Amphicoelias
Encyclopedia
Amphicoelias is a genus
of herbivorous sauropod dinosaur
that includes what may be the largest dinosaur
ever discovered, A. fragillimus. Based on surviving descriptions of a single fossil
bone, A. fragillimus may have been the longest known vertebrate
at 40 to 60 m (131.2 to 196.9 ft) in length, and may have had a mass of up to 122 metric tons (135 short ton
s). However, because the only fossil remains were lost at some point after being studied and described in the 1870s, evidence survives only in drawings and field notes. Amphicoelias is present in stratigraphic zone 6 of the Morrison Formation
.
in December 1877 (though not published until 1878) for an incomplete skeleton consisting of two vertebrae, a pubis
(hip bone), and a femur
(upper leg bone). Cope also named a second species, A. latus, in the same paper. However, all subsequent researchers have considered A. latus to be a synonym of A. altus. In 1921, Osborn and Mook assigned additional bones to A. altus—a scapula (shoulder blade), a coracoid (shoulder bone), an ulna (lower arm bone), and a tooth. Henry Fairfield Osborn
and Charles Craig Mook noted the overall close similarity between Amphicoelias and Diplodocus
, as well as a few key differences, such as proportionally longer forelimbs in Amphicoelias than in Diplodocus. The femur of Amphicoelias is unusually long, slender, and round in cross section; while this roundness was once thought to be another distinguishing characteristic of Amphicoelias, it has since been found in some specimens of Diplodocus as well. A. altus was also similar in size to Diplodocus, estimated to be about 25 m (82 ft) long. While most scientists have used these details to distinguish Amphicoelias and Diplodocus as separate genera, at least one (John Foster, in his 2007 book Jurassic West) has suggested that Amphicoelias is probably the senior synonym of Diplodocus.
The third named Amphicoelias species, A. fragillimus, is known only from a single, incomplete 1.5 m tall neural arch (the part of a vertebra with spines and processes), either last or second to last in the series of back vertebrae, D (dorsal) 10 or D9, that would have measured 2.7 m (8.8 ft) long in life. In addition to this single vertebra, Cope's field notes contain an entry for an "[i]mmense distal end of femur” located only a few tens of meters away from the giant vertebra, and it is likely that this undescribed leg bone belonged to the same individual animal as the neural spine.
In 2010, a monograph was made available, but not formally published, by Henry Galiano and Raimund Albersdorfer in which they referred a fourth species to Amphicoelias, as "A. brontodiplodocus" based on several complete specimens found in the Dana Quarry of Big Horn Basin, Wyoming and held in a private collection. The specific name referred to their hypothesis based on these specimens that nearly all Morrison diplodocid species are either growth stages or represent sexual dimorphism among members of the genus Amphicoelias, but this analysis has been met with skepticism and the publication itself has been disclaimed by its lead author, explaining that it is "obviously a drafted manuscript complete with typos, etc., and not a final paper. In fact, no printing or distribution has been attempted" (see comment on previous reference).
Amphicoelias fragillimus was collected by Oramel Lucas, a fossil collector employed by E.D. Cope, shortly after he was hired by Cope in 1877. Lucas discovered a partial vertebra (the neural arch and spine) of the new sauropod species in Garden Park, north of Cañon City, Colorado
, close to the quarry that yielded Camarasaurus
. The vertebra was in poor condition, but astonishingly large, measuring 1.5 metres (4.9 ft) up to 2.7 metres (8.9 ft) in height. Lucas shipped the specimen to Cope in the spring or early summer of 1878, and Cope published it as the holotype
specimen (catalogue number AMNH 5777) of a new species, A. fragillimus, that August. The name derives from the Latin
fragillimus ("very fragile"), referring to the delicateness of the bone produced by very thin laminae
(vertebral walls). As revealed in Cope's notebooks, which he recorded based on Lucas' report on excavation site locations in 1879, the specimen came from a hill south of the Camarasaurus quarry now known as "Cope's Nipple." While Cope originally wrote that the site belonged to the Dakota Formation
(mid-Cretaceous
in age), the presence of dinosaurs such as Camarasaurus
in the same rocks indicates that they probably belong to the Morrison Formation
, which places the age of the site at 150 million years ago in the late Jurassic
period, specifically the Tithonian
age. A gigantic fossilized femur was also recovered in close proximity to the vertebra, and may have belonged to A. fragilimus.
The gigantic bones attributed to A. fragillimus have often been ignored in summaries of the largest dinosaurs partly because, according to various subsequent reports, the whereabouts of both the vertebra and the femur
are unknown, and all attempts to locate them have failed. Carpenter, in 2006, presented a possible scenario for the disappearance of the A. fragillimus specimens. As Cope noted in his description, the neural arch bone material was very fragile, and techniques to harden and preserve fossil bone had not yet been invented (Cope's rival, paleontologist O.C. Marsh, was the first to use such chemicals, in the early 1880s). Carpenter observed that the fossil bones known from the A. fragillimus quarry would have been preserved in deeply weathered mudstone
, which tends to crumble easily and fragment into small, irregular cubes. Therefore, the bone may have crumbled badly and been discarded by Cope soon after he illustrated it in rear view for his paper (Carpenter suggested that this may explain why Cope drew the vertebra in only one view, rather than from multiple angles as he did for his other discoveries).
In 1994, an attempt was made to relocate the original quarry where A. fragillimus and other species had been found, using ground-penetrating radar
in an attempt to image bones still buried in the ground. This attempt failed because the fossilized mudstone bones were the same density as the surrounding rock, making it impossible to differentiate the two. A study of the local topography also showed that the fossil-bearing rock strata was severely eroded, and probably was so at the time Lucas made his discovery of A. fragillimus, indicating that a majority of the skeleton was gone by the time the vertebra and femur were recovered.
Carpenter (2006) also noted that, due to the extraordinary size and mysterious disappearance of the fossil, Cope's description of A. fragillimus has been met with skepticism, with some people assuming that there were typographical errors in his measurements. Carpenter argued that there is every reason to take Cope at his word, noting that the paleontologist's reputation was at stake. The discovery took place during the Bone Wars
, and Cope's rival Marsh, who was "ever ready to humiliate" Cope, never called the claims into question. Marsh was known to have employed spies to monitor Cope's discoveries, and may have even had confirmation of the enormous size of the Amphicoelias fragillimus bones. Paleontologists Henry Fairfield Osborn and C.C. Mook in 1921, as well as John S. McIntosh in 1998, also accepted Cope's data without question in published reviews.
Producing an estimate of the complete size of A. fragillimus requires scaling the bones of better known species of diplodocid (a family of extremely long and slender sauropods) in the assumption that their relative proportions were similar. In his original paper, Cope did this by speculating on the size of a hypothetical A. fragillimus femur (upper leg bone). Cope noticed that in other sauropod dinosaurs, specifically A. altus and Camarasaurus supremus
, the femora were always twice as tall as the tallest dorsal vertebra, and estimated the size of an A. fragillimus femur to be 12 ft (3.7 m) tall.
In 1994, using the related Diplodocus
as a reference, Gregory S. Paul
estimated a femur length of 3.1–4 m (10–13 ft) for A. fragillimus. The 2006 re-evaluation of A. fragillimus by Ken Carpenter also used Diplodocus as a scale guide, finding a femur height of 4.3–4.6 m (14–15 ft). Carpenter went on to estimate the complete size of A. fragillimus, though he cautioned that relative proportions in diplodocids could vary from species to species. Assuming the same proportions as the well-known Diplodocus, Carpenter presented an estimated total length of 58 m (190 ft), which he noted fell within the range presented by Paul in 1994 (40–60 m, or 131–196 ft). Carpenter pointed out that even the lowest length estimates for A. fragillimus were higher than those for other giant sauropods, such as the diplodocid Supersaurus
(32.5 m, 107 ft), the brachiosaurid Sauroposeidon
(34 m, 111 ft), and the titanosaur
Argentinosaurus
(30 m, 98 ft). Carpenter presented more speculative, specific proportions for A. fragillimus (again, based on a scaled-up Diplodocus), including a neck length of 16.75 m (55 ft), a body length of 9.25 m (30 ft), and a tail length of 32 m (105 ft). He estimated the total forelimb height at 5.75 m (19 ft) and hind limb height at 7.5 m (25 ft), and the overall height (at the highest point on the back) at 9.25 m (30 ft). By comparison the blue whale
, which is on average the longest living creature, reaches 30 m (98 ft) in length.
While A. fragillimus was relatively thin, its enormous size still made it very massive. Weight is much more difficult to determine than length in sauropods, as the more complex equations needed are prone to greater margins of error based on smaller variations in the overall proportions of the animal. Carpenter used Paul's 1994 estimate of the mass of Diplodocus carnegii (11.5 tons) to speculate that A. fragillimus could have weighed up to 122.4 metric tons. The heaviest blue whale
on record weighed about 195 tons, and the heaviest dinosaur known from reasonably good remains, the Argentinosaurus
, weighed 80–100 tons, although if the size estimates can be validated, it would still be lighter than Bruhathkayosaurus
, which is estimated to have weighed 139 tons.
Edward Drinker Cope described his finds in two 1878 issues of the American Naturalist
, and assigned them to the new genus
Amphicoelias. He placed it in a unique family, Amphicoeliidae, though this is now considered a nomen oblitum
(forgotten name). The genus is usually assigned to the family Diplodocidae, though some modern analyses have found it at the base of the larger group Diplodocoidea
or as a diplodocid incertae sedis (uncertain placement). The first named species in the genus, Amphicoelias altus (holotype
specimen AMHD 5764), was discovered by Cope in 1877. But while it is only represented by a partial skeleton, there are enough diagnostic characteristics to provisionally define the genus. A. altus is known from better remains, but is smaller than A. fragillimus. Cope also named a third species in 1878: Amphicoelias latus.
Osborn and Mook, in 1921, provisionally synonymized the three species, sinking A. latus into A. altus, and suggesting also that A. fragillimus is just a very large individual of A. altus, a position McIntosh agreed with in 1998. Carpenter (2006) disagreed about the synonymy of A. altus and A. fragillimus, however, citing numerous differences in the construction of the vertebra also noted by Cope, and suggested these differences are enough to warrant a separate species or even a separate genus for A. fragillimus. However, he went on to caution that the validity of A. fragillimus as a separate species is nearly impossible to determine without the original specimen to study.
In 2007, John Foster suggested that the differences usually cited to differentiate Amphicoelias altus from the more well known Diplodocus
are not significant and may be due to individual variation. Foster argued that Amphicoelias is probably the senior synonym of Diplodocus, and that if further research bears this out, the familiar name Diplodocus would need to be abandoned in favor of Amphicoelias, as was the case with Brontosaurus and its senior synonym Apatosaurus
.
Period, and concluded that whatever evolutionary pressure caused large size was present from the early origins of the group. Carpenter cited several studies of giant mammal
ian herbivores, such as elephant
s and rhinoceros
, which showed that larger size in plant-eating animals leads to greater efficiency in digesting food. Since larger animals have longer digestive systems, food is kept in digestion for significantly longer periods of time, allowing large animals to survive on lower-quality food sources. This is especially true of animals with a large number of 'fermentation chambers' along the intestine which allow microbes to accumulate and ferment plant material, aiding digestion. Throughout their evolutionary history, sauropod dinosaurs were found primarily in semi-arid, seasonally dry environments, with a corresponding seasonal drop in the quality of food during the dry season. The environment of Amphicoelias was essentially a savanna
, similar to the arid environments in which modern giant herbivores are found, supporting the idea that poor-quality food in an arid environment promotes the evolution of giant herbivores. Carpenter argued that other benefits of large size, such as relative immunity from predators, lower energy expenditure, and longer life span, are probably secondary advantages.
The Morrison Formation
environment in which Amphicoelias lived would have resembled a modern savanna, though since grass
did not appear until the Late Cretaceous
, fern
s were probably the dominant plant and main food source for Amphicoelias. Though Engelmann et al. (2004) dismissed ferns as a sauropod food source due to their relatively low caloric content, Carpenter argued that the sauropod digestive system, well adapted to handle low-quality food, allows for the consumption of ferns as a large part of the sauropod diet. Carpenter also noted that the occasional presence of large petrified logs indicate the presence of 20–30 m (65–100 ft) tall trees, which would seem to conflict with the savanna comparison. However, the trees are rare, and since tall trees require more water than the savanna environment could generally provide, they probably existed in narrow tracts or 'gallery forests' along rivers and gulleys where water could accumulate. Carpenter speculated that giant herbivores like Amphicoelias may have used the shade of the gallery forests to stay cool during the day, and done most of their feeding on the open savanna at night.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of herbivorous sauropod dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
that includes what may be the largest dinosaur
Dinosaur size
Size has been one of the most interesting aspects of dinosaur science to the general public. This article lists the largest and smallest dinosaurs from various groups, sorted in order of weight and length....
ever discovered, A. fragillimus. Based on surviving descriptions of a single fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
bone, A. fragillimus may have been the longest known vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
at 40 to 60 m (131.2 to 196.9 ft) in length, and may have had a mass of up to 122 metric tons (135 short ton
Short ton
The short ton is a unit of mass equal to . In the United States it is often called simply ton without distinguishing it from the metric ton or the long ton ; rather, the other two are specifically noted. There are, however, some U.S...
s). However, because the only fossil remains were lost at some point after being studied and described in the 1870s, evidence survives only in drawings and field notes. Amphicoelias is present in stratigraphic zone 6 of the Morrison Formation
Morrison Formation
The Morrison Formation is a distinctive sequence of Late Jurassic sedimentary rock that is found in the western United States, which has been the most fertile source of dinosaur fossils in North America. It is composed of mudstone, sandstone, siltstone and limestone and is light grey, greenish...
.
Description
The type species of Amphicoelias, A. altus, was named by paleontologist Edward Drinker CopeEdward Drinker Cope
Edward Drinker Cope was an American paleontologist and comparative anatomist, as well as a noted herpetologist and ichthyologist. Born to a wealthy Quaker family, Cope distinguished himself as a child prodigy interested in science; he published his first scientific paper at the age of nineteen...
in December 1877 (though not published until 1878) for an incomplete skeleton consisting of two vertebrae, a pubis
Pubis
Pubis may refer to:* Pubis * Mons pubis, a padding of fat that protects the pubis bone...
(hip bone), and a femur
Femur
The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...
(upper leg bone). Cope also named a second species, A. latus, in the same paper. However, all subsequent researchers have considered A. latus to be a synonym of A. altus. In 1921, Osborn and Mook assigned additional bones to A. altus—a scapula (shoulder blade), a coracoid (shoulder bone), an ulna (lower arm bone), and a tooth. Henry Fairfield Osborn
Henry Fairfield Osborn
Henry Fairfield Osborn, Sr. ForMemRS was an American geologist, paleontologist, and eugenicist.-Early life and career:...
and Charles Craig Mook noted the overall close similarity between Amphicoelias and Diplodocus
Diplodocus
Diplodocus , or )is a genus of diplodocid sauropod dinosaur whose fossils were first discovered in 1877 by S. W. Williston. The generic name, coined by Othniel Charles Marsh in 1878, is a Neo-Latin term derived from Greek "double" and "beam", in reference to its double-beamed chevron bones...
, as well as a few key differences, such as proportionally longer forelimbs in Amphicoelias than in Diplodocus. The femur of Amphicoelias is unusually long, slender, and round in cross section; while this roundness was once thought to be another distinguishing characteristic of Amphicoelias, it has since been found in some specimens of Diplodocus as well. A. altus was also similar in size to Diplodocus, estimated to be about 25 m (82 ft) long. While most scientists have used these details to distinguish Amphicoelias and Diplodocus as separate genera, at least one (John Foster, in his 2007 book Jurassic West) has suggested that Amphicoelias is probably the senior synonym of Diplodocus.
The third named Amphicoelias species, A. fragillimus, is known only from a single, incomplete 1.5 m tall neural arch (the part of a vertebra with spines and processes), either last or second to last in the series of back vertebrae, D (dorsal) 10 or D9, that would have measured 2.7 m (8.8 ft) long in life. In addition to this single vertebra, Cope's field notes contain an entry for an "[i]mmense distal end of femur” located only a few tens of meters away from the giant vertebra, and it is likely that this undescribed leg bone belonged to the same individual animal as the neural spine.
In 2010, a monograph was made available, but not formally published, by Henry Galiano and Raimund Albersdorfer in which they referred a fourth species to Amphicoelias, as "A. brontodiplodocus" based on several complete specimens found in the Dana Quarry of Big Horn Basin, Wyoming and held in a private collection. The specific name referred to their hypothesis based on these specimens that nearly all Morrison diplodocid species are either growth stages or represent sexual dimorphism among members of the genus Amphicoelias, but this analysis has been met with skepticism and the publication itself has been disclaimed by its lead author, explaining that it is "obviously a drafted manuscript complete with typos, etc., and not a final paper. In fact, no printing or distribution has been attempted" (see comment on previous reference).
History of A. fragillimus
Colorado
Colorado is a U.S. state that encompasses much of the Rocky Mountains as well as the northeastern portion of the Colorado Plateau and the western edge of the Great Plains...
, close to the quarry that yielded Camarasaurus
Camarasaurus
Camarasaurus meaning 'chambered lizard', referring to the hollow chambers in its vertebrae was a genus of quadrupedal, herbivorous dinosaurs. It was the most common of the giant sauropods to be found in North America...
. The vertebra was in poor condition, but astonishingly large, measuring 1.5 metres (4.9 ft) up to 2.7 metres (8.9 ft) in height. Lucas shipped the specimen to Cope in the spring or early summer of 1878, and Cope published it as the holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
specimen (catalogue number AMNH 5777) of a new species, A. fragillimus, that August. The name derives from the Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
fragillimus ("very fragile"), referring to the delicateness of the bone produced by very thin laminae
Lamina of the vertebral arch
The laminæ are two broad plates, extending dorsally and medially from the pedicles, fusing to complete the roof of the vertebral arch.Their upper borders and the lower parts of their anterior surfaces are rough for the attachment of the ligamenta flava....
(vertebral walls). As revealed in Cope's notebooks, which he recorded based on Lucas' report on excavation site locations in 1879, the specimen came from a hill south of the Camarasaurus quarry now known as "Cope's Nipple." While Cope originally wrote that the site belonged to the Dakota Formation
Dakota Formation
The Dakota Formation is a geologic formation composed of sedimentary rocks deposited on the western side of the Late Cretaceous Western Interior Seaway. F.B. Meek and F.V. Hayden named it for exposures along the Missouri River near Dakota City, Nebraska...
(mid-Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
in age), the presence of dinosaurs such as Camarasaurus
Camarasaurus
Camarasaurus meaning 'chambered lizard', referring to the hollow chambers in its vertebrae was a genus of quadrupedal, herbivorous dinosaurs. It was the most common of the giant sauropods to be found in North America...
in the same rocks indicates that they probably belong to the Morrison Formation
Morrison Formation
The Morrison Formation is a distinctive sequence of Late Jurassic sedimentary rock that is found in the western United States, which has been the most fertile source of dinosaur fossils in North America. It is composed of mudstone, sandstone, siltstone and limestone and is light grey, greenish...
, which places the age of the site at 150 million years ago in the late Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
period, specifically the Tithonian
Tithonian
In the geologic timescale the Tithonian is the latest age of the Late Jurassic epoch or the uppermost stage of the Upper Jurassic series. It spans the time between 150.8 ± 4 Ma and 145.5 ± 4 Ma...
age. A gigantic fossilized femur was also recovered in close proximity to the vertebra, and may have belonged to A. fragilimus.
Lost fossils
Femur
The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...
are unknown, and all attempts to locate them have failed. Carpenter, in 2006, presented a possible scenario for the disappearance of the A. fragillimus specimens. As Cope noted in his description, the neural arch bone material was very fragile, and techniques to harden and preserve fossil bone had not yet been invented (Cope's rival, paleontologist O.C. Marsh, was the first to use such chemicals, in the early 1880s). Carpenter observed that the fossil bones known from the A. fragillimus quarry would have been preserved in deeply weathered mudstone
Mudstone
Mudstone is a fine grained sedimentary rock whose original constituents were clays or muds. Grain size is up to 0.0625 mm with individual grains too small to be distinguished without a microscope. With increased pressure over time the platey clay minerals may become aligned, with the...
, which tends to crumble easily and fragment into small, irregular cubes. Therefore, the bone may have crumbled badly and been discarded by Cope soon after he illustrated it in rear view for his paper (Carpenter suggested that this may explain why Cope drew the vertebra in only one view, rather than from multiple angles as he did for his other discoveries).
In 1994, an attempt was made to relocate the original quarry where A. fragillimus and other species had been found, using ground-penetrating radar
Radar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...
in an attempt to image bones still buried in the ground. This attempt failed because the fossilized mudstone bones were the same density as the surrounding rock, making it impossible to differentiate the two. A study of the local topography also showed that the fossil-bearing rock strata was severely eroded, and probably was so at the time Lucas made his discovery of A. fragillimus, indicating that a majority of the skeleton was gone by the time the vertebra and femur were recovered.
Carpenter (2006) also noted that, due to the extraordinary size and mysterious disappearance of the fossil, Cope's description of A. fragillimus has been met with skepticism, with some people assuming that there were typographical errors in his measurements. Carpenter argued that there is every reason to take Cope at his word, noting that the paleontologist's reputation was at stake. The discovery took place during the Bone Wars
Bone Wars
The Bone Wars, also known as the "Great Dinosaur Rush", refers to a period of intense fossil speculation and discovery during the Gilded Age of American history, marked by a heated rivalry between Edward Drinker Cope and Othniel Charles Marsh...
, and Cope's rival Marsh, who was "ever ready to humiliate" Cope, never called the claims into question. Marsh was known to have employed spies to monitor Cope's discoveries, and may have even had confirmation of the enormous size of the Amphicoelias fragillimus bones. Paleontologists Henry Fairfield Osborn and C.C. Mook in 1921, as well as John S. McIntosh in 1998, also accepted Cope's data without question in published reviews.
Size
Camarasaurus
Camarasaurus meaning 'chambered lizard', referring to the hollow chambers in its vertebrae was a genus of quadrupedal, herbivorous dinosaurs. It was the most common of the giant sauropods to be found in North America...
, the femora were always twice as tall as the tallest dorsal vertebra, and estimated the size of an A. fragillimus femur to be 12 ft (3.7 m) tall.
In 1994, using the related Diplodocus
Diplodocus
Diplodocus , or )is a genus of diplodocid sauropod dinosaur whose fossils were first discovered in 1877 by S. W. Williston. The generic name, coined by Othniel Charles Marsh in 1878, is a Neo-Latin term derived from Greek "double" and "beam", in reference to its double-beamed chevron bones...
as a reference, Gregory S. Paul
Gregory S. Paul
Gregory Scott Paul is a freelance researcher, author and illustrator who works in paleontology, and more recently has examined sociology and theology. He is best known for his work and research on theropod dinosaurs and his detailed illustrations, both live and skeletal...
estimated a femur length of 3.1–4 m (10–13 ft) for A. fragillimus. The 2006 re-evaluation of A. fragillimus by Ken Carpenter also used Diplodocus as a scale guide, finding a femur height of 4.3–4.6 m (14–15 ft). Carpenter went on to estimate the complete size of A. fragillimus, though he cautioned that relative proportions in diplodocids could vary from species to species. Assuming the same proportions as the well-known Diplodocus, Carpenter presented an estimated total length of 58 m (190 ft), which he noted fell within the range presented by Paul in 1994 (40–60 m, or 131–196 ft). Carpenter pointed out that even the lowest length estimates for A. fragillimus were higher than those for other giant sauropods, such as the diplodocid Supersaurus
Supersaurus
Supersaurus is a genus of diplodocid sauropod dinosaur discovered by Vivian Jones of Delta, Colorado, in the Upper Jurassic Morrison Formation of Colorado in 1972. The fossil remains came from the Brushy Basin Member of the formation, dating to about 153 million years ago...
(32.5 m, 107 ft), the brachiosaurid Sauroposeidon
Sauroposeidon
Sauroposeidon is a genus of sauropod dinosaur known from four neck vertebrae that were found in the southeastern portion of the US state of Oklahoma. The fossils were found in rocks dating to the Early Cretaceous, a period when the sauropods of North America had diminished in both size and...
(34 m, 111 ft), and the titanosaur
Titanosaur
Titanosaurs were a diverse group of sauropod dinosaurs, which included Saltasaurus and Isisaurus. It includes some of the heaviest creatures ever to walk the earth, such as Argentinosaurus and Paralititan — which some believe have weighed up to 100 tonnes...
Argentinosaurus
Argentinosaurus
Argentinosaurus is a genus of titanosaur sauropod dinosaur first discovered by Guillermo Heredia in Argentina. The generic name refers to the country in which it was discovered...
(30 m, 98 ft). Carpenter presented more speculative, specific proportions for A. fragillimus (again, based on a scaled-up Diplodocus), including a neck length of 16.75 m (55 ft), a body length of 9.25 m (30 ft), and a tail length of 32 m (105 ft). He estimated the total forelimb height at 5.75 m (19 ft) and hind limb height at 7.5 m (25 ft), and the overall height (at the highest point on the back) at 9.25 m (30 ft). By comparison the blue whale
Blue Whale
The blue whale is a marine mammal belonging to the suborder of baleen whales . At in length and or more in weight, it is the largest known animal to have ever existed....
, which is on average the longest living creature, reaches 30 m (98 ft) in length.
While A. fragillimus was relatively thin, its enormous size still made it very massive. Weight is much more difficult to determine than length in sauropods, as the more complex equations needed are prone to greater margins of error based on smaller variations in the overall proportions of the animal. Carpenter used Paul's 1994 estimate of the mass of Diplodocus carnegii (11.5 tons) to speculate that A. fragillimus could have weighed up to 122.4 metric tons. The heaviest blue whale
Blue Whale
The blue whale is a marine mammal belonging to the suborder of baleen whales . At in length and or more in weight, it is the largest known animal to have ever existed....
on record weighed about 195 tons, and the heaviest dinosaur known from reasonably good remains, the Argentinosaurus
Argentinosaurus
Argentinosaurus is a genus of titanosaur sauropod dinosaur first discovered by Guillermo Heredia in Argentina. The generic name refers to the country in which it was discovered...
, weighed 80–100 tons, although if the size estimates can be validated, it would still be lighter than Bruhathkayosaurus
Bruhathkayosaurus
Bruhathkayosaurus might have been the largest dinosaur that ever lived. The accuracy of this claim, however, has been mired in controversy and debate...
, which is estimated to have weighed 139 tons.
Classification
American Naturalist
The American Naturalist is a monthly peer-reviewed scientific journal that was established in 1867. It is published by the University of Chicago Press on behalf of the American Society of Naturalists. The journal covers research in ecology, evolutionary biology, population, and integrative biology....
, and assigned them to the new genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
Amphicoelias. He placed it in a unique family, Amphicoeliidae, though this is now considered a nomen oblitum
Nomen oblitum
A nomen oblitum is a technical term, used in zoological nomenclature, for a particular kind of disused scientific name....
(forgotten name). The genus is usually assigned to the family Diplodocidae, though some modern analyses have found it at the base of the larger group Diplodocoidea
Diplodocoidea
Diplodocoidea was a superfamily of sauropod dinosaurs, which included some of the longest animals of all time, including slender giants like Supersaurus, Diplodocus, Apatosaurus, and Amphicoelias...
or as a diplodocid incertae sedis (uncertain placement). The first named species in the genus, Amphicoelias altus (holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
specimen AMHD 5764), was discovered by Cope in 1877. But while it is only represented by a partial skeleton, there are enough diagnostic characteristics to provisionally define the genus. A. altus is known from better remains, but is smaller than A. fragillimus. Cope also named a third species in 1878: Amphicoelias latus.
Osborn and Mook, in 1921, provisionally synonymized the three species, sinking A. latus into A. altus, and suggesting also that A. fragillimus is just a very large individual of A. altus, a position McIntosh agreed with in 1998. Carpenter (2006) disagreed about the synonymy of A. altus and A. fragillimus, however, citing numerous differences in the construction of the vertebra also noted by Cope, and suggested these differences are enough to warrant a separate species or even a separate genus for A. fragillimus. However, he went on to caution that the validity of A. fragillimus as a separate species is nearly impossible to determine without the original specimen to study.
In 2007, John Foster suggested that the differences usually cited to differentiate Amphicoelias altus from the more well known Diplodocus
Diplodocus
Diplodocus , or )is a genus of diplodocid sauropod dinosaur whose fossils were first discovered in 1877 by S. W. Williston. The generic name, coined by Othniel Charles Marsh in 1878, is a Neo-Latin term derived from Greek "double" and "beam", in reference to its double-beamed chevron bones...
are not significant and may be due to individual variation. Foster argued that Amphicoelias is probably the senior synonym of Diplodocus, and that if further research bears this out, the familiar name Diplodocus would need to be abandoned in favor of Amphicoelias, as was the case with Brontosaurus and its senior synonym Apatosaurus
Apatosaurus
Apatosaurus , also known by the popular but scientifically deprecated synonym Brontosaurus, is a genus of sauropod dinosaur that lived from about 154 to 150 million years ago, during the Jurassic Period . It was one of the largest land animals that ever existed, with an average length of and a...
.
Paleobiology
In his 2006 re-evaluation, Carpenter examined the paleobiology of giant sauropods, including Amphicoelias, and addresses the question of why this group attained such a huge size. He pointed out that gigantic sizes were reached early in sauropod evolution, with very large sized species present as early as the late TriassicTriassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
Period, and concluded that whatever evolutionary pressure caused large size was present from the early origins of the group. Carpenter cited several studies of giant mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
ian herbivores, such as elephant
Elephant
Elephants are large land mammals in two extant genera of the family Elephantidae: Elephas and Loxodonta, with the third genus Mammuthus extinct...
s and rhinoceros
Rhinoceros
Rhinoceros , also known as rhino, is a group of five extant species of odd-toed ungulates in the family Rhinocerotidae. Two of these species are native to Africa and three to southern Asia....
, which showed that larger size in plant-eating animals leads to greater efficiency in digesting food. Since larger animals have longer digestive systems, food is kept in digestion for significantly longer periods of time, allowing large animals to survive on lower-quality food sources. This is especially true of animals with a large number of 'fermentation chambers' along the intestine which allow microbes to accumulate and ferment plant material, aiding digestion. Throughout their evolutionary history, sauropod dinosaurs were found primarily in semi-arid, seasonally dry environments, with a corresponding seasonal drop in the quality of food during the dry season. The environment of Amphicoelias was essentially a savanna
Savanna
A savanna, or savannah, is a grassland ecosystem characterized by the trees being sufficiently small or widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach the ground to support an unbroken herbaceous layer consisting primarily of C4 grasses.Some...
, similar to the arid environments in which modern giant herbivores are found, supporting the idea that poor-quality food in an arid environment promotes the evolution of giant herbivores. Carpenter argued that other benefits of large size, such as relative immunity from predators, lower energy expenditure, and longer life span, are probably secondary advantages.
The Morrison Formation
Morrison Formation
The Morrison Formation is a distinctive sequence of Late Jurassic sedimentary rock that is found in the western United States, which has been the most fertile source of dinosaur fossils in North America. It is composed of mudstone, sandstone, siltstone and limestone and is light grey, greenish...
environment in which Amphicoelias lived would have resembled a modern savanna, though since grass
Grass
Grasses, or more technically graminoids, are monocotyledonous, usually herbaceous plants with narrow leaves growing from the base. They include the "true grasses", of the Poaceae family, as well as the sedges and the rushes . The true grasses include cereals, bamboo and the grasses of lawns ...
did not appear until the Late Cretaceous
Late Cretaceous
The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...
, fern
Fern
A fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...
s were probably the dominant plant and main food source for Amphicoelias. Though Engelmann et al. (2004) dismissed ferns as a sauropod food source due to their relatively low caloric content, Carpenter argued that the sauropod digestive system, well adapted to handle low-quality food, allows for the consumption of ferns as a large part of the sauropod diet. Carpenter also noted that the occasional presence of large petrified logs indicate the presence of 20–30 m (65–100 ft) tall trees, which would seem to conflict with the savanna comparison. However, the trees are rare, and since tall trees require more water than the savanna environment could generally provide, they probably existed in narrow tracts or 'gallery forests' along rivers and gulleys where water could accumulate. Carpenter speculated that giant herbivores like Amphicoelias may have used the shade of the gallery forests to stay cool during the day, and done most of their feeding on the open savanna at night.
External links
- Discussion on the Dinosaur Mailing List:
- Amphicoelias - DinoData entry