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.
b
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.
"Now, if you want to talk about random mutations, that's a more worthy topic of debate."
The two are intertwined, inseparably. I think you know this, but can't give in even an inch or your entire facade will crumble.
"Random (or not) "selection" is unworthy, however. It's non-controversial."
I never said it was controversial. I said that you were ignoring it's affects.
Keep flailing. The lurkers need some entertainment too.
He's stuck in a self-dug lying rut and cannot under any circumstances admit error lest he be damned to Hell for all eternity for being the troll that he is. So it goes with trolls.
Probably not that many compared to the other kinds of dinosaurs if they followed the usual rules about numbers for predators vs prey animals.
The big question about how tyranosaurs lived is how they would have hunted without having useful forelimbs. In today's world, hunters with teeth and claws (cats) can take on large prey singlehandedly while predators with just teeth (wolves and dogs) generally hunt in packs. Picture a pack of tyranosaurs coming after you?
I have no clue. But I am sure that there is a palaeontologist out there who could help you out...given that we think that Sue was about 25 years old at time of death, we have a pretty good idea as to max life spans of a TRex...the question of how often it bred and what amount of square miles could support each individual are questions that can never be answered, but I am sure that we can make some assumptions and work up a numerical range for you.....however math is not my strong suit...what are you getting at, anyhow?
Says you... Here's what the Reuters article had to say:
Paleontologists forced to break the creature's massive thighbone to get it on a helicopter found not a solid piece of fossilized bone, but instead something looking a bit less like a rock.When they got it into a lab and chemically removed the hard minerals, they found what looked like blood vessels, bone cells and perhaps even blood cells.
"They are transparent, they are flexible," said Mary Higby Schweitzer of North Carolina State University and Montana State University, who conducted the study.
She said the vessels were flexible and in some cases their contents could be squeezed out.
"The microstructures that look like cells are preserved in every way," added Schweitzer, whose findings were published in the journal Science.
"Preservation of this extent, where you still have this flexibility and transparency, has never been seen in a dinosaur before." Feathers, hair and fossilized egg contents yes, but not truly soft tissue.
Studying the soft tissues may help answer many questions about dinosaurs. Were they cold-blooded like reptiles, warm-blooded like mammals, or somewhere in-between? How are they related to living animals?
"If we can isolate certain proteins, then perhaps we can address the issue of the physiology of the dinosaur," Schweitzer said.
That's incorrect. Selection pressure could be from a volcano spewing ash into the air, or from a climate change, but "Selection" doesn't make any change to any species...it merely culls out those entities that have or don't have certain pre-existing genetic structures.
To actually change the genetic structure..to actually change a species, you have to have physical changes in the make-up or sequencing of the DNA itself (e.g. genetic mutations).
Without mutations, you can't have speciation. You can only have more or less of an existing population.
Nice try, though.
I believe that 'pack hunting' is dictated by the available prey (ie, Giganotosaurs appear to have lived in family groups, which makes sense when the prevalent herbivore was a Titanosaur - Argentinosaurus - which could grow to 10 times the size of the largest Giganotosaurus)...if the prey is smaller, solo hunting appears to be more common...with TRex its an open questions because without a doubt both ceratopsians and Hadrosaurines in the late cretaceous could get VERY big indeed, though the ration was a lot closed to 1:1....I guess we won't know for sure unless someone finds a pack of Rexes burried by a flash flood (which did in the two Giganotosaur groups that Dr. Coria found in Patagonia...)
Okay, just for the sake or discussion, let's say the T. Rex's average life span was 25 years and a heterosexual couple of T. Rex's spawned one t. Rex in their lifespans. So at minimum, there would be one new T. Rex every 25 years. At that rate, how many T. Rex's would have been born in 5 million years?
Incorrect. Again, you are unaware of the effects and interplay of mathematical probabilities on **random** mutations.
Thus, I'm not ruling out the impact of "selection." Instead, I'm factoring in the mathematical randomness of mutations.
Better vision in an alligator would not be "selected" out, for instance, contrary to your setup above. Such a random mutation would survive.
Thus, if a species remains unchanged over vast amounts of time, an answer **other** than "selection" must be present.
You got me. it all depends on how many you are STARTING with, and what rate of growth was average as the population expanded into new territories (using your examples the Rexes would have gone extinct pretty fast......)
The initial press releases were before the hard-core evo-losers had time to get to the researchers. I view them as more accurate than whatever came later.
I will not be more specific because you were rude in pinging me with an atheist ping. I would pray for you but I have bette things to do.
Knock it off!
Since no species has remained unchanged over vast amounts of time, you have just proven that there is no **other**.
New body types in the fossil record are almost always associated with extinction events or geological events that produce isolation.
Breeding experiments by humans demonstrate that physical size and shape can be modified in decades rather than mellennia. The key difference between rapid and slow change is selection and changes in the conditions that determine reproductive success.
There are genomes that are more plastic than others. Dogs can be shaped rather easily, but cats have pretty much the same body shape. The answer to why this is will be found by research rather than by speculation.
Really?! In what specific, different way is an alligator that is alive today from that of its direct ancestral grandmother 20 million years ago?
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.