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In Jurassic Park, in the scene when the T-Rex escapes from the paddock and attacks the broken down cars, Dr Grant tells Ian Malcolm not to move, as the T-Rex's visual acuity is based on movement. How do we know this to be true? Was this an invention of Michael Crichton's for the novel, or is this an accepted theory in paleontology?

If this question should be moved to another more suitable part of the site, please let me know.

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I was going to suggest that maybe Dr. Grant learned about this when he visited the cloning lab, but googling for info, someone mentioned that Grant brought it up in the scene at the beginning where he scares the kid with the description of Velociraptor, which was before he knew anything about Jurassic Park. If you go to 0:38 in the clip here, you can see he tells the kid "you keep still because you think that maybe his visuality acuity is based on movement, like T. rex, and he'll lose you if you don't move". – Hypnosifl Jan 26 at 8:09
To clarify, this wasn't just in the movie, but book as well. See my comment to RiddlerNewCorners answer – Shantnu Tiwari Jan 26 at 13:06
Its interesting that Peter Jackson leveraged this Jurassic-Park based false "common knowledge" implicitly in the V-Rex chase scene, where Ann Darrow lays still and the V-Rex walks right away missing her completely -- watch it here – zipquincy Jan 26 at 19:14
@Shantnu Tiwari - Yes, but it was stupid of the movie to present this as something paleontologists could somehow know based on fossils, rather than presenting it as something scientists noticed about living dinosaurs after cloning them as in the book (see Richard's answer). And even that element of the book is kind of biologically ignorant in its own way if you understand that similar adaptations in different species are likely to be inherited from a common ancestor, see my point in the comments of RiddlerNewComer's answer about the common ancestor of crocs and birds being a dino ancestor too. – Hypnosifl Jan 26 at 19:16
If they can't see things unless they move...they must run into a lot of trees. – Tim B Jan 27 at 17:04
up vote 55 down vote accepted

Unfortunately, Dr Grant was wrong, and this theory only comes from Jurassic Park and is not accepted at all in paleontology.

I will use this article , but there are a lot similar on the web that answers the same question.

T-Rex can actually smell and their sense of smell is very developed, so the don't move theory is already broken by that fact.
Furthermore, he has front-facing eyes, and his binocular range was 55 degrees which is actually greater than that of a hawk.

You can find other crispy details in this article if you want some more infos!

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IIRC there was (at least in the book) a mock-explanation based on Jurassic Park's use of amphibian DNA, as apparently with toads and frogs vision is based largely on detection of movement (not that I actually know anything about frogs, or find that explanation in any way believable). – Eike Pierstorff Jan 26 at 8:59
The fact that you are using present tense to describe T-Rex's abilities scares me. – Mr Lister Jan 26 at 9:52
To add: In the 2nd book (The Lost World), Michael Crichton changed the story, so now the T Rex could see non-moving animals. When I read it, I found it quite strange, but no doubt scientists moaned at Crichton, so he fixed it in the 2nd book. – Shantnu Tiwari Jan 26 at 13:05
Also bear in mind that the book was published in 1990 (movie released in 1993) while the cited article is from 2014. Our understanding has likely progressed a long way in 26 years, and just because we know better now doesn't mean it didn't make sense at the time. I concur with both @EikePierstorff and ShantnuTiwari, Dr. Grant specifically cited frogs as his reasoning for movement-based vision, and it was corrected in the sequel (published 1995). – aherocalledFrog Jan 26 at 14:30
@aherocalledFrog: I know math is that way, but I still gotta point out that 2014-1990 is 24, not 26. Sorry for being so anal. – sbi Jan 26 at 15:21

The movie's source novel makes it clear that Grant didn't know it beforehand, he worked it out from observations, like the good little scientist that he is:

The tyrannosaur bellowed in the night air.

But by now Grant was beginning to understand. The animal couldn't see him, but it suspected he was there, somewhere, and was trying with its bellowing to frighten Grant into some revealing movement. So long as he stood his ground, Grant realized, he was invisible.

As to why the dinos have this peculiar visual impairment, it's described (by Harding) as being something that relates to their amphibian-like physiology:

Harding shrugged. “They probably wouldn't react. Dinosaurs have excellent visual acuity, but they have a basic amphibian visual system: it's attuned to movement. They don't see unmoving things well at all.”

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Wow, that's pretty far off. I wonder why I never noticed that when I read the book? Maybe it was because of my basic lancelet visual system. – Rex Kerr Jan 26 at 20:23
@RexKerr - I'm wondering if it's because the words were static on the page. – Valorum Jan 26 at 20:25
Can you please animate that with some JavaScript or something? I'm having trouble understanding you. :) – Rex Kerr Jan 26 at 20:27
@RexKerr Actually, I'm pretty sure I read an admission by Crichton that it was one of his scientific errors in the foreword to The Lost World (and humorously, Ian (resurrected for the sequel - in the original novel, he was presumed dead at the end), mentions that this is obviously absurd). I'm not sure if it was simply a mistake of his, or if the prevalent opinion at the time was that T. Rex indeed didn't see static objects. In any case, you probably read the original novel, rather than the "Book of the movie" version, where this was retconned (and Ian didn't die). – Luaan Jan 26 at 20:58
I like to think of it this way: Grant had seen enough to know if he moved, he was dead for sure. May as well try staying still. – Joel Coehoorn Jan 27 at 3:00

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