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Amphicoelias
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Sauropsida
clade: Dinosauria
Superorder: Sauropodomorpha
Family: Diplodocidae
Genus: Amphicoelias
Cope, 1878
Type species
Amphicoelias altus
Cope, 1878a

Amphicoelias (/ˌæmfᵻˈsiːliəs/, meaning "biconcave", from the Greek αμφι, amphi: "on both sides", and κοιλος, koilos: "hollow, concave") is a genus of herbivorous sauropod dinosaur.

However, A 2021 study found A. altus is not dubious, and thus, the genus is preserved.[1][2]

Description[]

The type species of Amphicoelias, A. altus, was named by paleontologist Edward Drinker Cope 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. fragillimus, in the same paper. However, all subsequent researchers have considered A. fragillimus to be a synonym of A. altus. Even by 1881 however, it was recognized that A. altus could not be distinguished from other genera, as the features described by Cope were misinterpreted and are widespread. 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 dentition of Amphicoelias is homodont. Its teeth are shaped like long slender cylindrical rods, are spaced apart and project forward towards the front of the mouth. 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 meters (82 feet) long. While most scientists have used these details to distinguish Amphicoelias and Diplodocus as separate genera, at least one has suggested that Amphicoelias is probably the senior synonym of Diplodocus.

History[]

In 1884 Cope's description of A. fragillimus has been met with skepticism, with some researchers noting that there were typographical errors in his measurements. For example, the measurement units are given in (obviously incorrect) centimeters rather than millimeters. Carpenter argued that there is every reason to take Cope at his word, noting tha

t 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.

In 2015, Woodruff and Foster published an analysis of the evidence and circumstances surrounding the publication and interpretation of A. fragillimus. A recent, 2021 study found A. altus is not likely dubious, and thus, the genus is preserved.[3]

A 2021 analysis reassured that Amphicoelias was distinct, noting a much higher sauropod diversity in the Morrison than historically expected.[4]

tion and species[]

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).[13] 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 second species in 1878: Amphicoelias latus.

The third named Amphicoelias species, A. fragillimus, was 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. Based only on an illustration published in 1878, this vertebra would have measured 2.7 metres (8.9 ft) tall in life. However, it has been argued that the scale bar in the published description contained a typographical error, and the fossil vertebra was in fact only 1.38 metres (4.5 ft) tall. In addition to this 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. 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".

Osborn and Mook, in 1921, provisionally synonymized the three species, sinking A. latus into Camarasaurus supremus, and suggesting also that A. fragillimus is just a very large individual of A. altus, a position which most subsequent studies, including McIntosh 1998, Foster (2007), and Woodruff and Foster (2015) have agreed with. 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. Although Amphicoelias latus is clearly not Amphicoelias, it is probably synonymous with Camarasaurus grandis rather than C. supremus because it was found lower in the Morrison Formation and the deeply concave articular faces on the caudal vertebrae are more consistent with C. grandis.

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. In 2015, Woodruff and Foster reiterated this conclusion, stating that there is only one species of Amphicoelias and that it could be referred to Diplodocus as Diplodocus altus. They considered the name Amphicoelias to be a nomen oblitum. It has also been hypothesized that Amphicoelias should be considered an apatosaurine, and therefore should be placed in the subfamily Apatosaurinae.

The following cladogram of the Diplodocidae after Tschopp, Mateus, and Benson (2015) instead shows A. altus outside Diplodocinae.

Diplodocidae 	

Amphicoelias altus


Apatosaurinae 	

Unnamed species



Apatosaurus ajax


Apatosaurus louisae



Brontosaurus excelsus


Brontosaurus yahnahpin


Brontosaurus parvus



Diplodocinae 	

Unnamed species


Tornieria africana



Supersaurus lourinhanensis


Supersaurus vivianae



Leinkupal laticauda


Galeamopus hayi



Diplodocus carnegii


Diplodocus hallorum



Kaatedocus siberi


Barosaurus lentus

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 Triassic 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 mammalian herbivores, such as elephants 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, ferns 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 (66–98 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.

Media[]

A sauropod that can potentially be pinpointed as an Amphicoelias fragillimus appears in The Land Before Time TV series episode, "The Hidden Canyon". The identification comes from the fact that, while the size of a normal Land Before Time adult "Longneck", it uses a model usually only used for young characters, such as Littlefoot and Ali. This could potentially mean that the individual represents a juvenile of an even larger dinosaur; likely the behemoth A. fragillimus described by Cope in 1870.

References[]

SauropodSize

Maraapunisaurus (which was once thought to be an amphicoelias) was the biggest and longest dinosaur

Dinosaurios-a-amphicoelias 0002

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Gallery[]

Amphicoelias/Gallery

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