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Production picture of the Rhedosaurus model used in The Beast from 20,000 Fathoms
A painting by James Bingham depicting the sea monster attacking the lighthouse in "The Fog Horn"
Name information
Alternate names Dinosaur,TFH The Beast, Sea Serpent,TBf2KF Rhedosaur,[1] Herman[2]
Subtitle(s) Atomic Monster
(原子怪獣,   Genshi Kaijū)[3]
Physical information
Species Dinosaur; extraterrestrial dinosaurPoD, PlesiosaurRBC
Height 40 feetTBf2KF[note 1]
Length ~90-100 feetTFH & RBC
~200 feetTBf2KF[1]
Weight 500 tonsTBf2KF[1]
Other stats Neck length: ~40 feetTFH
Tail length: ~100 feetTBf2KF[5]
Affiliation information
Place(s) of emergence Baffin Bay, the ArcticTBf2KF
Mesozoic Earth-like planetPoD
Enemies Humans, Tyrannosaurus rexPoD
Real world information
Conceived of by Ray Bradbury, Ray Harryhausen
Written by Ray Bradbury, Lou Morheim,
Fred Freiberger, Robert Smith
Designed by Ray Harryhausen, Eugène LouriéTBf2KF
Modeled by Ray Harryhausen,TBf2KF[7]
Stephen A. CzerkasPoD
Other information
First appearance Latest appearance
"The Fog Horn" Planet of Dinosaurs
1953:1977:More roars
Disclaimer: This page is for both the Rhedosaurus and the sea monster from "The Fog Horn" which inspired it. They are covered together for convenience.

The Rhedosaurus is a giant fictional dinosaur who serves as the antagonist of the 1953 American giant monster film The Beast from 20,000 Fathoms. It is based on a creature from the 1951 short story "The Fog Horn" by Ray Bradbury.

Following an American atomic bomb test in the Arctic Circle, the Rhedosaurus awakened from its 100 million-year slumber beneath the Arctic ice and headed down the North American coast, destroying everything in its path as it made its way to New York City, which may have been its original home. The Rhedosaurus wandered the streets, eating people and wrecking cars in its path. Attempts to kill it were complicated by an ancient disease it carried; spilling its blood freed the plague, which was almost as deadly as the reptile itself. The creature was eventually killed at Coney Island when a radioactive isotope was shot into a wound on its neck, both fatally wounding it and neutralizing the disease.

While only the antagonist of a single film, the Rhedosaurus became an iconic and globally renowned creation of Ray Harryhausen. It has consequently received many homages in comics, film, and television, and even inspired the first Godzilla and Gamera films. A smaller version of the dinosaur briefly appears in Planet of Dinosaurs (1977), in which it battles and is ultimately defeated by a Tyrannosaurus rex.


According to Rhedosaurus creator Ray Harryhausen, the monster's name may have been devised by The Beast from 20,000 Fathoms producer Hal E. Chester or one of the film's writers. He went on to say that some people believe the first two letters of Rhedosaurus's name were inspired by his initials, R. H.[8] In the film, the creature is dubbed the Beast and is initially nicknamed a "Sea Serpent" by a publication; it is also known as Herman,[2] and is sometimes referred to as a "Rhedosaur."[1]


The concept of "The Fog Horn" and its accompanying dinosaur were inspired by a visit author Ray Bradbury made to Venice, California in 1949, where he heard the fog horn sound after having seen the "bones" of the Giant Dipper roller coaster, which had been demolished three years prior.[9][10][11]

The producers of The Beast from 20,000 Fathoms, Jack Dietz and Hal E. Chester, were initially uncertain what kind of monster they desired for their film.[12] Animator Ray Harryhausen and director Eugène Lourié[12] made several sketches of a gigantic octopus, shark, and dragon-like creature.[7] Harryhausen did not wish for the beast to be a recognizable animal and instead wanted it to be a dinosaur, but not an Allosaurus,[12] Tyrannosaurus rex,[7] or Brachiosaurus, the latter because it would likely be compared to The Lost World (1925).[12][7] They eventually settled that the creature should resemble James Bingham's painting of the dinosaur in Bradbury's short story featured in The Saturday Evening Post. By combining elements of the artwork with added animal features, they invited a new, intentionally menacing dinosaur. Upon the film's release, the dinosaur was considered to be scientifically inaccurate, with Lourié having to explain to the Museum of Natural History why they did not instead include a depiction of a real dinosaur such as the Tyrannosaurus rex. According to Variety, he told them, "We wanted a brand new monster who looks more frightening than the real thing".[12]

Main article: Rhedosaurus/Gallery#Concept art.

Harryhausen created a clay model of the Rhedosaurus based on his sketches, but he and other staff members felt that it was "too kind, too babyish"[7] and "dog-like".[12] Thus, Harryhausen returned to his workshop to make a stronger, more terrifying version of the model. The new model was tested, but Harryhausen felt that it still wasn't right, creating a third and final version after discussion with Dietz and Chester.[7] Parts of the completed model were later repurposed for the fire-breathing dragon in The 7th Voyage of Sinbad (1958).[13][14][12] A five-second piece of stop-motion animation of the Rhedosaurus cut from the film appeared in the trailer for The Black Scorpion, released in 1957.[15]

For Planet of Dinosaurs, Stephen A. Czerkas constructed a new, smaller model that was used to battle, and ultimately be killed by, a Tyrannosaurus rex. According to animator Jim Aupperle, "Stephen and I both place the Rhedosaurus among our top favorite of Ray's myriad monsters. We felt that by giving the great Beast a cameo in our film we were acknowledging the immense debt we both feel to Ray. We had to make the Rhedosaurus more of a baby size because one as large as the original would have made a meal of our Tyrannosaurus instead of the other way around."[16] Harryhausen visited the set during filming.[16]


The creature from "The Fog Horn," upon which the Rhedosaurus is based, is said to have a 40-foot long neck, a body covered in crayfish and other sea life, and a tail that was only barely seen. The accompanying illustration provided by James Bingham depicts the creature with a build similar to bipedal theropod dinosaurs and a long crocodilian-like tail.

In The Beast from 20,000 Fathoms, the Rhedosaurus has a quadrupedal build, with a long tail and forelimbs noticeably longer than its hindlimbs. Its back is adorned with a single row of backward-facing spikes that continue from its scalp to its tail. Crocodilian scales line down its underside while bumpy, pebble-like scales cover the remainder of the body. Its snout is short with large nostrils and prominent fangs.

In Planet of Dinosaurs, the Rhedosaurus has a slimmer skull and a slightly longer neck. Its skin is brown.

In Ray Bradbury Comics #3, the sea monster is depicted as being some kind of plesiosaur specifically resembling Elasmosaurus with large pupil-less black eyes. The text refers to its having webbed fingers, despite the art clearly depicting it with flippers.


In The Beast from 20,000 Fathoms, the Rhedosaurus was the only surviving member of its species, buried beneath the ice in the Arctic for over 100 million years until it was reawakened by a nuclear bomb test in the modern day.

In Planet of Dinosaurs, the Rhedosaurus is an inhabitant of an alien planet identical to Earth in the Mesozoic era.


The Beast from 20,000 Fathoms

The United States conducted an atomic bomb test, known as "Operation Experiment", in the far north of the Arctic Circle. Shortly after the test was conducted, two men briefly noticed a 500-ton silhouette on the radar display and one of them informed Colonel Jack Evans. Tom Nesbitt and George Ritchie embarked on patrol at Post 18 around where the blast happened; Ritchie saw the creature and fell into a crevasse in shock. As soon as Nesbitt found him injured, the prehistoric monster created an avalanche from the glaciers above them. This trapped Ritchie in the crevasse, killing him. Nesbitt survived and was taken to a hospital in New York City, where he tried to convince Dr. Ingersoll that he truly saw a monster. Dr. Ingersoll and Evans disputed his claims. The latter informed Nesbitt that he went to the area afterward and saw no traces of the creature whatsoever.

Meanwhile, the dinosaur was heading toward the U.S., destroying a fishing boat near the Grand Banks. While still in the hospital ward, Nesbitt saw that the sole survivor reported this in a newspaper article. He went to a university's Department of Paleontology to meet Dr. Thurgood Elson, requesting that he start an expedition to search for the creature. However, Elson stated that he "can't support" his claim that an over 100-million-year-old prehistoric creature was awakened by the bomb and roams the sea. It was publicly announced that a second ship had been destroyed near Nova Scotia, Canada. The following day, Nesbitt returned to his office and received a visit from Elson's assistant, Dr. Lee Hunter, who had gathered illustrations of prehistoric creatures to help him identify what he saw in the Arctic. Nesbitt brought a sailor who witnessed the creature sink a ship to New York and the man also identified the same drawing as the monster. Elson then explained that it must be a Rhedosaurus, the only known fossils of which were found in the Hudson cliffs of the Hudson River 150 miles from New York. Elson asked Evans to report any more Rhedosaurus sightings to him, Hunter, and Nesbitt.

On one stormy night, the Rhedosaurus destroyed a lighthouse off the coast of Maine, killing two men inside. Soon after, Evan's friend Captain Phillip Jackson reported to the group that several buildings were destroyed by the creature along the Massachusetts coastline. A farmer was crushed to death. Elson then listed all of the sightings of the dinosaur, stating that it has followed the Arctic Current to the United States and that it is likely heading toward the canyon near New York where the only known fossils of its kind were found. Elson suggested that the Rhedosaurus should be captured, and desired to see it in person to determine what method to use. He asked Jackson for a diving bell to see the beast under a 150-mile undersea canyon, where it ultimately killed him.

The Rhedosaurus emerged in New York Harbor and wandered into downtown New York. Civilians fled in fear after it ate a policeman and destroyed cars in its path. The New York City Police Department dispatched their entire force to contain the Rhedosaurus and a group of officers fired rounds at the creature without effect. The creature then burst through a building and killed civilians behind it. Later that day, it was reported that the beast caused $300 million in damage, killed at least 180 civilians, and injured 1500 more.

That night, the United States Army prepared for the beast, setting up machine guns on rooftops and an electrified fence. The Rhedosaurus soon appeared and was shot in the neck by a bazooka while unsuccessfully trying to strike the fence; it strolled away and soldiers found blood from the creature, indicating that the bazooka successfully harmed it. Several troops followed the Rhedosaurus's blood trail when suddenly some collapsed; doctors soon discovered that they have been stricken by a deadly ancient disease it carried that was transmitted to them by its blood.

Meanwhile, the Rhedosaurus had returned to New York Bay, briefly remaining there before coming ashore on Manhattan Beach. Nesbitt told Evans that the only way to defeat the beast was to shoot a radionuclide into its tissue. As the Rhedosaurus ruined the rollercoaster on Coney Island, the army prepared the radioactive isotope. Nesbitt and sniper Corporal Stone travel to a high section of the rollercoaster and the latter fired the only radionuclide into the wound on its neck, both fatally wounding the beast and neutralizing the disease. As the Rhedosaurus succumbed to the isotope, a fire it started by destroying the machinery of a roller coaster spread across the island. The Rhedosaurus burst free of the burning coaster and roared out defiantly, before finally collapsing to the ground, dead.

Planet of Dinosaurs

The Rhedosaurus in Planet of Dinosaurs

As a Tyrannosaurus rex began menacing Captain Lee's crew, Lee and Jim broke into an argument over who should be in charge of crafting a plan to kill it. To prove his resolve, Lee baited the Tyrannosaurus into chasing him away from the camp when the trap preparations were not yet ready. As he continued to run, he took shelter under a ledge, above which a car-sized Rhedosaurus appeared. It hissed at Lee but did not chase him as he continued running. The pursuing Tyrannosaurus came upon the Rhedosaurus and roared at it. The Rhedosaurus roared back, prompting the Tyrannosaurus to lunge at it and bite it on the shoulder, carrying it in the air for several seconds as the Rhedosaurus struggled and tried to fight back. The conflict was ended when the Tyrannosaurus set the Rhedosaurus on the ground and quickly bit into its head, crushing its skull and killing it before carrying the body back to its lair to feed on it, giving Lee enough time to return to his crew and plan the counterattack against the dinosaur.


Contaminated blood

The Rhedosaurus's blood is host to a prehistoric virus. As the human immune system has no basis to defend against it, anyone exposed to it becomes fatally ill, including some soldiers who followed the trail of blood left by the creature after it was directly hit in the neck by a bazooka and forced to flee. Consequently, the U.S. military was forced to rule out heavy ordinance in their campaign against it.

Physical abilities

The Rhedosaurus primarily relies on its sheer bulk and powerful limbs during combat, shown when it topples over a lighthouse and crushes a car like it was an insect underneath its metaphorical boot. Its jaws were able to kill and eat a human in one bite as well.


The Rhedosaurus's scales were thick enough to be unharmed by bullets, though heavier munitions were able to wound it.


In The Beast from 20,000 Fathoms, it was evidently immune to most modern weaponry, as it ignored ammunition. Nevertheless, it was severely impaired by a shoulder-fired rocket shot into its neck, leaving a trail of contaminated blood behind. After Tom Nesbitt determined that the only way to kill the Rhedosaurus was with a radioactive isotope shot into its wounded neck, he and a sniper traveled to the heights of the roller coaster on Coney Island and shoot the isotope directly into its neck tissue, which caused the creature to collapse and die. In Planet of Dinosaurs, the Rhedosaurus was slain by a strong bite in the skull by a Tyrannosaurus rex.

Short stories

"The Fog Horn"

In the short story "The Fog Horn", which was adapted as The Beast from 20,000 Fathoms, a large, dinosaur-like creature with a longer neck, but otherwise similar to the Rhedosaurus, appears from the depths, attracted to a lighthouse and the sound of its fog horn. The creature first appeared circling the lighthouse, but left soon after. Exactly one year later, the creature reappeared and started calling out to the lighthouse. When the fog horn stopped calling back, the creature attacked and destroyed the lighthouse, then went back into the ocean, never to return.


"The Fog Horn"

One night per year, a mysterious sea beast came to the stone tower housing the fog light and fog horn operated by a man named McDunn. McDunn's assistant Johnny could not believe his eyes as the creature, unchanged for millions of years, arose on its 40-foot neck and roared at the tower. The fog horn roared back, and the beast returned the favor, while McDunn lamented the fact that while it was living its life the same as it ever did, the world it inhabited had changed around it in ways it could not possibly understand. He imagined that all year long it waited, and spent months surfacing to avoid damaging itself before swimming for days to get to the tower just to hear a familiar roar like its own. After the two exchanged another volley of bellowing, McDunn switched off the horn just to see what might happen. The beast stopped for a moment and growled at the tower. Angry with the lack of reply, it reared up and slammed into the tower. McDunn turned the horn back on, but it was too late. It bit at the light, shattering its glass casing, and leaned on the tower until it toppled over and the horn stopped sounding. Anguished at the realization that it had lost its only companion, the beast cried out intermittently all night, but was gone in the morning. McDunn told no one of what happened, blaming the damage on the waves, and the next year, Johnny came to visit McDunn in the new lighthouse erected on the same spot, but the creature never returned.


Main article: Rhedosaurus/Gallery.

In other languages

Language Name Meaning
Flagicon Japan.png Japanese リドサウルス Ridosaurusu Transcription of English name
Flagicon Portugal.png Portuguese Rhedossauro Adapted from English name, Portuguese -ssauro in place of -saurus
Flagicon Spain.png Spanish Rhedosaurio Adapted from English name, Spanish -saurio in place of -saurus


Since his first onscreen appearance in 1953, the Rhedosaurus has earned a reputation as an iconic and influential character in the monster genre, responsible for launching the formula of a giant monster unleashed by humanity's abuse of atomic weapons.[17][18] This is attributed to Ray Harryhausen's portrayal of the creature via stop-motion animation, in which he gave it persona and a memorable reptilian design.[19][18] Nevertheless, his representation of the dinosaur is also regarded as one of the most inaccurate in cinematic history.[20]

The Rhedosaurus and the dinosaur from "The Fog Horn" have been referenced or featured in various media throughout the years. In 1970, Harryhausen's protégé Jim Danforth purportedly paid homage to his mentor's work by briefly featuring a creature resembling the Rhedosaurus in the film When Dinosaurs Ruled the Earth.[21] Footage of the beast attacking New York City is briefly watched by two Gremlins in the 1990 film Gremlins 2: The New Batch (1990), and actor Colin Mochrie pretends to be reporting on the creature's attack without knowing what exactly is being projected through stock footage on the green screen behind him in the sixth episode of the second season of the ABC TV improvisational series Whose Line Is It Anyway?, which aired on October 14, 1999. A postcard featuring a screenshot of the Rhedosaurus from The Beast from 20,000 Fathoms is displayed in the background during the It's Always Sunny in Philadelphia episode "Mac's Mom Burns Her House Down" (episode 6 of season 6; originally aired on October 21, 2010). The scene where a giant Dragonite is attracted to a lighthouse horn scene in the thirteenth episode of Pokémon, entitled "Mystery at the Lighthouse", was inspired by the sea monster in "The Fog Horn". Director Daisuke Sato created a version of the sea monster from "The Fog Horn" for an unreleased 2007 short film of the same name.[22] The story would also later inspire his 2019 short Howl from Beyond the Fog.[23]

Artists have also made references to the Rhedosaurus in media such as comics and trading cards. The first was published as far back as December 1956, when a giant reptilian monster named Bodonga appeared in the third story of DC Comics' issue #104, which was titled "The Creature from 20,000 Fathoms!". A dinosaur modeled on the Rhedosaurus appears in issues #2 and 4 of the 2013 5-issue comic book miniseries Dinosaurs Attack! by IDW Publishing. In issue #2, after manifesting in Italy, it battles a dinosaur modeled on the Paleosaurus from The Giant Behemoth (which also manifests in the same area) at the Leaning Tower of Pisa, where it is shoved through the tower by its rival. In issue #4, it appears alongside several creatures as part of a charge against the U.S. military forces, with some of them resembling dinosaurian characters such as Godzilla (who leads the charge), Anguirus, Rodan, the Paleosaurus, Gorgo, Reptilicus, and Gertie the Dinosaur, among others.[24] The Rhedosaurus also appears together with the Paleosaurus in card #10 (of 55) of the Topps trading card series Dinosaurs Attack! (which was the basis for the above-mentioned miniseries), "Italy Under Seige [sic]!". The two dinosaurs are shown fighting each other at the Leaning Tower of Pisa in Italy.

The Rhedosaurus, along with King Kong, was notably one of the main inspirations for Godzilla. During the preproduction of the 1954 film Godzilla, its pre-published storyline was very similar to that of The Beast from 20,000 Fathoms and was actually titled The Giant Monster from 20,000 Miles Under the Sea (海底二万哩から来た大怪獣,   Kaiteinimanmairu kara Kita Daikaijū).[25] Rhedosaurus creator Ray Harryhausen personally considered Godzilla to be a "filch" of his own work.[26] In addition, Gamera shows evidence of inspiration from The Beast from 20,000 Fathoms and its titular creature.[27] Like the Rhedosaurus, Gamera slumbers in the Arctic in his debut film and is awakened by a nuclear explosion released by an aircraft. The company behind that film, Daiei, had distributed The Beast from 20,000 Fathoms to Japanese theaters a few weeks after the original 1954 Godzilla began distribution in the country.[28]


In The Beast from 20,000 Fathoms, the Rhedosaurus's roars are derived from the sound effects of a wild horse used in the 1952 film The Lion and the Horse.[29] The Rhedosaurus's main roars were reused for Harryhausen's dinosaurs in The Animal World (1956),[30] including the Triceratops.[31]

In the short story "The Fog Horn", its roar is said to be like the sound of a lighthouse's fog horn.

The Rhedosaurus's roars


  • Prior to the decision that the creature should be a giant dinosaur, the title monster was planned to be a giant octopus;[12][7] Ray Harryhausen later created such a creature for the 1955 film It Came from Beneath the Sea.[7] Godzilla co-creator Eiji Tsuburaya had converted the idea of a destructive giant octopus which foreshadowed the concept of It Came from Beneath the Sea several years before that film and Godzilla began development, and, like with Harryhausen and It Came from Beneath the Sea,[32] he eventually depicted a giant octopus in a film.
  • The Rhedosaurus is featured in posters for the 1953 3D science-fiction film Robot Monster, which was released to American theaters on June 10, three days before The Beast from 20,000 Fathoms was released.
  • Warner Bros.' advertising department evidently intended Godzilla to resemble the Rhedosaurus in its theatrical release posters for Gigantis the Fire Monster (1959).[33]

See also


  1. When explaining to the press why a fictional dinosaur was used in the film instead of an existing one, Eugène Lourié declared that the Rhedosaurus's height was 40 feet.[4] Its height has also been listed as being four stories,[5] or 50 feet.[6]


This is a list of references for Rhedosaurus. These citations are used to identify the reliable sources on which this article is based. These references appear inside articles in the form of superscript numbers, which look like this: [1]

  1. 1.0 1.1 1.2 1.3 Webber 2004, p. 50
  2. 2.0 2.1 Hankin 2008, p. 76
  3. "原子怪獣現わる [DVD]". Amazon. Retrieved 7 November 2021.
  4. Lansing State Journal 1953, p. 49.
  5. 5.0 5.1 News Journal 1953, p. 28
  6. Dayton Daily News 2008, p. 77
  7. 7.0 7.1 7.2 7.3 7.4 7.5 7.6 7.7 Harryhausen & Dalton 2006, p. 74
  8. Harryhausen & Dalton 2003, p. 49.
  9. Bradbury intro venice coaster.jpg
  10. "1946 Roller Coaster Database". Roller Coaster DataBase. Retrieved 18 June 2023.
  11. "Venice, California local history". westland.net. Retrieved 18 June 2023.
  12. 12.0 12.1 12.2 12.3 12.4 12.5 12.6 12.7 12.8 Hankin 2008, p. 76.
  13. Berry 2005, p. 36.
  14. Webber 2004, p. 52.
  15. Berry 2005, p. 33.
  16. 16.0 16.1 Harryhausen & Dalton 2008, p. 190.
  17. Bressan, David (16 July 2012). "Dinosaurs of the Atomic Age!". Scientific American. Retrieved 2 July 2023.
  18. 18.0 18.1 "The 50 Best Monster Movies of All Time". Paste. 12 May 2023. Retrieved 2 July 2023.
  19. Oosthuizen, Megan (9 February 2023). "The 21 Best Monster Movies Of All Time, Ranked". Fortress of Solitude. Retrieved 2 July 2023.
  20. Boyer, Daniel (25 March 2023). "10 Most Iconic Dinosaur Movie Characters". Collider. Retrieved 2 July 2023.
  21. Tamura 2021, p. 68.
  22. Hood, Robert (14 October 2009). "New Daikaiju Appears Through a Fog of Obscurity". Undead Backbrain. Archived from the original on 23 January 2021.
  23. Sato, Daisuke. "Keizo Murase is Back! Monster suit production campaign!". Kickstarter. Retrieved 18 June 2023.
  24. Dinosaurs Attack Homages.jpg
  25. Kabuki 1998, p. 34-38
  26. Shaw, William (20 November 2005). "The Origin of the Species". The Guardian. Retrieved 9 December 2021.
  27. Iwanami Shoten 1990, p. 151.
  28. The Beast from 20,000 Fathoms Poster 1.jpg
  29. Neuhaus, Lederman & Zito 1998, p. 53.
  30. Webber 2004, p. 100.
  31. Webber 2004, p. 95.
  32. Ragone 2014, p. 34.
  33. Ragone 2014, p. 47.


  • Webber, Ray P. (2004). The Dinosaur Films of Ray Harryhausen: Features, Early 16mm Experiments and Unrealized Projects. McFarland & Company. ISBN 978-0786416660.
  • Hankin, Mike (14 September 2008). Ray Harryhausen - Master of the Majicks Vol. 2: The American Films. Archive Editions, LLC. ISBN 978-0981782904.
  • "Monster, Mystery and Action Films Showing at Local Theaters". Lansing State Journal. 21 June 1953. p. 49.
  • News Journal. 28 June 1953. p. 28. Missing or empty |title= (help)
  • "Supersized Superstars". Dayton Daily News. 18 January 2008. p. 77.
  • Harryhausen, Ray; Dalton, Tony (2006). The Art of Ray Harryhausen. Billboard Books. ISBN 978-0823084005.
  • Harryhausen, Ray; Dalton, Tony (22 November 2003). Ray Harryhausen: An Animated Life. Aurum Press. ISBN 978-1854109408.
  • Berry, Mark F. (16 August 2005). The Dinosaur Filmography. McFarland & Company, Inc., Publishers. ISBN 978-0786424535.


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