March 12, 2008

100 Million Year Old Feathers Found in French Amber

100 million year old feathers in amber; photo from National GeographicSeven filamentous feathers have been found in amber thought to be approximately 100 million years old. The stratum in which this amber is preserved lies immediately above a layer from which teeth belonging to a theropod dinosaur that has been believed to be feathered based on previous specimens. It's worth noting that the fossils in this case post-date Archaeopteryx by about fifty million years, so these feathers probably aren't from the common ancestor of the dinosaur-bird lineage, but it is a distinct possibility that the organism in question is a direct descendant of the organisms that initially gave rise to that line. It is also possible that the feathers, while themselves rather simple, may represent a reduced form that was ancestrally more like the feathers we see in birds capable of flight. The feathers in this amber lack the structure necessary to support flight, but we also see feathers like them in modern flightless birds such as ostriches and emus. More investigation will be necessary to establish the identity and evolutionary position of the feathers. In any case, they provide evidence for the state of evolution at a relatively early point in the history of feathers and may well turn out to be the best-preserved examples of feathers from a theropod to date.

Dino-Era Feathers Found Encased in Amber

Seven dino-era feathers found perfectly preserved in amber in western France highlight a crucial stage in feather evolution, scientists report.

The hundred-million-year-old plumage has features of both feather-like fibers found with some two-legged dinosaurs known as theropods and of modern bird feathers, the researchers said.

This means the fossils could fill a key gap in the puzzle of how dinosaurs gave rise to birds, according to a team led by Vincent Perrichot of the University of Kansas's Paleontological Institute.

The find provides a clear example "of the passage between primitive filamentous down and a modern feather," said team member Didier Néraudeau of the University of Rennes in France.

The study team isn't sure yet whether the feathers belonged to a dino or a bird.

But fossil teeth from two dino families thought to have been feathered were excavated from rocks just above the layer that contained the amber, Perrichot said...

Perrichot found the tiny feathers encased in a lump of amber, a fossilized tree resin, in a quarry in the Poitou-Charentes region of France in 2000.

The feathers' central shafts, or rachis, are primitive and most closely resemble down feathers, the study team noted.

The feather filaments, or barbs, had yet to become fully fused at the base and—like modern down—they lacked hooklets known as barbules to hold the filaments together.

Studies suggest primitive feathers first evolved in flightless dinosaurs that generated heat internally and so would have benefited from the insulation that down can provide...

"This most critical step in the evolution of feathers" was suggested by evolutionary theories but had never previously been seen in either modern or fossil feathers, he said.

Team member Néraudeau added that this missing link has been "an argument for creationists and others to reject the theropod-birds lineage and to argue in favor of different origins for theropod feathers and bird feathers.".."

The bird-fossil expert, who was not involved in the study, noted that the newfound feathers are around 50 million years younger than the first known flying bird, Archaeopteryx, which lived about 150 million years ago.

"Obviously this animal [the feathers came from] isn't directly ancestral to anything except later dinosaurs, but it's quite likely that we are seeing aspects of the ancestral [feather structure]," Longrich said in an email...
Coincidentally, I taught a lesson in phylogeny and building trees to my lab class yesterday. To help illustrate the point of how phenotypic characters can be used in tree construction, I showed them some intermediate creatures that could be used (for the purposes of a simple lesson in phylogeny, anyhow) to illustrate what the ancestor at a node might look like. Among these were Tiktaalik, Basilosaurus and, of course, Archaeopteryx. I spent a bit more time on Archaeopteryx because most students are more familiar with birds than amphibians or whales and it was easy to point out the combination of avian and reptilian characters in that organism in a way that students can grasp easily. Everyone knows that birds don't have teeth (except for the ephemeral egg-tooth in some species) and clawed forelimbs (except for the ephemeral claws found on Hoatzin chicks). While I did make sure they understood that Archaeopteryx itself can't be definitively assigned as an ancestor/node leading to modern birds, we can say that it is much more like that ancestor than any of the birds or reptiles we see in the world today and, if not the node itself, at least represents a taxon relatively close to that node. The same could be said for the amphibian and whale "ancestors" used as examples.

About half the students had never heard of Archaeopteryx and not a single one had heard before of Tiktaalik or Basilosaurus. This is the situation among students who all took biology classes in Massachusetts high schools, save for one transplanted Rhode Islander. If this is the situation here, where we are said to have one of the best science education programs of any state in the country, it isn't too hard to puzzle out why there are still people in places like Florida and Alabama, which have not had strong science education programs to date, who can go about believing that there are no "transitional" fossils and hence no evidence for evolutionary processes through time. Those are the ones, generally, who will assert that there's no evidence for macroevolution because they don't see any "half-fish, half-human" fossils.

I think that when my lab section next meets, I'm going to show them the National Geographic photo above and talk a little bit about this recent find. It's pretty cool stuff and I think most of them will find it more interesting than the ensuing lab exercises on single-celled organisms.

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