Update 6/13/2017: I’ve changed some grammatical errors per suggestion from “alexauther94” on Discord and added an additional source that I had forgotten.


Velociraptor mongoliensis skeletal by Scott Hartman.

In Micheal Crichton’s 1990 novel, Jurassic Park, the characters are terrorized in the later half of the novel by a pack of six-foot tall, cunning Velociraptors with steel crushing jaws. Despite being heavily fictionalized, particularly in terms of size, the character Dr. Henry Wu — the lead geneticist of the dinosaur park — identifies the species of raptor the park as Velociraptor mongoliensis during the tour of the nursery that had a juvenile raptor as its resident:

Velociraptor,’ Alan Grant said in a low voice.

Velociraptor mongoliensis,’ Wu said, nodding. ‘A predator. This one’s only six weeks old.’

The book also gives the location of the amber that produced the raptors:

Ellie said, ‘But the animals we just saw, the velociraptor — you said it was V. mongoliensis?’

‘From the location of the amber,’ Wu said. ‘It is from China.’

Though the book itself identified the raptor species, some fans created their own explanations due to the differences between the novel’s raptor species and V. mongoliensis. One such explanation was by the JPEncyclopeida on fansite Jurassic Park Legacy (now defunct and the has Encyclopedia been resurrected on its own domain Jurassic-pedia since 2017) which stated that due to differences from the real V. mongoliensis it warranted them to be classified as a mutant with the possibility of Deinonychus DNA.

But the most well known and believed is that the Novel Raptors was based on a then undescribed Achillobator.

History of the Theory

Achillobator giganticus skeletal showcasing known remains by Jamie Headden.

The theory was started by Tamara Henson,  who owned and read the first Jurassic Park novel and Gregory S. Paul’s 1988 book Predatory Dinosaurs of the World, or as it is most commonly abbreviated “PDW”.

Paul is mentioned in the acknowledgments section of Jurassic Park and his classifications from PDW can be seen in use in the book itself. These instances being Procompsognathus having a plural form “procompsognathids”, a reference to Paul’s classification of Procompsognathus as being the sole members of its own separate family, and the mentions of Velociraptor in Montana, an allusion to Paul’s classification of the North American dromaeosaurid genera Deinonychus and Saurornitholeses as being species of Velociraptor with the character Dr. Alan Grant stating in the novel that Deinonychus is “considered one of the velociraptors now.”

On page 366 of PDW, Paul writes of undescribed specimens of what he classified as Velociraptor in the very Latest Cretaceous of Western North America. Paul then writes of specimens held at the American Museum of Natural History that are of large size, including a specimen which caught Henson’s attention:

Also at the AMNH is a hyper-extendable toe bone from the Late Cretaceous of Mongolia that looks like a Velociraptor somewhat bigger than V. antirrhopus [Deinonychus].

Henson came to the conclusion that this specimen from Mongolia was not only the inspiration for the Novel’s dromaeosaurids but was also an undescribed specimen of Achillobator giganticus, a dromaeosaurid from the Late Cretaceous of Mongolia. Discovered in 1989 and described over a decade later in 1999, Achillobator lived during the Late Cretaceous of Mongolia and was among the largest of the dromaeosaurid theropods.

Henson first posted about her belief on October 19, 2011, as a comment on a blog post by Trish Babbles and the next day made a thread on Modding Genesis forums about the subject. She later contacted David Kowalski “Dinos4Ever”, a moderator at Jurassic Park Legacy and a contributor to the JPEncyclopedia, to do a fact check, to which Dinos4Ever came to the same conclusion as her. He gave his reasons in an edit on Jurassic Park Wiki in 2012:

  1. Because the yellow amber, which contained the Raptor-DNA, was found in China, the Velociraptor species of Jurassic Park are called ‘mongoliensis’. This is in reality also the name of the type species of the Velociraptor genus, however, [it] is not the only species of Velociraptor according to Gregory S. Paul [in the late 1980s].
  2. Deinonychus didn’t lived [sic] in Asia, so this Chinese amber could only contain raptor-DNA from Velociraptor mongoliensis or Achillobator giganticus, since Velociraptor and Achillobator lived in China, Mongolia and Russia, which are Asian countries.
  3. In 1989, Gregory S. Paul classified remnants of a yet undescribed specimen of Velociraptor from China that was larger than Deinonychus in his book Predatory Dinosaurs of the World. Michael Crichton lists this book among his references for when he wrote Jurassic Park. This undescribed specimen is later attributed to Achillobator giganticus.
  4. Only Achillobator is known to reach the size of the animals in the Jurassic Park novels.

The JPEncyclopedia then came to believe the claim as fact stating that it was ” consistent with what Henry Wu describes of the amber the raptor were bred from originating from Chinese rock, which is the type of rock that produces Achillobator.”

The Flaws

As good as it may sound to some, the theory is heavily flawed.

First and foremost, Achillobator was first discovered in 1989 whereas Predatory Dinosaurs of the World was published in 1988, a year prior to the remains being discovered.

As for the specimen that Paul writes of matches the description of AMNH 6572, a phalanx D-II discovered by E. H. Colbert from the Iren Dabasu Formation of Mongolia in the 1930s, which John Ostrom stated was comparable to Deinonychus but was possibly twenty percent larger. Prior to Ostrom, Gilmore had reported in 1933 fragmentary fossils of dromaeosaurids in the Iren Dabasu. In 1993, Currie and Eberth wrote that dromaeosaurid remains were common in the formation with most being attributable to Velociraptor though there are larger teeth that they suggested belonged to a second indeterminate species of large dromaeosaurine dromaeosaurid. Given that AMNH 6572 comes from a different formation than Achillobator (which is found in the Bayanshiree Formation) and the fact that this specimen is identical to the description Paul gives to the Mongolian toe bone he mentions in PDW, it is most likely not Achillobator. There is also no known confirmation that Michael Crichton had the toe bone in mind when he conceived the Velociraptor.

As for the claim that Achillobator matches the size of the JP Novel raptor species, The Lost World map gives the length of the raptor species as 6 feet (2 meters), comparable to Velociraptor mongoliensis, whereas Achillobator giganticus is currently estimated to be about 16.4-19.7 (5-6 meters) ft in length.

Finally, Achillobator has only been found in Outer Mongolia, meaning that it could not be the fictional raptor in question. No remains of this genus have been referred to from Russia nor China. Teeth attributed to V. mongoliensis have been found in China in the 1950s, though Mickey Mortimer of the Theropod Database has disputed that these teeth belong to Velociraptor. However, Mortimer still considered them dromaeosaurid nonetheless and the fact still stands that these were classified as V. mongoliensis.

Enter Deinonychus

Deinonychus antirrhopus skeletal by Scott Hartman.

What makes the theory lose credence further are comments made by Paleontologist John Ostrom who was acknowledged by Crichton in Jurassic Park. In a 1997 interview with The New York Times, Ostrom spoke of a meeting he had with the author in regards to the Raptors:

I was in my office when the telephone rang one morning. ”Professor Ostrom, this is Michael Crichton.” And we had a very interesting conversation. I had read ”The Andromeda Strain.” So he explained to me that he was writing another novel, and he was calling to find out about the creature that I had discovered in Montana a few years back, that he understood it was a meat eater. Could it run as fast as you or I, could it jump as high? I told him what I thought that this creature might do, or be able to do.

The name I gave it was Deinonychus, which comes from the Greek and means ”terrible claw.” And Michael Crichton, in an apologetic way, explained that in the novel he decided to use the name Velociraptor, that I had said was the closest relative to the animal I had found. He said, ”It’s more dramatic.” And I said I recognize that most people are not familiar with Greek. Velociraptor everybody recognizes.

Though many concluded this occurred during the writing of the first novel, in 2016, Richard Conniff reported that Daniel Brinkman, a paleontologist at the Peabody Museum, had uncovered letters that revealed that this meeting occurred during the writing of the second novel The Lost World. Ostrom congratulated director Steven Speilberg and Micheal Crichton for their success with the film adaptation of Jurassic Park and invited both men to see Deinonychus at the Peabody Museum. Soon afterward Crichton contacted Ostrom about the dromaeosaurid during the writing of the sequel.

It has been said prior to this revelation that Crichton had based the Raptors on Deinonychus since the first novel with Brian Switek being a notable proponent of this claim. Additionally, Richard Andersson, known as “Hellraptor” in online circles, has said that he contacted Dr. Thomas Holtz about the basis of the raptors and Holtz replied that it was based on a large specimen of Deinonychus. Tom Parker has mentioned in January 2016 a source he could not find where Crichton was “apparently on record” for basing the size of his fictional raptors off of a large Deinonychus from the Cloverly Formation mentioned in PDW. In PDW on page 367, Paul writes of a Deinonychus specimen that is 11 ft in length and of “male-timber-wolf mass”.

Given Brinkman’s discovery in 2016 and what Ostrom has stated, I have my doubts that Deinonychus was the original basis. and the large specimen that has been mentioned may have been the basis for the raptors in The Lost World.


In conclusion, as much as some may try to a find a real basis for the raptors of Crichton’s novels, they are an entirely fictitious portrayal of a real animal. From what I’ve gathered, the raptors of the first novel were sized-up V. mongoliensis from China and then for the second novel Crichton changed its basis to Deinonychus (though he may have used the size of a large specimen as the basis of the raptors’ size in the first novel). Their large size could have been based on the undescribed Mongolian toe bone mentioned in PDW, but there is no confirmation of this I could find and given the evidence, it seems unlikely.

As for an in-universe reason for the raptors size, I’ve personally interupted it as being a genetic modification. Wu in the book spends most of the chapter of “Version 4.4” trying to convince Hammond to go to the next genetic version with the proposal to make the dinosaurs slower because of the public’s current perception of dinosaurs. The raptors of the first JP novel could have simply been V. mongoliensis from China that was modified by its creators for the sake of entertainment.

But as enjoyable it is to speculate, the fact is that the inhabitants of Crichton’s Jurassic Park are not entirely reflective of their real counterparts. In the Raptor’s case, not only is it a V. mongoliensis/Deinonychus taller than any specimen found, but it also has a bite force that can crush through steal and bears pebbly, scaled skin that can change color, traits which have never been found in dromaeosaurids. Not everything in the novels has a scientific basis, one famous example being Dilophosaurus’ venomous spit.

I end this post with the first reply to Henson’s thread on Modding Genesis:

JP raptors aren’t any extinct form of dromaeosaurid. These raptors are meant to terrorize the audience as a “perfect predator”, a beast you can’t hide from, where your intelect is of little help. A trex? for all its might, you just have to find a sturdy building. A raptor? Not as easy.
That said, if they call it a velociraptor, it’s a velociraptor. Just not the same velociraptor as the one that lived in Mongolia during the Cretaceous.


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