“Dinosaur feathers” are all over the news again, thanks to a paper in Science revealing feathers in amber found in Canada. But whose feathers are they? Inferences from other sources, not from the amber, were brought into the interpretation, even though the discoverers admitted, “There is currently no way to refer the feathers in amber with certainty to either birds or the rare small theropods from the area.” And modern-looking feathers of diving birds like grebes were also found in the same amber, leading to numerous questions about what can rightly be inferred from the fossils themselves. No matter; most of the media loved the evolutionary implications and trotted out their headlines that feather evolution from dinosaur to bird has been proven.
McKeller, Chatterton, Wolfe and Currie combed through 4000 amber samples in two Canadian museums taken from around Grassy Lake, Alberta. The strata are said to be late Cretaceous and dated at 80 million years old, way into the period in the evolutionary timeline when birds already were flying like modern birds. The amber samples were already well known for their diverse insect inclusions, but for the first time, feathers were found, in a variety of forms.
“Although amber offers unparalleled preservation of feathers, only isolated specimens of uncertain affinity have been reported from the Late Cretaceous,” the authors began their paper in Science.1 “This contrasts with the rich Early Cretaceous compression assemblage from northeastern China leaving a substantial temporal gap in our understanding of feather evolution,” to say nothing of a geographical gap (the only other alleged dinosaur-to-bird “transitional form” being Archaeopteryx from Germany – but see 7/21/2011 and PhysOrg reinterpretation and new questions). Considering these two substantial gaps, how could the authors claim they were watching feather evolution in action, from dinosaur to bird?
For one thing, they found a variety of feathers and feather parts that they fit into the “currently accepted evolutionary-developmental model for feathers.” Evolution was, therefore, assumed from the outset. They found single filaments (stage I in the model), tufts (stage II), simple feathers (stage III), barbed feathers (stage IV), and advanced veined feathers (stage V) suitable for flight or for diving (as found in grebes). It didn’t bother them that all of these stages can also be found on modern birds, or can represent degenerate structures from modern feathers in fossils.
For another thing, “Although neither avian nor dinosaurian skeletal material has been found in direct association with amber at the Grassy Lake locality, fossils of both groups are present in adjacent stratigraphic units,” they said. “Hadrosaur footprints are found in close association with the amber, and younger (late Campanian and Maastrichtian) strata of western Canada contain diverse nonavian dinosaur and avian remains.” By interpretation, they meant plain old dinosaurs (nonavian) and plain old birds (avian). None of these feathers were found on dinosaurs, and no one doubts that dinosaurs and birds coexisted; the question is whether dinosaurs evolved into birds. Despite these questions, they gunned the inference engine:
There is currently no way to refer the feathers in amber with certainty to either birds or the rare small theropods from the area. However, the discovery of end-members of the evolutionary-developmental spectrum in this time interval, and the overlap with structures found only in nonavian dinosaur compression fossils, strongly suggests that the protofeathers described here are from dinosaurs and not birds. Given that stage I filaments were present in densities relevant for thermoregulation and protection, and that comparable structures are preserved as coronae surrounding compression fossils, it becomes apparent that protofeathers had important nonornamental functions. Specialized barbule morphologies, including basal coiling, suggest that Campanian feather-bearers had already evolved highly specialized structures similar to those of modern grebes to enhance diving efficiency.
This remarkable paragraph indicates that they were already assuming that simple filaments and tufts were protofeathers; i.e., dinosaur integumentary structures evolving into true feathers. The prefix “proto-” turns on the power of suggestion that these structures were evolving upward instead of devolving downward. It also reveals that they were assuming that feathers first evolved on dinosaurs for “nonornamental functions” such as thermoregulation – yet many modern birds, like geese, also use some of their feathers (down feathers) for thermoregulation. Moreover, the pieces of amber could not show where on the body of any animal, whether bird or dinosaur, they came from. Clearly these authors were eager to fit their data into a dinosaur-to-bird sequence. But since these feathers appear so late in the geologic column, the most that can be claimed by believers in dinosaur-to-bird evolution from these amber pieces is that early primitive dinosaur feathers, if they existed, hung on for a long time, even after modern flight feathers had already evolved.
Nevertheless, Mark Norell in the same issue of Science was ecstatic.2 Co-author of an annual review on feather evolution with famous Chinese “feathered dinosaur” hunter Xing Xu, he bragged about all the fossil evidence birds evolved from dinosaurs, and said, “Feathered animals abound and extend deep into nonavian history—even, perhaps, to the base of dinosaurs themselves.” The press flew into a frenzy, with the BBC News leading the flap with its headline, “Dinosaur feather evolution trapped in Canadian amber.” Science Daily flew into formation with, “Tree Resin Captures Evolution of Feathers On Dinosaurs and Birds.”New Scientist showed a little more scientific restraint in its headline (but not in the body of the article) with, “Advanced birds lived alongside 'hairy' dinosaurs.”
Only Live Science took “a closer look” at the data and asked other paleontologists for alternative interpretations:
The fossil record of this evolution from simple to complex feathers is spotty. Researchers actually have older records of more modern feathers than they do of the simple dinosaur protofeathers....
[Zhonghe] Zhou [Chinese Academy of Sciences] also noted that some of the feathers were more difficult to classify based on type, so scientists can’t really be sure if they are bird or dinosaur feathers, or somewhere in between. Mike Benton of the University of Bristol had the same reservations.
"Modern feathers are diverse in morphology," Benton told LiveScience in an email. “Many degenerated [feathers that have turned back the evolutionary clock and become more simplified] or specialized feathers are comparable in morphology to the protofeathers.”
This means that the so-called protofeathers could have been bird feathers devolving into simpler structures, rather than being dinosaur structures evolving into bird feathers. The authors of the paper added two other caveats:
All they could offer, therefore, was a “snapshot” – not an evolutionary sequence – of a few feather types that were around a particular lake at a particular time in Canada. But they were certain that, “Despite these limitations, the assemblage demonstrates that numerous evolutionary stages were present in the Late Cretaceous, and that plumage already served a range of functions in both dinosaurs and birds.” Did the amber really say that?
Source: Creation-Evolution Headlines