Posted on 07/03/2006 12:32:51 PM PDT by Al Simmons
In the 1993 movie Jurassic Park, one human character tells another that a Tyrannosaurus rex can't see them if they don't move, even though the beast is right in front of them. Now, a scientist reports that T. rex had some of the best vision in animal history. This sensory prowess strengthens arguments for T. rex's role as predator instead of scavenger.
Scientists had some evidence from measurements of T. rex skulls that the animal could see well. Recently, Kent A. Stevens of the University of Oregon in Eugene went further.
He used facial models of seven types of dinosaurs to reconstruct their binocular range, the area viewed simultaneously by both eyes. The wider an animal's binocular range, the better its depth perception and capacity to distinguish objectseven those that are motionless or camouflaged.
T. rex had a binocular range of 55, which is wider than that of modern hawks, Stevens reports in the summer Journal of Vertebrate Paleontology. Moreover, over the millennia, T. rex evolved features that improved its vision: Its snout grew lower and narrower, cheek grooves cleared its sight lines, and its eyeballs enlarged. ...
Stevens also considered visual acuity and limiting far pointthe greatest distance at which objects remain distinct. For these vision tests, he took the known optics of reptiles and birds, ranging from the poor-sighted crocodile to the exceptional eagle, and adjusted them to see how they would perform inside an eye as large as that of T. rex. "With the size of its eyeballs, it couldn't help but have excellent vision," Stevens says.
He found that T. rex might have had visual acuity as much as 13 times that of people. By comparison, an eagle's acuity is 3.6 times that of a person.
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T. rex might also have had a limiting far point of 6 kilometers, compared with the human far point of 1.6 km. These are best-case estimates, Stevens says, but even toward the cautious end of the scale, T. rex still displays better vision than what's needed for scavenging.
The vision argument takes the scavenger-versus-predator debate in a new direction. The debate had focused on whether T. rex's legs and teeth made it better suited for either lifestyle.
Stevens notes that visual ranges in hunting birds and snapping turtles typically are 20 wider than those in grain-eating birds and herbivorous turtles.
In modern animals, predators have better binocular vision than scavengers do, agrees Thomas R. Holtz Jr. of the University of Maryland at College Park. Binocular vision "almost certainly was a predatory adaptation," he says.
But a scavenging T. rex could have inherited its vision from predatory ancestors, says Jack Horner, curator of paleontology at the Museum of the Rockies in Bozeman, Mont. "It isn't a characteristic that was likely to hinder the scavenging abilities of T. rex and therefore wasn't selected out of the population," Horner says.
Stevens says the unconvincing scene in Jurassic Park inspired him to examine T. rex's vision because, with its "very sophisticated visual apparatus," the dinosaur couldn't possibly miss people so close by. Sight aside, says Stevens, "if you're sweating in fear 1 inch from the nostrils of the T. rex, it would figure out you were there anyway."
Stevens, K.A. 2006. Binocular vision in theropod dinosaurs. Journal of Vertebrate Paleontology 26(June):321-330.
"Selection pressures don't have to exist (e.g. in a zoo)."
Selection pressures do exist in a zoo.
"Mutations can happen without selection pressures (e.g. in a lab that is creating pigs to produce human growth hormone)."
Those mutations get selected for by the lab researcher. Selection can't be eliminated.
"Which is to say, my examples can't be logical fallacies. Fallacies don't happen. My examples do."
No, they really don't.
"No, they can't. Selection is ALWAYS present. You cannot get rid of it, no matter how much you try. Selection doesn't have to select for change."
Incorrect. Selection pressures do not have to exist, say, in a zoo...which is why *some* endangered species can survive in captivity that can't survive in the wild.
Ditto for a lab.
"Incorrect. Selection pressures do not have to exist, say, in a zoo...which is why *some* endangered species can survive in captivity that can't survive in the wild."
All that means is that the selection pressures are DIFERENT, not that they don't exist.
Straw man rubbish.
The alligators alive today would appear virtually identical to the alligators of 20 million years ago.
Must I point out that the above axiom stands apart from any speciation events during the same period of time?! Don't play dumb.
Your link in 151 says nothing about the evolution of aligators.
"No, they really don't."
Yes, labs really can eliminate selection pressure. So can zoos. Yes, labs and zoos really exist.
On the other hand, there isn't anything left of your poor argument. Too bad.
It says that they haven't really changed. If that doesn't tell you something about their "evolution," then you are on the wrong thread.
You lie!
Show me ONE PLACE I said "no mutation." Just ONE.
I proved your statement wrong. (Post #298: "The random mutation rate over vast amounts of time must roughly correspond to the changes seen in any given species (for Evolutionary Theory to have a snowball's chance of being correct, anyway).") I never said anything about "no" mutation... all of my statements have been about the ratio you posited. Your ratio fails because you attempt to claim something that no one has suggested. No one has said that speciation would occur with no mutations...mainly because it is impossible to have zero mutations in a large population. Just because at zero mutations might have a high influence on change does not mean that everywhere else on the graph of mutation vs. selection that it does so. Obviously all graphs must be straight lines? (linear thinking can be added to binary thinking on your list of fallacies...)
Stop creating straw men, and argue the statement you made. You asserted the graph of mutation rate vs. evolutionary change must be roughly an ascending line. Now prove it!
"Mutations can happen without selection pressures (e.g. in a lab that is creating pigs to produce human growth hormone). "
Selection pressures are heightened in the lab setting. How do you think they get the right mutation?
"Yes, labs really can eliminate selection pressure. So can zoos. "
No they can't. They just change it to select for something else.
Keep flailing away.
What?! No selection pressure in a zoo? No animal is exposed to other than normal behaviors or normal environments in a zoo? Wide-ranging animals, highly territorial animals, stress-sensitive animals don't face selection pressures in zoos? What planet do you live on?
"No they can't. They just change it to select for something else."
You're reduced once again to arguing semantics. Labs and zoos can eliminate selection pressures. Yes, this means that a desired animal is being selected in that circumstance; no, that doesn't mean that selection pressures are necessarily forcing changes upon the beast.
A zoo could maintain the same otherwise-extinct tortoise for millenia, for instance. Must you grumble that the tortoise is merely being selected, as if that has some bearing (it doesn't) on the debate at hand?!
Semantics is only one step above arguing about spelling, which is only one step above name-calling. Surely you want to raise yourself in this debate rather than sink like so many others...
I did a word search "alligator" on the page and saw no such reference.
Oh good grief.
Here: if a species has ZERO mutations, then it will have ZERO speciation. If a species has only 1 mutation in 20 million years, then it will have only 1 chance for speciation. If a species has only 2 mutations, then there can not be more than 2 speciation events.
There's your ascending line. 0, 1, 2 (at most).
What a waste of time. How pathetic that your argument is so bad that I have to spend time typing out the above...as you play dumb for lack of any better strategy.
So be it.
You did a deliberate word search on "alligator" on a web page for Crocodylia?! Yet another Darwinist deliberately playing dumb in some feeble attempt to make a point or drown this poor debate in a sea of semantics.
Ridiculous.
"No, they can't." - CarolinaGuitarman
Here you go: Labs and zoos can eliminate **natural** selection pressures.
Was that so hard?!
Must you continue to play dumb to make some nonsensical point?! You've known all along what I meant, yet played dumb anyway as if you didn't.
Pathetic.
Now, at 200,000 mutations, which is more important? Draw your straight line through there! Cherry-picking data, huh? Do you do research for Al Gore on global warming, too?
Oh, and I'll expect an apology from any good Christian who falsely accuses someone of something they did not say or do. As you did in post #330 (as I pointed out in #349).
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