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Species Profile

Amphicoelias Fragillimus

Maraapunisaurus fragillimus

The lost giant of the Morrison
E.D. Cope/Public Domain

Amphicoelias Fragillimus Distribution

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Endemic Species
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Found in 1 state/province

Size Comparison

Human 5'8"
Amphicoelias Fragillimus 32 ft 10 in

Amphicoelias Fragillimus is 5.8x the height of an average human.

Amphicoelias fragillus

At a Glance

Wild Species
Diet Herbivore
Activity Cathemeral
Lifespan 50 years
Weight 120000 lbs
Status Not Evaluated
Did You Know?

The entire species is based on a single, fragmentary dorsal vertebra described in 1878-and the original fossil was later lost, leaving only notes and a sketch (Cope, 1878).

Scientific Classification

A highly controversial and poorly known sauropod dinosaur from the Late Jurassic Morrison Formation of North America, famous for claims of extreme size based on a fragmentary, now-lost vertebral element. Originally described as Amphicoelias fragillimus and later reassigned to the genus Maraapunisaurus; both its exact relationships and size remain uncertain.

Kingdom
Animalia
Phylum
Chordata
Class
Reptilia
Order
Saurischia
Family
Rebbachisauridae
Genus
Maraapunisaurus
Species
Maraapunisaurus fragillimus

Distinguishing Features

  • Known (historically) from very fragmentary remains; diagnostic traits are debated
  • Often discussed as a possible gigantic sauropod, though size estimates are highly speculative
  • Currently commonly placed in Rebbachisauridae under the genus Maraapunisaurus (uncertain)

Physical Measurements

Height
32 ft 10 in (22 ft 12 in – 49 ft 3 in)
Length
131 ft 3 in (98 ft 5 in – 196 ft 10 in)
Weight
55.1 tons (22.0 tons – 132.3 tons)
Tail Length
65 ft 7 in (49 ft 3 in – 98 ft 5 in)
Top Speed
7 mph
About 12 km/h

Appearance

Primary Colors
Secondary Colors
Skin Type Maraapunisaurus fragillimus likely had no feathers, with thick, pebbly scales and possible larger scutes or plates along the back and neck, based on sauropod biology, not direct skin evidence.
Distinctive Features
  • Name history and uncertainty shape its 'appearance': first called Amphicoelias fragillimus from the Late Jurassic Morrison Formation, later renamed Maraapunisaurus fragillimus; relationships and size are disputed because the type fossils are lost.
  • Maraapunisaurus fragillimus is known only from one fragment of a large vertebra (not available now), so the animal's external features—head, neck, tail, and limb proportions—cannot be described with confidence.
  • Maraapunisaurus fragillimus is thought to have had a typical sauropod body: very large, four-legged plant-eater with a long neck and tail, small head, and pillar-like limbs; detailed reconstructions are hypothetical.
  • If Carpenter (2018) is right putting it in Rebbachisauridae, artists often show a diplodocoid-like shape—long body and tail and lighter than brachiosaurids, but this is a guess not backed by fossils.
  • Behavioral/life-history specifics (lifespan, herd structure, display features) are not recoverable for this species from existing material; only broad sauropod-typical ecology (large herbivore on Morrison floodplains) can be cautiously inferred without pretending precise measurements are known.

Did You Know?

The entire species is based on a single, fragmentary dorsal vertebra described in 1878-and the original fossil was later lost, leaving only notes and a sketch (Cope, 1878).

It was first named Amphicoelias fragillimus by Edward D. Cope during the Bone Wars era of American paleontology (Cope, 1878).

In 2018 it was reassigned to a new genus, Maraapunisaurus, and argued to be closer to rebbachisaurid diplodocoids than to Amphicoelias proper (Carpenter, 2018).

The species epithet fragillimus is Latin for "most fragile," reflecting Cope's description of the delicate, thin-walled bone.

Its fame largely comes from extreme size claims-but all such body-size estimates are indirect because the type specimen no longer exists for re-measurement.

If Carpenter's rebbachisaurid interpretation is correct, it would represent one of the geologically older and largest-bodied members proposed for that group (Carpenter, 2018).

Unique Adaptations

  • Type material indicates an extremely tall neural arch/spine region was reported for the dorsal vertebra; Cope's published account gives the only direct measurement record, but the specimen is lost and cannot be verified today (Cope, 1878).
  • Sauropod vertebrae commonly show extensive pneumaticity (air-filled chambers) that reduces mass; the reported "fragile" construction of the vertebra is consistent with this broader sauropod adaptation, though details for this species cannot be rechecked.
  • If correctly placed in Rebbachisauridae (Carpenter, 2018), it may have had rebbachisaurid-style back/torso anatomy (often with tall neural spines in the group), but the species currently lacks diagnostic skeletal coverage beyond the disputed vertebra.
  • Gigantism itself (if the animal was truly very large) would be an ecological adaptation for predator deterrence and long-range foraging efficiency, but size is the central uncertainty for this taxon.

Interesting Behaviors

  • Unknown for this species (no trackways, multiple skeletons, or gut contents are known).
  • Very likely an herbivore, as with other sauropods, using bulk-feeding and fermentation to process tough Jurassic vegetation (inferred from sauropod biology; not directly evidenced for this taxon).
  • Likely spent most time walking and browsing quadrupedally; rearing, herding, migration, and parental care are plausible sauropod behaviors but are not specifically documented for Maraapunisaurus fragillimus.
  • Would have relied on long-distance movement between feeding areas typical of large-bodied herbivores; any seasonal behavior is speculative without site data.

Cultural Significance

Maraapunisaurus fragillimus is a famous dinosaur known from a lost fossil. Its name and size estimates changed, causing debate. It shows how science updates ideas and why we must recheck original specimens and big "largest dinosaur" claims.

Myths & Legends

Bone Wars lore: Maraapunisaurus fragillimus (formerly Amphicoelias fragillimus) is tied to a missing giant vertebra from Cope's era in North American paleontology, known only from a sketch and few measurements.

Naming story as cultural association: "fragillimus" ("most fragile") enshrined, in name form, the dramatic impression the fossil made-so the dinosaur's identity is partly a legend of delicacy and enormity preserved in Latin rather than bone.

Maraapunisaurus fragillimus (formerly Amphicoelias fragillimus) became a nearly mythical giant sauropod in late-20th/early-21st dinosaur culture, often shown at impossible lengths and changing with each retelling because evidence is uncertain.

Conservation Status

NE Not Evaluated

Has not yet been evaluated against the criteria.

Population Unknown

Life Cycle

Lifespan 50 years

Lifespan

In the Wild
20–80 years

Reproduction

Mating System Data Deficient
Social Structure Transient
Breeding Pattern Seasonal
Fertilization Internal Fertilization
Birth Type Internal_fertilization

No direct evidence exists for the mating system of Maraapunisaurus fragillimus. Based on a fragmentary, now-lost specimen, internal fertilization is guessed. Mating likely involved brief encounters and seasonal breeding, but these traits are not proven.

Behavior & Ecology

Social Herd Group: 8
Activity Cathemeral
Diet Herbivore

Temperament

Unknown for this species (behavior cannot be directly recovered from the lost holotype and fragmentary record).
Unknown (no direct evidence for temperament or within-group aggression in Maraapunisaurus; behavior cannot be reliably determined from the available fossil material).
Unknown; no direct evidence preserves social temperament for Maraapunisaurus. As a very large sauropod herbivore, it was likely generally non-aggressive but capable of defensive behavior if threatened (specific displays or group behavior are not known).

Communication

Unknown for Maraapunisaurus fragillimus No direct anatomical correlates preserved
Based on sauropod-wide inference: likely produced low-frequency vocalizations (for example, rumbles/booms) and broadband sounds (hisses/exhalation sounds) generated via the respiratory tract; any infrasound-specific claims remain speculative.
Unknown Communication methods are not directly evidenced for this species, which is known from extremely fragmentary material
Substrate-borne signaling (foot stomps/ground vibrations) is plausible for very large-bodied animals but is not demonstrable for this species.
Chemical cues (feces/urine scent marking) are possible but untestable in the fossil record for this taxon.

Habitat

Biomes:
Temperate Forest Freshwater Wetland
Terrain:
Plains Valley Riverine
Elevation: Up to 4921 ft 3 in

Ecological Role

Large-bodied primary consumer (megaherbivore) in Late Jurassic Morrison Formation ecosystems; vegetation modifier and nutrient cycler.

High-volume herbivory shaping plant community structure (browsing/grazing pressure) Nutrient redistribution via dung and carcasses, enhancing soil fertility Physical disturbance of vegetation and soils via trampling, potentially influencing plant regeneration patterns Creation of feeding pathways/open patches that can increase habitat heterogeneity for smaller animals

Diet Details

Other Foods:
Conifer foliage and shoots Ginkgo leaves Cycad and bennettitalean foliage Fern fronds Horsetails

Human Interaction

Domestication Status

Wild

Maraapunisaurus fragillimus (formerly Amphicoelias fragillimus) is an extinct, non‑avian dinosaur from the Late Jurassic Morrison Formation of North America, known from one lost, fragmentary vertebral spine. Most traits (size, mass, behavior) are unknown; only E. D. Cope's 1878 spine height was recorded and led to varied whole‑body size estimates. No domestication history; humans interact via fossils.

As a Pet

Not Suitable as Pet

Legality: Maraapunisaurus fragillimus is not legal as a pet because it is extinct and cannot be kept alive. Any fossils would be covered by fossil or antiquities laws that vary by place (public land rules, permits, export limits).

Care Level: Expert Only

Purchase Cost:
Lifetime Cost:

Economic Value

Uses:
Scientific research (taxonomy, biomechanics, paleoecology) Museum exhibition and education Geoheritage/tourism tied to Morrison Formation sites Publishing/media/entertainment value driven by 'largest dinosaur' claims (potentially) commercial fossil trade-though no verified purchasable material for this species is known
Products:
  • peer-reviewed papers and taxonomic revisions (e.g., original description as Amphicoelias fragillimus by Cope, 1878; later reassignment to Maraapunisaurus)
  • museum exhibits/replicas and educational materials about sauropods and the Morrison Formation
  • documentaries/books/articles using Maraapunisaurus/'Amphicoelias fragillimus' as a case study in fragmentary evidence and size estimation

Relationships

Predators 4

Allosaurus
Allosaurus Allosaurus fragilis
Torvosaurus Torvosaurus tanneri
Ceratosaurus
Ceratosaurus Ceratosaurus nasicornis
Marshosaurus Marshosaurus bicentesimus

Related Species 5

Rebbachisaurus Rebbachisaurus garasbae Shared Family
Nigersaurus Nigersaurus taqueti Shared Family
Limaysaurus Limaysaurus tessonei Shared Family
Demandasaurus Demandasaurus darwini Shared Family
Zapalasaurus Zapalasaurus bonapartei Shared Family

Ecological Equivalents 5

Animals that fill a similar ecological role in their ecosystem

Diplodocus
Diplodocus Diplodocus carnegii Large-bodied Morrison Formation sauropod herbivore that likely overlapped in habitat and plant resources; commonly used as a baseline for scaling fragmentary diplodocoid material.
Apatosaurus Apatosaurus louisae Co-occurring Morrison megaherbivore. Occupies a similar broad niche as a high-biomass browser/grazer, with predator deterrence inferred via large body size and tail/whip-like defenses characteristic of diplodocoids.
Supersaurus
Supersaurus Supersaurus vivianae Another very large Morrison diplodocoid. Ecological comparison is common because Maraapunisaurus was historically interpreted as an extreme-size, diplodocid-like animal based on a tall posterior dorsal neural arch.
Camarasaurus Camarasaurus lentus Abundant Morrison sauropod. Overlaps as a megaherbivore but likely differed in feeding mechanics and feeding height, and in skull-and-tooth morphology (broader-snouted macronarian versus diplodocoid-type feeding), making it a useful ecological contrast.
Brachiosaurus
Brachiosaurus Brachiosaurus altithorax Sympatric Morrison Formation megaherbivore used as a high-browsing niche comparator; contrasts likely feeding height and center of mass with diplodocoid- and rebbachisaurid-style forms.

“The Amphicoelias fragillimus had no natural predators due to its enormous size.”

Summary

The Amphicoelias fragillimus was among the largest dinosaurs that ever lived. This giant Sauropod lived 140 to 160 million years ago during the Jurassic period. Its fossils were found in Colorado. The Amphicoelias fragillimus was an herbivore that used its extraordinarily long neck to eat leaves from high trees in forests and grasslands. This species is identified from a single fossil specimen, so the size estimates of this animal have varied immensely over the years. Although only a single fossil was found, this fossil is estimated to be the largest dinosaur specimen ever discovered.

Scientific Name

Amphicoelias fragillimus

The name Amphicoelias fragillimus can be divided into two parts: Amphicoelias means “double hollow” and refers to the thin walls of the animal’s vertebrae. This adaptation occurred so that the huge dinosaur could easily support its large skeleton. Fragillimus literally means “fragile,” owing to how thin all the bones were. This species was named by Edward Drinker Cope, a paleontologist who found the initial samples of the animal in 1877. The Amphicoelias fragillimus is closely related to other giant Sauropods, most notably the Diplodocus.

Description & Size

The Amphicoelias fragillimus was a massive animal with a long neck, short legs, and an extended tail. Considering the dinosaur’s size, it weighed much less than you would think due to its thin, hollow bones. Outwardly, these animals are thought to have had scaly, brown skin and a small head in comparison to the rest of their body. Their physical features were as follows:

Length130-200 ft
Single vertebral Length5-8 ft
Weight200,000 to 300,000 lbs
Neck Length45-60 ft

To put their length into perspective, it would take you around 80 footsteps to walk the length of the average Amphicoelias fragillimus. In terms of weight, it was around two-thirds that of a blue whale.

Amphicoelias skeleton 1892

The Amphicoelias fragillimus was a massive animal with a long neck, short legs, and an extended tail.

Diet – What Did the Amphicoelias Fragillimus Eat?

The Amphicoelias fragillimus was an herbivore, meaning its diet was based solely on plants. They had a long and slow digestive system. And similar to other massive animals living today, such as elephants and giraffes, their slow digestion allowed them to eat less nutritious food and thrive on fewer calories than an animal of this size would otherwise need.

Since they lived in terrestrial areas of the United States, they fed on plants such as ferns and leaves as their primary diet. Other food sources include gingko, cycads, seed ferns, horsetails, and club mosses. This dietary analysis is entirely based on data gathered from fossils. Thus, their diet is entirely based on speculation, and we might discover something new in the future.

Habitat – When and Where It Lived?

The Amphicoelias fragillimus lived between the Kimmeridgian to Tithonian eras of the Jurassic period. This was roughly 145 to 160 million years ago. The habitat of these behemoths was likely a lush tropical savannah, covered in greenery for them to eat, a typical habitat for giant sauropods. Cope discovered the single fossil specimen in Garden Park, Colorado. This is the only confirmed location of the species, although it is likely it also lived in other regions.

Threats and Predators

As mentioned above, this gigantic diplodocid dinosaur belongs to a family of massive sauropods with long necks, thin bones, and huge bodies. Considering it was one of the largest dinosaurs during its time, the chances of other animals preying on it were rather slim. The only threat the animal possibly faced was climate change and other sauropod dinosaurs living in the same habitat, fighting over food and possible mates.

Discoveries and Fossils – Where It Was Found

The fossils of the Amphicoelias fragillimus were discovered in the Colorado mudstone in fragmented rock. Since the fossil evidence was only part of a single vertebra, paleontologists used a sketch to estimate the size and skeletal structure of the rest of the dinosaur. 

Unfortunately, the fossil disappeared very soon after its discovery, and only one scientist, Edward Drinker Cope, was able to study the specimen. All current size estimations and descriptions of the animal are based on the original sketch, study, and observations from Edward Drinker Cope made in 1877.

Extinction – When Did It Die Out?

The animal lived during the Late Jurassic period. Thus, it most likely went extinct during the Jurassic – Triassic extinction period. This was the most severe extinction event in natural history, during which 76 percent of all species on the planet died out. This occurred due to the rapidly changing temperatures and rising sea levels. These animals were likely not very adaptable to changing weather conditions due to their large size. 

Similar Animals to the Amphicoelias Fragillimus

Similar dinosaurs to the Amphicoelias fragillimus include: 

  • Patagotitan A large Sauropod native to Patagonia in modern-day Argentina. This animal was about the same size as the Amphicoelias framillimus.
  • Camarasaurus – A quadrupedal herbivore with almost the same weight as Amphicoelias fragillimus.
  • Argentiosaurus – A gigantic herbivore dinosaur, estimated to be the largest dinosaur ever, almost the same length as Amphicoelias fragillimus.
  • Supersaurus – Another large, herbivore sauropod from the North American region.
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Sources

  1. Prehistoric Wildlife / Accessed November 5, 2022
  2. Kid ADL / Accessed November 5, 2022
  3. Fossil Fandom / Accessed November 5, 2022
  4. All the Science / Accessed November 5, 2022
Lev Baker

About the Author

Lev Baker

Lev is a writer at AZ Animals who primarily covers topics on animals, geography, and plants. He has been writing for more than 4 years and loves researching topics and learning new things. His three biggest loves in the world are music, travel, and animals. He has his diving license and loves sea creatures. His favorite animal in the world is the manta ray.
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Amphicoelias Fragillimus FAQs (Frequently Asked Questions)

This giant Sauropod lived 140 to 160 million years ago during the Jurassic period.