"Imagine yourself in the Cretaceous period," says paleontologist Alan Grant in the opening minutes of Steven Spielberg’s "Jurassic Park." Played by a suntanned Sam Neill, Grant is explaining to a mouthy kid what it would feel like to be hunted down by velociraptors, the wily dinosaurs that have since terrorized millions of moviegoers worldwide.

"The point is, you are alive when they start to eat you," says Grant. "So, y’know — try to show a little respect."

Twenty years after its release in the summer of 1993, "Jurassic Park" stomps back into theaters today in 3-D and IMAX. It’s surely the opening salvo in Universal’s publicity campaign for next year’s planned sequel, "Jurassic Park 4," but it’s also a chance to see whether Spielberg’s big, brainy, science-savvy blockbuster will command respect from modern audiences. Will the movie’s pioneering computer-generated effects still dazzle in 2013? Will its notions of cutting-edge technology pass the smell test? And beyond its massive popularity — $914 million in ticket sales, a box-office record not broken until James Cameron’s 1997 epic "Titanic" — what is the larger legacy of "Jurassic Park"?

"It’s a real watershed for popular culture," says Matthew Carrano, curator of dinosaurs at the Smithsonian’s National Museum of Natural History in Washington, D.C. "Dinosaurs were always popular with children, but post-‘Jurassic Park,’ dinosaurs are much more acceptable across the board. Now there are adults who find dinosaurs interesting, and aren’t embarrassed about it."

"Jurassic Park" captured imaginations of all ages with a simple premise: A wealthy entrepreneur, John Hammond (Richard Atten­borough), is bringing dinosaurs to life after 65 million years of extinction. Using tattered dino DNA taken from ancient mosquitoes preserved in amber, and plugging the gaps with fresh frog DNA, scientists can clone everything from a galloping Gallimi­mus to the towering Tyrannosaurus.

Hammond’s dream is a dinosaur theme park, though several humans — including Laura Dern and a pre-fame Samuel L. Jackson — find themselves living in a splattery nightmare.

It’s based on a book by Michael Crichton, the late Harvard-educated doctor turned author and filmmaker, whose stories often mixed science fiction with real facts. "The Andromeda Strain," his best-selling book of 1969, imagined an extraterrestrial microorganism that clots human blood; his 1981 thriller "Looker," which he wrote and directed, wondered what would happen if 3-D digital modeling were applied to humans.

"Jurassic Park" was even more believable. By 1993, scientists already had been extracting DNA fragments from amber-encased creatures, including a 30-million-year-old termite. "Jurassic Park" met with some mockery — "Frogs are amphibians, dinosaurs are reptiles," fumed paleontologist Stephen Jay Gould, dissecting the movie in The New York Review of Books — but lay audiences were convinced. Even Gould admitted, "The dinosaur scenes are spectacular."

"Plausibility was paramount," says David Koepp, who co-wrote the screenplay with Crichton. "The DNA idea about mosquitoes and blood, you get it. You take one look at it and you just understand. That removed the movie from the Godzilla type of movie, where you say, ‘Well, there’s some kind of radiation, and he starts stomping bridges.’ This took things into the realm of science fact."

Underscoring the film’s authenticity was John "Jack" Horner, the paleontologist widely credited as the inspiration for the character of Grant. The fictional paleontologist, who insists dinosaurs were close cousins to birds, certainly sounds like Horner, who in the mid-1970s helped excavate a new dinosaur genus, the nesting Maiasaura. Horner served as a consultant on the film (and all its sequels, including No. 4) and claims credit for Grant’s trademark accessories, the straw hat and red neckerchief.

"My job was to make sure the dinosaurs looked as accurate as they could for the science we had at the time," says Horner, curator of paleontology at the Museum of the Rockies in Bozeman, Mont. "Steven had them behave the way he wanted them to behave, but my job was to make sure they looked good and to make sure the actors pronounced their scientific names right."

The outlandish character of chaos theoretician Dr. Ian Malcolm, memorably played by Jeff Goldblum, has been compared to several real-life mathematicians — from Mitchell Feigenbaum to James Gleick, author of the 1987 best-seller "Chaos: Making a New Science" — but Malcolm’s aggressive sexual energy and rock-star arrogance were exaggerated for the movie, according to Koepp.

"It was a challenge, from the writing and acting standpoint, to present anybody who was remotely interesting next to the dinosaurs," says Koepp. "If anyone comes out and starts talking about their personal life, you’d just wish they’d be quiet so you could look at the dinosaurs. But he could hold his own opposite the prehistorical wonders."

"JurassicPark" has gone down as one of the most aggressively merchandised films in history, but Carrano, the 43-year-old curator at the National Museum of Natural History, sees a different legacy.

"I probably have a job because of that," he says. For decades, museums regarded dinosaur paleontology as a marginal field, and few bothered to hire experts onto the staff, according to Carrano. After "Jurassic Park," however, "museums responded. The major museums, just about everywhere you can think of in a sizable place, have all brought somebody in over the last 20 years."

He adds: "It’s always challenging to connect people with science. And I think ‘Jurassic Park’ has done us a big service."

REVIEW Going back to turn Steven Spielberg’s 20-year-old dino thriller "Jurassic Park" into a 3-D spectacle (required to watch with, yes, 3-D spectacles) is almost as egregious an error, it turns out, as going back and bringing tyrannosaurs and triceratops to life again in the first place. ‘JURASSIC PARK 3D’ Rated: PG-13 Opens today You’re not going to lose a limb like poor chain-smoking computer nerd Samuel L. Jackson does in the movie, but you may lose your patience while you’re sitting there in the dark. Remember the seamless way those gallimimuses (or is that gallimimi?) stampeded across the verdant Isla Nublar field, almost mowing down Sam Neill and those two kids? Remember when that same trio is perched in the high branches of some Cretaceous-era tree, gazing out on a horizon dotted with a herd of giant grazing brachiosaurs? Visual effects technology was downright primitive back in 1993. But the CG artists, model artists, matte painters and digital renderers — Spielberg’s whole talented crew — managed to create the illusion that Richard Attenborough’s genetically engineered theme park off the coast of Costa Rica was real. Ironically, "Jurassic Park’s" 3-D conversion actually undermines that illusion and compromises the experience. When Spielberg and his great cinematographer Dean Cundey shot the film in Hawaii in 1992, they weren’t thinking 3-D, and so foreground and background, actors, props and animatronic beasties were framed and shot with a traditional 2-D viewing in mind. And, of course, with the dino visual effects in mind, how to make those raptors and tyrannosaurs look as if they’re really commingling with Laura Dern, Jeff Goldblum, Wayne Knight and all. But the "depth mapping" and depth-image rendering required for a 3-D conversion (which typically runs $10 million to $15 million) exaggerates and re-emphasizes the way those scenes are composed. Now, when that giant T Rex bears down on the two Jurassic Park Jeeps and their scared-silly passengers, the 3-D retrofit makes the scene look phonier, cheesier, almost like 1950s sci-fi. The fakery becomes more apparent. Yes, there are some close-up scenes — the raptors in the Jurassic Park kitchen, stalking kiddie stars Joseph Mazzello and Ariana Richards, and that poor, sickly triceratops that Neil and Dern hug and poke — that benefit from the 3-D-ization. But mostly, if you factor in the dimming effects of the 3-D glasses (everything less bright, less vivid) and the reformulated depth-of-field perspectives, "Jurassic Park 3D" does this fun, scary, innovative family film a disservice. Get the original from Netflix and save yourself some dollars — and disappointment. P.S.: When "Jurassic Park" was released in 1993, I gave it three stars out of four — that rating still stands. ——— Review by Steven Rea, The Philadelphia Inquirer