearly 100 million years before the locomotor transition that we call the origin of birds (see the figure).
If 30 million years is a problem, how about 100 million? The findings (accepting the evolutionary dates) now require filaments to evolve from scales way back, 230 million years ago, long before Triceratops, T. Rex and pterosaurs (let alone feathered theropods) – only to come and go in various species for 80 to 100 million years. Is that plausible? And why would feathers “evolve” out of scales long before any functional adaptation?
The figure Clarke referred to should be fodder for creationists. It shows true pinnate feathers and simple filaments emerging virtually simultaneously in different branches, long after the split from Archosauria. Not only does this show abrupt appearance; it shows no ancestral relationship between the filaments and the true feathers. What’s more, the feathers are used for flight in some of the creatures suddenly at the earliest appearance of any integumentary structures. Instant birds! If her diagram is authoritative for the evolutionary story, it has “evolution of filaments” a good 50 million years before the first fossil bearing those filaments or feathers – simply because the timing of presumed evolutionary splits between various groups requires the filaments to be in the common ancestor. Apparently, it is too difficult a pill to swallow for “convergent evolution” of these structures.
The emerging evolutionary story is far from simple. Clarke points out important questions it raises:
The recent fossil data suggest that key integumentary shifts might be related not to flight but to innovation in stance, terrestrial gaits, and life history in early archosaurs, which came to dominate terrestrial ecosystems by the end of the Triassic. However, there are unanswered questions. Were there at least three independent and convergent shifts from scales to filaments in Archosauria, with only one of these linked to the origin of feathers and flight? Or was there a single ancient origin of filaments, with subsequent losses in some species and, much later, a second period of novelty seen in the evolution of a branching feather form? Answering these questions is key to understanding the evolution of feathers and other integuments.
That these key questions remain unanswered undermines simplistic portrayals that “birds are dinosaurs.” Generally, composite explanations are not useful in science. Clarke says that “key integumentary shifts might be related not to flight but to innovation in stance, terrestrial gaits, and life history in early archosaurs….” Well, which is it? Composite explanations won’t do for the student who excuses his missing homework with “either the dog ate it, or my sister threw it away, or I forgot it was due.” Science needs definitive explanations. Besides, abrupt appearance is the norm throughout this story. What is a “key integumentary shift,” anyway? Did it just “happen” somehow? What is “innovation,” or a “single ancient origin,” or a “period of novelty” but a confession of ignorance of any mechanism to explain how it arose? Where are the fossils? The figure caption reads, “Filamentous feather precursors may have originated nearly 100 million years before the origin of flight, but very few fossil deposits sample this period.”
So despite the confidence shown on TV and museum displays, the critical fossil evidence for the origin of flight is missing.
These questions send paleontologists back into the field. Early fossils of most major archosaur lineages are known from records in the Late Triassic and Early to Middle Jurassic (∼225 to 165 million years ago). However, no dinosaur older than the Late Jurassic has been recovered with preserved integuments (scales or feathers). Early pterosaurs are virtually unknown in the fossil record; their earliest fossils with integuments are also Late Jurassic in age (see the figure). A Late Triassic or Early Jurassic site with fine-scale soft tissue preservation would offer crucial insight into this question. However, very few candidate sites are known.
Clarke becomes more confident again, if the early evolution can be ignored. “The fossil snapshots that we do have offer much more insight into the evolution of pinnate feathers seen in living birds,” she says, launching into a discussion of what feathers might have been used for before flight emerged. Maybe it was for sexual display. “There is no known analog of archosaur filaments in adult living animals, but bird feathers are known to have diverse functions, for example, in flight, display, camouflage, and heat retention.” Feathers on modern birds might be used for sexual selection, she notes. But she’s talking about “living birds” there, not where they came from. It’s only inference that dinosaurs used them for sexual selection before they thought of taking to the skies. How did that happen? It’s time to get specific about the origin of flight. Remember as you read her statement that living birds are irrelevant. Where are the fossils?
Evidence is thus accruing for the function of early pinnate feathers in sexual selection, but there is little consensus on shifts in feather function associated with the evolution of flight. Reconstruction of ancestral conditions for the bird lineage requires consensus on the evolutionary relationships of key species. These species differ in feather shape as well as in their organization and layering on the forelimb and hind limb. Whether observed differences can presently speak to a gliding or flapping origin for flight is debated. Species with elongate feathers or a “wing” on the hind limb show characters consistent with a form of aerial locomotion but not one seen in living birds. At the same time, continued research indicates a broader variety of locomotor functions for forelimb feathering in living birds other than powered flight; young living birds flap short pinnate feathers on the forelimb, increasing traction to climb highly inclined surfaces. Although historically, feathers were firmly linked to flapping flight, the evolution of their early locomotor function in climbing, taking off, turning, landing, gliding, or flapping is a key outstanding question.
The reference to “young living birds” on “inclined surfaces” is a hat tip to Ken Dial’s “WAIR” hypothesis (wing-assisted incline running), in which he watched living partridge chicks raising their forelimbs as they scuttled up ramps (see story and comments from 12/22/03, 12/03/12). Her final paragraph is basically an admission that there are more questions than answers about the origin of flight:
The evolution of feathers is now seen as one part of a broader story concerning the origin of novel integumentary structures in archosaurs, although data on the early parts of this story are very limited. New data multiply the set of questions we must ask about the locomotor transition that we call the evolution of flight. Model-based approaches are needed to explore the varieties of aerial and nonaerial locomotor strategies that extinct dinosaurs may have employed. These must take into account not only the diverse locomotor strategies in living birds but also potential differences in feather properties, shape, and plumage organization.
Like Illustra’s film on Flight says about current speculations on the evolution of flight, “Each of these theories is highly controversial.” The film contends that the functional requirements for powered flight cannot be achieved piecemeal by gradual steps. “It’s really an all-or-nothing proposition,” Paul Nelson explains; “You don’t partly fly, because flight requires not just having a pair of wings, but having your entire biology coordinated towards that function.” Even if dinosaurs were capable of employing “nonaerial locomotor strategies” of some undefined nature, how did a “locomotor transition” occur, leading to all the biological “innovations” required for powered flight?
Clarke began with a promising title, “Feathers Before Flight.” She ended on a series of unanswered questions – primarily, “New data multiply the set of questions we must ask about the locomotor transition that we call the evolution of flight.”
Oh, wow, this article is so classic of the evolutionary genre, it’s a virtual gift to creationists. Aside from the obvious evidential conclusion that dinosaur-to-bird evolution is a myth, Clarke used all the evolutionary tricks of the trade we’ve been pointing out in the Darwin lit for 12 years now: the Stuff Happens law, just-so stories, shielding complex changes in words like “novelty” and “innovation,” promissory notes, the coulda-woulda-shoulda habit, embedding evolution in terms like “protofeathers,” the convergence concoction, using passive verbs and subjunctive mood as covers for ignorance, composite explanations, punk eek, incredible stasis, ghost lineages, “more research is needed,” job security for storytellers, glossing over soft tissue in supposedly ancient material, tidbits of Lamarck and Haeckel as needed when gradualism doesn’t work, forcing uncooperative data into prefab scenarios, parading naked Emperor Charlie in public, sacrificing brains at his shrine – everything. Hardly a sentence of this article is devoid of fallacies masquerading as science.
We hope you caught these things before the commentary began. If not, you need Creation-Evolution Headlines as a deprogramming course. Bookmark this site and come for your daily therapy. Since Ken Dial made an off-camera appearance, we like all beginners to get the shock treatment in our commentary from 12/22/03 – the first time (now a decade ago, still cited favorably by Darwinists) the Montana drunkard-on-Darwine presented living partridge family chicks as possible props to an evolutionary tale. Read that color commentary now; know the tricks, and you won’t be fooled again.