Posted on 06/15/2006 11:39:26 AM PDT by PatrickHenry
Five fossil specimens of a near-modern bird found in the Gansu Province of northwestern China show that early birds likely evolved in an aquatic environment, according to a study reported today in the journal Science. Their findings suggest that these early modern birds were much like the ducks or loons found today. Gansus yumenesis, which lived some 105 to 115 million years ago during the Early Cretaceous period, took modern birds through a watery path out of the dinosaur lineage.
The report was co-authored by Peter Dodson of the University of Pennsylvania and his former students Hai-lu You of the Chinese Academy of Geological Sciences, Jerald Harris of Dixie State College of Utah and Matthew Lamanna of Carnegie Natural History Museum in Pittsburgh.
"Gansus is very close to a modern bird and helps fill in the big gap between clearly non-modern birds and the explosion of early birds that marked the Cretaceous period, the final era of the Dinosaur Age," said Peter Dodson, professor of anatomy at Penns School of Veterinary Medicine and professor in Penns Department of Earth and Environmental Sciences. "Gansus is the oldest example of the nearly modern birds that branched off of the trunk of the family tree that began with the famous proto-bird Archaeopteryx."
Gansus yumenensis takes its name from the Gansu region, where it was found, and the nearby city of Yumen. According to Dodson, Gansus is something of a lost species, originally described from a fossil leg found in 1983, but since largely ignored by science. The five specimens described by Dodson and his colleagues had many of the anatomical traits of modern birds, including feathers, bone structure and webbed feet, although every specimen lacked a skull.
"It appears that the early ancestors of modern birds lived lifestyles that today we would stereotype as being duck-like, heron-like, stork-like, loon-like, etc.," said Jerald Harris, director of paleontology at Dixie Sate College of Utah. "Gansus likely behaved much like its modern relatives, probably eating fish, insects and the occasional plan. We won't have a definitive dietary answer until we find a skull."
The skeletons, headless as they are, offer plenty of evidence for a life on the water. Its upper body structure offers evidence that Gansus could take flight from the water, like a modern duck, and the webbed feet and bony knees are clear signs that Gansus swam.
"Webbed feet is an adaptation that has evolved repeatedly in widely separate groups of animals, such as sea turtles, whales and manatees, and would only hinder climbing or landing in trees," Harris said. "The big bony crest that sticks off the knee-end of their lower leg bones are similar to structures seen in loons and grebes. These crests anchor powerful muscles needed for diving under water and swimming."
According to Harris, these adaptations all demonstrate how the Gansus branch of the family tree, the structurally modern birds called ornithuromorphs, split from the enantiornitheans (or "opposite birds"). Enantiornitheans were among the feathered fossils found in northeastern China during the 1990s.
"The enantiornitheans had the best adaptations for perching, so they were able to dominate the ecological niche that we would associate with songbirds, cuckoos, woodpeckers or birds of prey," Harris said. "Gansus appears to have had adaptations for a lifestyle centered around water, based on things like the proportions of the leg and foot bones."
While the enantiornitheans are now long gone, their perching lifestyle has now been taken over by the descendents of birds like Gansus. What remains a mystery for now, according to the researchers, is how the amphibious lifestyle of birds like Gansus helped enable them to survive the cataclysmic end of the dinosaurs 65 million years ago.
Funding was provided by the Discovery Channel (Quest program) and the Science Channel, the Carnegie Museum of Natural History, Dixie State College, the Chinese Geological Survey of the Ministry of Land and Resources of China and the Gansu Bureau of Geology and Mineral Resources.
Although it is silly to call the many forms of selection 'forces', calling them that does simply the language when discussing them.
Organisms tend to cluster around the point of optimum fitness given normal morphological and environmental constraints simply because it is more likely for a specific mutation to be neutral and not contribute immediately to fitness, or deleterious and quickly removed, than they are to be immediately beneficial. But yes, relative viability is the mechanism that limits variability. However, the contribution a mutation makes to viability is dependent on the environment and a change in environment can change which mutation (which is the source for new alleles) fixes in a population.
"Put another way, I see neither the point nor the operability of selection forces that don't effect viability or opportunity to succeed but still manage to prevent mutations that have occured from spreading in the population. I guess that seems like the definition of viability and opportunity -- at least that's what I was trying to cover with those terms, which I admit may not be the scientific technical terms for whatever processes you envision.
Random drift can control the frequency of an allele without viability having anything to do with it but deleterious mutations don't usually last long enough to be affected.
Haven't seen Mr Ducks for a long time!
Thanks for posting. I still have the t-shirt somewhere.
As Martin Gardner pointed out in "Fads and Fallacies in the Name of Science" over forty years ago, one can dismiss the entire fossil record, carbon-14 and all other evidence of evolution by invoking an omnipotent creator. Either life on Earth has evolved over a period of hundreds of millions of years, through changes in climate and geology, or God made a world a few thousands years ago with attributes completely consistent with the former hypothesis.
Which of the two theories you prefer probably says more about you than the validity of either theory.
Only if you assume that a single form of selection can affect skin colour.
Only if you assume that the sun is the only way to acquire vitamin D.
Only if you ignore the cause of "skier's tan".
"how many vertebrates are headless" is the same as "how many headless are vertebrates"
Maybe you meant "what percentage of" -- that could be different because of the different populations.
Of course, we all know that there are no headless vertebrates. In fact, if we were told a life form was headless, we would assert that it wasn't a vertebrate, and if someone showed us bones that suggested it WAS a vertebrate, but assured us there was no head, we would assume either the bones did not go together the way we thought, or the person was wrong about there not being heads.
I'm still hung up on creatures evolving from the sea to the land but then evolving back into the sea. That would seem odd until we found evidence of it, but then it must be accepted because it is observed.
If we ever FOUND a headless vertebrate, we would have to re-think our assumptions, I guess, not that I think we'll ever find such a creature. I've never met a creature who used to have a head and now doesn't but is still alive.
Of course, I've never met a creature with a half-formed head either, but I presume we must believe they existed at some point since we obviously didn't evolve an entire head with a single mutation (if we did, then one could postulate a single mutation that would reverse the process).
Oddly, we evolved a tail, and then managed to evolve it away, so it's not like we don't have evolutionary examples of body parts coming and going.
But not, I repeat again, a head. Because as I said a hundred posts ago, asking about the missing heads was a way of focusing on an issue by using an obvious example, and was in no way construable as saying that the birds in the example didn't have heads.
But it was much easier to argue that they must have had heads and it was stupid to suggest otherwise (now THAT was a strawman argument) than it was to discuss the issue of seeing what you expected to see.
That is true, the construct was overly broad (too simplistic I would argue) -- my point wasn't really about infinite possibilities so I didn't think of it that way until you mentioned it.
"PROTIP: Instead of merely stating that examples exist, you should present specific cases to your reader."
Anyone on these threads for any lenth of time knows that this has been roundly discussed, besides the fact that anyone who keeps up with current events has seen this stuff in the news as well.
A poor excuse. Such an attitude is a disservice to your reader.
It was only a recommendation. You wish your arguments to remain unremarkable. Who am I to stop you?
"Who am I to stop you?"
I wasn't asking for your opinion anyway.
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