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.
"If not, what evidence gives them the conviction to state such opinions as athoritative fact rather than wild speculation?
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Skull details can tell a lot about the size and shape of the eyeball. Further, the position of the eyeballs in the skull, along with the grooves mentioned in the article can indicate what the animal's field of vision was.
As for the predator aspect, take a look at a cat or dog, then a rabbit. The predator has eyes that face forward, as do those of the T. Rex. That allows good 3-dimensional vision. The rabbit, on the other hand, has its eyes on the sides of its head. Their field of vision is almost 360 degrees, but they have poor 3-dimensional vision.
The prey animal has evolved to detect motion in a wide angled view. The predator animal has evolved to focus on the prey animal and track its movements.
Given a rabbit skull and a cat skull, any first year student can immediately identify which is the predator and which the prey.
Well, at least those scientists admit past mistakes and get on with it.
It is a side effect of our conscious, and our early training, that we think we are the smartest and most intelligent creature on Earth.
Now we are starting to see that predatory dinosaurs were smart, fast, skilled at hunting. Most predators must be smart, fast, and skilled at hunting or they go extinct.
Sure, we are clever and good at making tools.
But to believe any other life form is not intelligent, or not as 'smart' as a human, is a mistake that can be fatal.
One of the smallest life forms (and therefore possesing the 'smallest brain') appears to be more intelligent than humans, and is always ahead of the game in the battle between us and them.
It is the virus.
TRex was a scavenger! Hah! Next thing they're going to try to sell us was TRex was gay, or it was really TRex who authored the plays of William Shakespeare. Then they'll start the old saw again about how Shakespeare was gay. It wouldn't surprise me if someone surmises that if Shakespeare was gay and TRex was gay, then Shakespeare must have been a TRex.
Can't wait.
"If T-Rex was a vegetarian, as Hovind asserts, it was certaintly not a predator."
I saw this old movie once where these guys went to some island where all the prehistoric stuff was still alive and everything. Some of the plants were, like, you know, really agressive.
I love the scene where TRex eats the lawyer!
Oh, no, not true at all--TRex could, in fact, do long division. ;)
I'm sure Shakespeare had happy and light hearted moments.
"Pack-hunting is a possibility, but I don't know if there's much evidence for it."
I agree that T-Rex probably was both a predator and a scavenger. As far as pack-hunting, what were the majority of potential prey animals in North America when T-Rex lived? There were thousands and thousands of Hadrasaurs, which migrated from North Western Canada south into the US, and back again.
Helps sell books.
I saw that too. The plants grabbed people and ate em.
I think a cat's vision is like that. Some kind of feedback loop that makes their eyes turn and look towards movement.
It's a fine example. Alligators only have one (Spring) breeding season. They breed slow and they are little changed in 200 million years. Hmmm...
>>At the beginning of the T Rex species, middle, or at extinction?<<
Well now I'm confused. Didn't eagles evolve from T-rex? That would make T-rex the middle, right?
Oh, and I'm joking...
On the contrary, you have nothing to support a faster T Rex birth rate, whereas I can show that alligators breed slower than smaller reptiles.
D'oh! Don't you hate it when the tables are turned?!
That's odd. My mother-in-law also had bird-like, binocular vision.
I thought the part before "blah blah blah" was good.
"It's a fine example. Alligators only have one (Spring) breeding season. They breed slow and they are little changed in 200 million years. Hmmm..."
Lots of animals are much as they were. Evolution does not mean that every species changes dramatically.
As for speed of breeding, Alligators produce numerous eggs each year. They're actually fairly prolific breeders. They have to be, since most of the young are eaten shortly after emerging from the egg.
If, as you say, alligators have been around for 200 million years, that is 200 million generations. And that's a lot. We have alligators that are pretty close to their 200 million year old ancestors. That demonstrates that they are well adapted to their niche. They, like the coelacanth, survived because they were well suited to their environment.
That does not mean that other species did not evolve from those 200 million year old alligators, you see. It just means that alligators survived with few changes. Evolution is not a zero sum game.
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