Biological issues in Jurassic Park
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Jurassic Park, a book by Michael Crichton, with a film version directed by Steven Spielberg, revolves around the resurrection of dinosaurs via genetic engineering. Scientists and enthusiasts have brought up a number of issues with their facts and feasibility.
Halfway through the original text, characters John Hammond and Henry Wu have a discussion. Wu says that they could and should make better dinosaurs. Hammond scoffs at the idea, saying that they have real dinosaurs; who would want more? Wu's reply is that they should not bother with reality because the people coming to see the Jurassic Park do not want reality, they want their expectations.
It is also worth noting that many of the dinosaur species depicted in the film did not actually live in the Jurassic period.
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[edit] Dinosaurs
[edit] Velociraptor
The raptors in the novel, following through to the film raptors, were larger than the species going by the name because during the writing of the novel, a previously discovered dinosaur named Deinonychus (closely related to Velociraptor, but larger) was renamed as a Velociraptor species by some scientists, notably Gregory S. Paul.[1] Crichton wrote his novel based on the idea of a human sized raptor, but after the publication—when the movie was already in production—the idea of Deinonychus being a Velociraptor species was dropped.
During the movie's production, the effects supervisors acknowledged that the Velociraptor featured in the movie were sized identically to the larger Deinonychus. However, during the filming paleontologists came across a larger dromaeosaurid species named Utahraptor and the larger raptors remained, even though Utahraptor was substantially larger (21 feet long) than most of the movie's raptors. It should be noted, also, that at the start of the film a Velociraptor skeleton is uncovered in Montana - no examples of the dinosaur have been uncovered in the USA (although both Deinonychus and Utahraptor are American dinosaurs). The fossil skeleton is similarly inaccurately large. It is possible that the velociraptors in the movie are re-classified Deinonychus, though in the book they are said to be Velociraptor mongoliensis.
The high intelligence of the film's Velociraptor is considered somewhat unlikely by scientists, given the relative size of their brains and comparisons with modern animals.[2]
It is certain that Velociraptor had feathers.[3] Both the film and novel dinosaurs have scales, rather than feathers; however, both were created before the discovery of feathered dinosaurs closely related to Velociraptor (e.g. Microraptor).[4][5] In Jurassic Park III the raptor was remodelled and small feathers on the male's heads were included, while still looking similar to the original design.
As with other bipedal dinosaurs in the films, the hands of Velociraptor are depicted with the palms facing down and backwards, but this would have been anatomically impossible for the real animals, as their forearm bones (ulna and radius) could not rotate in this way. Instead, their palms would have faced each other, like a person about to applaud.[5]
[edit] Procompsognathus
The Procompsognathus are given several attributes in the novels that cannot be determined from the fossil evidence to date. They are presented as living and hunting in large groups; as scavengers and coprophagists (eaters of feces), useful in keeping the park clean of sauropod excrement; and as secreting a venom described as similar to that of a cobra, although more primitive. This ability to incapacitate their prey is absent in the films, where they are dropped in favour of Compsognathus.
In reality, Procompsognathus is known from a single partial skeleton from the Late Triassic of Germany, with a partial skull that may belong to it or, more likely, an early relative of modern crocodilians.[6][7] Because only one individual is known, there is no direct evidence that it lived in groups; however, related animals such as Coelophysis and Megapnosaurus have been found in groups of numerous individuals, such as at Ghost Ranch.[7] As there are no uncontroversial remains of the head of Procomposognathus, its diet cannot be inferred from the form of its teeth and jaws; other coelophysoids are seen as carnivores with skull adaptations that may have been advantageous when handling small prey.[7] Finally, aside from a possible theropod tooth from the Late Cretaceous of Baja California with grooving similar to that found on the teeth of venomous snakes and lizards,[8] there is no evidence for venom secretion in dinosaurs, and scientists consider it unlikely.[citation needed]
[edit] Dilophosaurus
The movie Dilophosaurus stands about 1.2 meters (4 ft) tall[9], while its real-life counterparts measured on the order of 6 meters (20 ft) long and 1.4 meters (4.5 ft) tall at the hips.[10] This was a deliberate deviation from accuracy for stylistic purposes, and to differentiate it from the Velociraptors.[9] It also has a totally speculative frill like the Australian frill-necked lizard. The novel's version is full-sized and lacks the frill. Both eject a potent, blinding venom in both their bite and their spit, like a spitting cobra, and use it to hunt; the novel acknowledges this as Crichton's creative license not suggested by fossil evidence.[11]
[edit] Brachiosaurus
The Brachiosaurus in the movie is shown to be chewing its food with a side to side motion of its lower jaw. In reality, it couldn't feed like this. Brachiosaurid skulls and jaws were limited to up and down motions, and their teeth were specialized for shearing and cropping plant material. Other sauropods, such as diplodocoids, could move their jaws backward and forward, but were probably using this motion to strip branches, not to chew plants.[12] Instead of processing food in the mouth, sauropods probably relied on taking in as much food as possible and processing it farther down the digestive tract, either through gastroliths (rocks swallowed and used for grinding in a gizzard-like organ; note however that this hypothesis, while common in the popular literature, is now considered unlikely in sauropods),[13] or simply by digestion through fermentation by microorganisms.[14]
Additionally, the Brachiosaurus head is shown much larger than its actual size in an up-close shot when Dr. Alan Grant, Tim Murphy and Alexis Murphy try to feed it. In the other shots of Brachiosaurus the head size is proportionate to the body.
[edit] Tyrannosaurus
The movie's theory is that the Tyrannosaurus rex would be unable to see someone if they were to remain still (this was explained in the novel as being another side effect of the splicing of frog DNA with that of the dinosaurs); however, evidence has shown T. rex to have had high visual acuity and binocular vision.[15] Some argue that it would still be able to smell them regardless.[16] In the sequel novel, The Lost World, it is suggested that the Tyrannosaurus can in fact see inanimate objects, and was actually not hungry. In fact, a character who specifically attempted this technique dies when the T. rex nudges him to see if he was there as Malcolm mentions that he was listening to "the wrong scientists."[17][18]
Tyrannosaurus is also shown as being able to keep pace with a jeep travelling at considerable speed; it is debated within the palaeontological community whether a T. rex could even achieve this speed, much less maintain it.[19] Anatomically, its short forelimbs would be unable to cushion an impact if it were to fall at speed; this could potentially be fatal. Animators at Industrial Light and Magic were forced to use optical illusions in order to make the Tyrannosaurus appear to convincingly run at that speed.[20]
[edit] Spinosaurus
The Spinosaurus in Jurassic Park 3 was, although shorter, stronger than the real animal. It was shown as a predator of T. rex, but its jaw suggests that it ate mainly fish, small dinosaurs and carrion. Also, its teeth are very straight, conical and crocodilian in reality; but they are hooked and serrated in the movie.
[edit] Pachycephalosaurus
The Pachycephalosaurus in The Lost World: Jurassic Park was downsized. Surprisingly, in Jurassic Park: Operation Genesis, the dinosaur was of correct size. It is possible that the pachys which are seen in The Lost World are juveniles.
[edit] Stegosaurus
The Stegosaurus in The Lost World: Jurassic Park was almost twice the size of the real animal.
[edit] Other reptiles
[edit] Pterosaurs
Like the Cearadactylus in the novel, the Pteranodon in Jurassic Park III is interpreted as aggressive and able to pick a teenager up with its feet (a similar scene was planned for the climax of Jurassic Park 2, but omitted after palaeontological advisors on the production declared that this would not have been possible). However, both pterosaur genera were thought to have eaten fish,[21] and were incapable of grasping with their feet. In reality it is unlikely a Pterosaur of any kind would have either the strength or motive to lift up a person. Also, despite the fact that the name Pteranodon means 'winged without teeth' or 'winged toothless', the Pteranodon in Jurassic Park 3 have small teeth in their bills.
[edit] Other issues
During a scene in the movie where traitorous park programmer Dennis Nedry steals the dinosaur DNA, some of the tubes on which the dinosaurs' names are printed have them spelled incorrectly, including Tyrannosaurus and Stegosaurus, as Tyranosaurus and Stegasaurus, respectively. The scene also shows Nedry opening up a liquid nitrogen-filled cryogenic container and handling the supercooled tubes without thermal gloves. Doing this can be quite painful and causes severe frostbite, but nonetheless can be done for very brief periods, as shown.
In the scene where a baby dinosaur hatches from an egg in the laboratory, Dr. Grant asks Dr. Wu, "What species is this?" Dr. Wu replies, "It's a Velociraptor." This is not strictly accurate: Velociraptor, by itself, is the genus, not the species, as it would need the specific descriptor mongoliensis appended to give the species name, in full, Velociraptor mongoliensis (or, if the raptors were Deinonychus, Deinonychus antirrhopus).
A similar issue occurs in the restaurant scene in the movie, in which Dr. Grant describes dinosaurs and man as "two species". As about 700 species of dinosaur have been discovered, dinosaurs and man are some 701 species.
[edit] Biotechnological background
The dinosaur DNA is extracted from fossilized mosquitoes, and this small amount is then amplified by polymerase chain reaction (PCR). This has been done before, for example with a Cretaceous weevil in Cano et al. (1993) (no dinosaur DNA was found).
There are some problems with this approach:
- The DNA featured in the movie is shown coming from a Dominican amber mine, though this mine is never stated to be the sole source. The novel indicates sources are global as Hammond's widespread purchasing and stockpiling of amber comes under scrutiny. Dominican amber is 10 million years to 30 million years old,[22] when dinosaurs died out 65 million years ago.
- None of the dinosaurs featured in the movie are known to have existed in the Dominican Republic 65 million years ago (though, again, whether that mine is the only source for DNA is unknown).
- The mosquito had to have had just one species of dinosaur as its food source to avoid a mix-up.
- The scene featuring a close-up of the mosquito clearly shows fuzzy antennae, meaning the particular insect is male. Only female mosquitoes, however, suck blood.
- It is unknown which dinosaur the sample contains. It would be impossible to tell which species it is, because the DNA sequences would fit somewhere between that of birds and crocodiles. The book does address this, stating that they "just grow it and find out", to mathematician and chaos theorist Ian Malcolm's annoyance.
- The dinosaur DNA has to be correct (it has to contain every chromosome) and should contain no sequence gaps. The book and movie did address this issue, however, and had the scientists use frog DNA to compensate for the gaps in the dinosaur DNA. However, this causes a problem, as the dinosaurs are then able to change sex (as the frogs from which the DNA was obtained were able to do) and reproduce, thus furthering the problems leading to the park's collapse.
- The DNA is mixed with mosquito, bacterial, and viral DNA. Although PCR is very specific, it is sensitive to contamination, and if the wrong primers are used, it will also amplify the other DNA.
- Because DNA is broken down by nucleases in the mosquito gut, the mosquito would have to be preserved immediately after feeding; this would be problematic for the park's scientists, although it would explain the lack of mass contamination in the individual samples.
Furthermore, in the fossilization process, molecules are altered. Nevertheless, amber is the best preservative, because organic material is preserved. But DNA cannot survive completely without gaps for tens or hundreds of millions of years.
Tens of thousands of DNA base pairs were recently sequenced from 40,000-year-old skeletal remains of cave bears without using PCR, establishing that, in principle, large-scale genomic sequencing of fossilized remains is possible. Of course, the remains used in this study are orders of magnitude younger than anything from the dinosaur era, and the technique might not extend to those creatures.
In the book the gaps in the DNA are filled by hybridizing the DNA with either bird, lizard, or frog DNA. In the movie, only frog DNA is used. This is extremely difficult, as one would need to know which dinosaur genes are homologous with frog genes. The use of frog genes was a plot device, to allow some females to change sex and breed nevertheless (although natural sex change is also possible in some more advanced vertebrates).
The dinosaurs were genetically altered so they could not produce lysine, forcing them to depend on lysine supplements provided by the park's veterinary staff. Most vertebrates cannot produce lysine by default as it is an essential amino acid.
The movie states that all dinosaurs are female because all vertebrate embryos are inherently female, requiring an extra hormone at the right phase to make them male. This is not technically true. Vertebrate embryos are undifferentiated, possessing organs that can grow into either male or female reproductive systems. In mammals, at a certain developmental stage the Y chromosome triggers a flood of testosterone, causing the fetus to develop into a male. If, for some reason this doesn't happen, the fetus will develop as an XY Female (See Swyer syndrome). Birds and reptiles (and presumably, dinosaurs) don't use Y Chromosomes in this way. In fact, they seem to use an opposite system with females possessing a W chromosome and a Z chromosome and males possessing two Z Chromosomes. In the scenario presented in Jurassic Park, it seems likely that all the dinosaurs in the park would have been functional males or sterile males possessing an extra chromosome (See Hermaphrodite).
The next step would be bringing the DNA strands to expression. For that, one would need to inject the dinosaur DNA into the nucleus of a fertilized egg cell of a close relative of dinosaurs (birds or crocodiles, not frogs). This technique is based on reproductive cloning, which was used to clone Dolly. In the movie, ostrich eggs are used for this purpose. However, the development of an embryo is regulated by hormones in the egg/uterus and the environment. These (bird or crocodilian) hormones need to have the same effect as their original dinosaurian counterparts. For that, they have to be able to recognize particular pieces of dinosaur DNA, a currently impossible task. New research in plastics, however, has allowed for the creation of synthetic eggs such as those that were used in the book.[citation needed] In the book Henry Wu claims that egg yolk is nothing but a growth medium that can be created in a laboratory. However, if it were this simple, an embryo could just be put into such a medium and left to grow 16 (A scene in the third movie seems to show that some embryos were placed in tanks and that the scientists achieved some success because the embryos did grow big enough to be visible[citation needed].) Extra hormones are needed from the original parent specimen, however, or constructed precisely from using the genome in order for the embryo to flourish.
[edit] References
- ^ Paul, Gregory S. (1988). Predatory Dinosaurs of the World. New York: Simon and Schuster, 464pp. ISBN 978-0671619466.
- ^ Larson, Hans C.E.; Sereno, Paul C.; & Wilson, Jeffrey A. (2000). "Forebrain enlargement among nonavian theropod dinosaurs". Journal of Vertebrate Paleontology 20 (3): 615–618. doi:.
- ^ Turner, A.H.; Makovicky, P.J.; Norell, M.A. (2007). "Feather quill knobs in the dinosaur Velociraptor" (pdf). Science 317 (5845): 1721. doi:.
- ^ Xu Xing; Zhou Zhonghe, Wang Xiaolin, Kuang Xuewen, Zhang Fucheng & Du Xiangke (2003). "Four-winged dinosaurs from China". Nature (421): 335–340. doi:.
- ^ a b Paul, Gregory S. (2002). Dinosaurs of the Air: The Evolution and Loss of Flight in Dinosaurs and Birds. Baltimore: Johns Hopkins University Press, 472pp. ISBN 978-0801867637.
- ^ Glut, Donald F. (1997). "Procompsognathus", Dinosaurs: The Encyclopedia. Jefferson, North Carolina: McFarland & Co, 729–731. ISBN 0-89950-917-7.
- ^ a b c Tykoski, Ronald B.; and Rowe, Timothy (2004). "Ceratosauria", in Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, Second Edition, Berkeley: University of California Press, 47–70. ISBN 0-520-24209-2.
- ^ Hecht, Jeff. Re: Venomous Therapsid. The Dinosaur Mailing List. (contains a copy of a draft of material author Hecht wrote for New Scientist regarding 2000 abstract and reaction)
- ^ a b Shay, Don; Jody Duncan (1993). The making of Jurassic Park. Ballantine Books, pp. 35-36. ISBN 1852837748.
- ^ Paul, Gregory S. (1988). "Genus Dilophosaurus", Predatory Dinosaurs of the World. New York: Simon & Schuster, pp. 268-270. ISBN 0-671-61946-2.
- ^ Chrichton, Michael (1990). Jurassic Park. Alfred A. Knopf. ISBN 0-394-58816-9. “It was Muldoon's view that some dinosaurs were too dangerous to be kept in a park setting. In part, the danger existed because they still knew so little about the animals. For example, nobody even suspected the dilophosaurs were poisonous until they were observed hunting indigenous rats on the island-biting the rodents and then stepping back, to wait for them to die. And even then nobody suspected the dilophosaurs could spit until one of the handlers was almost blinded by spitting venom.”
- ^ Barrett, Paul M.; and Upchurch, Paul (2005). "Sauropodomorph diversity through time", The Sauropods: Evolution and Paleobiology. Berkeley, CA: University of California, 125-156. ISBN 0-520-24623-3.
- ^ Wings O (2007). "A review of gastrolith function with implications for fossil vertebrates and a revised classification". Palaeontologica Polonica 52 (1): 1–16.
- ^ Carpenter, Kenneth (2006). "Biggest of the big: a critical re-evaluation of the mega-sauropod Amphicoelias fragillimus", in Foster, John R.; and Lucas, Spencer G. (eds.): Paleontology and Geology of the Upper Jurassic Morrison Formation (pdf), New Mexico Museum of Natural History and Science Bulletin 36, Albuquerque: New Mexico Museum of Natural History and Science, 131-138.
- ^ Stevens, K.A. (2006) Binocular vision in theropod dinosaurs. Journal of Vertebrate Paleontology 26(2):321–330
- ^ Jaffe, Eric. "Sight for 'Saur Eyes: T. rex vision was among nature's best", Science News. Retrieved on 2007-10-02.
- ^ Carpenter, K. & Smith, M.B. 2001. Forelimb osteology and biomechanics of Tyrannosaurus. In: Tanke, D.H. & Carpenter, K. (Eds.). Mesozoic Vertebrate Life. Bloomington: Indiana University Press. Pp. 90-116. (download here)
- ^ Derstler, K., and Miller, M.M. (2007). "Anatomy and function of digit III of the Tyrannosaurus rex manus." Geological Society of America Abstracts with Programs, 39(6): 77. Abstract.
- ^ Levy, Dawn (February 27, 2002) T. rex's new image: still ferocious, not quite as quick, stanford.edu
- ^ Hutchinson, J. R. and Garcia, M. (2002). Tyrannosaurus was not a fast runner. Nature 415: 1018-1021
- ^ Wellnhofer, Peter (1991). The Illustrated Encyclopedia of Pterosaurs (in English). Salamander Books Ltd, p. 159. “"They [known pterosaurs] fed on aquatic organisms. ... Fossilized stomach contents of some pterosaurs such as... Pteranodon, have been found, these being the remains of the last meal before they died. In all cases they are remains of fish."”
- ^ George Poinar, Jr. and Roberta Poinar, 1999. The Amber Forest: A Reconstruction of a Vanished World, (Princeton University Press)
- Cano R.J., Poinar H.N., Pieniazek N.J., Acra A., Poinar G.O. Jr. (1993). Amplification and Sequencing of DNA from a 120–135-Million-Year-Old Weevil. Nature, 363:536–538
- Weaver, R. F. (2002). Molecular Biology. McGraw-Hill, New York, p. 76. ISBN 0-07-234517-9
- Noonan, J.P., et al. Genomic sequencing of Pleistocene cave bears. Science 309(5734):597–599, July 2005.
- DeSalle, Rob; Lindly, David (1997). The Science of Jurassic Park and The Lost World Or, How to build a Dinosaur, pp 1-194. ISBN 0-465-07379-4.
[edit] Further reading
- The Science of Jurassic Park and The Lost World. Or How to Build a Dinosaur. Rob DeSalle and David Lindley. BasicBooks, New York, 1997. ISBN 0-465-07379-4.
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