Maraapunisaurus is a genus of sauropod dinosaur from the Late Jurassic Morrison Formation of western North America. It contains one species, Maraapunisaurus fragillimus, which was originally named Amphicoelias fragillimus. It has sometimes been estimated to be the largest dinosaur specimen ever discovered. Based on surviving descriptions of a single fossil bone, scientists have produced numerous size estimates over the years; the largest estimate M. fragillimus to have been the longest known animal at in length with a mass of . However, because the only fossil remains were lost at some point after being studied and described in the 1870s, evidence survived only in contemporary drawings and field notes.
More recent studies have made a number of suggestions regarding the possibility of such an animal. One analysis of the surviving evidence, and the biological plausibility of such a large land animal, has suggested that the enormous size of this animal were over-estimates due partly to typographical errors in the original 1878 description. More recently, it was suggested by paleontologist Kenneth Carpenter that the species is a rebbachisaurid, rather than a diplodocid sauropod. He therefore used Limaysaurus instead of Diplodocus as a basis for size estimates. This resulted in a smaller, animal, and he dismissed the idea that there must have been typographical errors. Since then, somewhat larger size estimates have been made, placing Maraapunisaurus at 70 ―120 tons in mass and long, which still makes Maraapunisaurus the third-longest known vertebrate to have ever lived, behind Bruhathkayosaurus and Supersaurus specimen BYU 9024. Maraapunisaurus also has the tallest and largest neural spine out of any animal ().
History of study Original description
The holotype and only known specimen of Maraapunisaurus fragillimus was collected by Oramel William Lucas, shortly after he had been hired as a fossil collector by the renowned paleontologist Edward Drinker Cope, in 1877. Lucas discovered a partial vertebra (the neural arch including the spine) of a new sauropod species in Garden Park, north of Cañon City, Colorado, close to the quarry that yielded the first specimens of Camarasaurus. The vertebra was in poor condition, but astonishingly large. It was probably colored a very pale tan, tinted with maroon, like most fossils from the same area. The preserved parts perhaps measured in height; its original height might have been as tall as .Carpenter, K. (2006). "Biggest of the big: a critical re-evaluation of the mega-sauropod Amphicoelias fragillimus." In Foster, J.R. and Lucas, S.G., eds., 2006, Paleontology and Geology of the Upper Jurassic Morrison Formation. New Mexico Museum of Natural History and Science Bulletin 36: 131–138. Lucas sent the specimen to Cope's house in Philadelphia in the spring or early summer of 1878, and Cope published it as the holotype specimen of a new species in the genus Amphicoelias as A. fragillimus, that August. In addition to this vertebra, Cope's 1879 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. This specimen was never formally referred to the species. Maraapunisaurus means 'huge reptile' based on maraapuni, the Southern Ute for 'huge'.
The specific name was chosen to express that the fossil was "very fragile", referring to the delicateness of the bone produced by very thin laminae (vertebral ridges). In 1902, Oliver Perry Hay hypercorrected the name to the Latin fragilissimus,Hay, Oliver Perry, 1902, Bibliography and Catalogue of the Fossil Vertebrata of North America, Governmental Printing Office, 868 pp but such emendations are not allowed by the ICZN (International Code of Zoological Nomenclature). In any case, fragillimus is the correct superlative of fragilis in Latin. 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", also sometimes known simply as "the Nipple" or "Saurian Hill".
Disappearance of the specimen and quarry
The gigantic vertebra has often been ignored in summaries of the largest dinosaurs partly because, according to subsequent reports, the whereabouts of both the vertebra and the femur are unknown, and all attempts to locate them have failed. Kenneth Carpenter, in 2006, presented a possible scenario for the disappearance of the specimen. 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 Othniel Charles Marsh, was the first to use such resins, in the early 1880s). Carpenter observed that the fossil bones known from the 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 2018, Carpenter recounted how Cope's collections were after his death sold to the American Museum of Natural History in 1897. While cataloging them, William Diller Matthew was unable to locate many important pieces, among them the holotype of A. fragillimus. Because of the possibility that it would turn up eventually, it was given the catalog number AMNH 5777.
In 1994, an attempt was made to relocate the original quarry where the species and others had been found, using ground-penetrating radar to image bones still buried in the ground. The attempt failed because the fossilized mudstone bones were the same density as the surrounding rock, making it impossible to differentiate between the two. A study of the local topography also showed that the fossil-bearing rock strata were severely eroded, and probably were so when Lucas discovered M. fragillimus, suggesting that a majority of the skeleton had already disappeared when the vertebra was recovered.
Modern interpretations
The giant proportions of the vertebra have been debated by paleontologists. Carpenter has 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 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. Other paleontologists have been more critical. In a 2015 analysis of the evidence and circumstances surrounding the publication and interpretation of the discovery, Cary Woodruff and John R. Foster concluded that the vertebra's size has been over-estimated and that modern paleontologists were accepting Cope's interpretation without due skepticism. They note that no comparably gigantic sauropod fossils have been discovered in the Morrison Formation or elsewhere, that 19th century paleontologists – including Cope himself – paid no attention to the size of fossil (even when it may have substantiated Cope's rule of size increase in animal lineages over time), and that typographical errors in his measurements – such as reporting vertebral measurements in meters rather than millimeters – undermine their reliability. It was suggested that the real height of the preserved specimen was just . They concluded that the super-gigantic M. fragillimus is a "highly unlikely" creature based on unquestioning interpretation of Cope's report.
In 2018, Carpenter once again defended the original measurements given by Cope in a paper re-describing the species based on Cope's illustration and description. The argument of a typographical error pointed to Cope's use of the abbreviation "m" rather than "mm" for millimeters, the same as used for meters, but Carpenter points out a capital "M" is used for meters, and that this was a standard method of abbreviation in the time period. In addition to this, he pointed to the communication between Lucas and Ferdinand Vandeveer Hayden, a survey geologist, where the large size was repeated without question. Lucas also often made his own specific measurements and annotated drawings of his fossils, so Carpenter considers it unlikely he would have been merely re-stating what Cope had said. Later, in 1880, Lucas included specific mention of the specimen in his autobiography, noting "[w]hat a monster the animal must have been," refuting the idea that no attention was given to the importance of the vertebra. Carpenter was critical of the typographical theory, saying: "It is unfortunate that they seek to disprove Cope’s claim by casting aspersions about the quality of his work and go so far as to alter Cope’s measurements."
Upon studying the drawing of the specimen again, Carpenter found that it bore a strong resemblance to the vertebrae of rebbachisaurid diplodocoids; previously it had been allied with the type species of Amphicoelias, A. altus, as a diplodocid or primitive diplodocoid. Considering it to be a rebbachisaurid upon his re-examination, the species could not be referred to the genus Amphicoelias, and so he gave it a new generic name, Maraapunisaurus. Apparently, Carpenter was inspired by work of paleontology enthusiasts posted on the website DeviantArt; one user, Zachary Armstrong, known as "palaeozoologist" on the website, conjectured the same classification in 2014, four years before Carpenter's publication. He is credited in the acknowledgements of the paper. Naming a genus based on a lost specimen is rare, but he pointed out that the ICZN explicitly allows it, and the genus Nopcsaspondylus had been named in a similar fashion. The generic name is derived from the Southern Ute word "Ma-ra-pu-ni", meaning "huge", and the Latinised Greek saurus, meaning reptile. The name was suggested to Carpenter by the Southern Ute Cultural Department, based in Ignacio, Colorado.
Description Size
Any size estimate of M. fragillimus must be regarded with caution because of the lack of specimens and detailed, accurate documentation of its fossils. All size estimates are based on Cope's original description, which has somewhat vague measurements. It has also been suggested that it contains potentially critical typographical errors, but this idea has been disputed.
Producing an estimate of the complete size of M. fragillimus requires scaling the bones of better-described, closely related species based on the assumption that their relative proportions were similar. In his original paper, Cope did this while speculating on the size of a hypothetical M. fragillimus femur (upper leg bone). Cope stated that in other sauropod dinosaurs, specifically Amphicoelias altus and Camarasaurus supremus, the femora were always twice as tall as the tallest dorsal (back) vertebra, and estimated the size of an M. fragillimus femur to be tall.