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.
It is ridiculous for birds and mammals. We said nothing of other clades.
If you define those "forces" as agents which limit viability, you just said what I said. If you suggest forces that DON'T limit viability, but somehow otherwise conveniently limit mutations that should occur and would be viable simply so we don't have a huge variability, I'm not sure what the point OR the mechanism would be.
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.
THank you.
That's probably why Inuit have darker skin to absorb UV energy than say - the Zulu. O wait,...never mind.
Nevermind indeed.
Look, the point is: you guys make such matter-of-fact assertions regarding environmental factors effecting changes in populations but you have no ability to predict which factors effect which changes.
All you can do is look backward and say "whatever has changed is evolution". What friggin' value is there in that?
...and by the way, why is it so out of the realm of possibility that in another gabillion years the Inuit will indeed have evolved features very different from humans in other climates?
My only point is that skin color is obviously adaptive, regardless of the cause. You have the adaptive value of color backwards, regardless of you position on evolution.
From the equator to the north skin color lightens to absorb more UV for production of vitamin D. The counter factor is keeping the level of UV low to avoid skin cancers. When you get too far north, no amount of skin lightening will work, so people only went farther north when they were able to supplement their diets.
In the extreme north, diets must be supplemented with vitamin D, and no amount of skin exposure would produce appreciable amounts of vitamin D before freezing set in. People there supplement their diets and wear cloths, so there is no longer selection pressure for very light skin. Sking color is generally about the world average.
On what basis do you make this statement?
Check out post 169.
Yeah, two typos in post 169. That's what comes of posting while talking on the phone.
cloths = clothes
Sking = skin
Duh!
How many of them are vertebrates? Better yet, how many vertebrates are headless?
I'm working on a line of reasoning that will work for either example, however, I'll have to ponder it a bit, so - I'm just gonna take it on into the weekend and sign off for now.
Take it easy fellas.
"The very reason such checks as peer review are built into science is because scientists do recognized their own fallibility and tendencies to bias."
There are many examples which have been pointed out on these threads which go against your statement. From global warming and medical research come the most spectacular examples of people who have peer reviewed studies which are designed to show an outcome which the researcher desires.
IMHO I think the general public turns a very skeptic eye toward the supposed unbiased reasearch from today's science community.
I saw this in the paper and I was doing real great until I saw that it was about the size of a robin and the whole picture collapsed.
I'm working on a line of reasoning that will work for either example, however, I'll have to ponder it a bit
If you are working on IR it is something I have never seen addressed in human races studies. Keep me informed of what you find. It could be interesting!
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