The cervical vertebrae were less elongated and more heavily constructed than those of Diplodocus and the bones of the leg were much stockier (despite being longer), implying a more robust animal. The tail was held above the ground during normal locomotion. Like most sauropods, Apatosaurus had only a single large claw on each forelimb, with the first three toes on the hind limb possessing claws.
Apatosaurus was a large, long-necked quadrupedal animal with a long whip-like tail. Its forelimbs were slightly shorter than its hindlimbs. One measurement places the total length of Apatosaurus at 26 meters (85 ft) and its weight at 24-32 tons, roughly the weight of four elephants.
The skull was small in proportion to the size of the animal. The jaws were lined with spatulate teeth, which resembled chisels, suited to a herbivorous diet.
Apatosaurus is a member of the family Diplodocidae, a clade of gigantic sauropod dinosaurs. The family includes some of the longest creatures ever to walk the earth, including Diplodocus, Supersaurus, Suuwassea, and Barosaurus. Within the subfamily Apatosaurinae, Apatosaurus may be most closely related to Suuwassea, Supersaurus and Eobrontosaurus.
In 1877, Othniel Charles Marsh published the name of the holotype species Apatosaurus ajax, which he called after the hero Ajax from Greek mythology. Since then, two partial skeletons of A. ajax have been found, including part of a skull. He followed this in 1879 with a description of another, more complete specimen, which he thought represented a new genus and named Brontosaurus excelsus. In 1903, Elmer Riggs decided that Brontosaurus excelsus was so similar to Apatosaurus ajax that it belonged in the same genus. Riggs then re-classified the species as Apatosaurus excelsus. According to the rules of the ICZN (which governs the scientific names of animals), the name Apatosaurus, having been published first, had priority as the official name; Brontosaurus was a junior synonym and therefore discarded from formal use.
Apatosaurus excelsus is known from six partial skeletons, including part of a skull, which have been found in the United States, in Colorado, Oklahoma, Utah, and Wyoming. Apatosaurus louisae was named by William Holland in 1915 in honor of Mrs. Louise Carnegie, wife of Andrew Carnegie who funded field research to find complete dinosaur skeletons in the American West. Apatosaurus louisae is known from one partial skeleton which was found in Colorado in the United States. Apatosaurus parvus was originally known as Elosaurus parvus, but was reclassified as a species of Apatosaurus in 1994. This synonymy was upheld in 2004.
Apatosaurus yahnahpin was named by Filla and Redman in 1994. Robert T. Bakker made A. yahnahpin the type species of a new genus, Eobrontosaurus in 1998, so it is now properly Eobrontosaurus yahnahpin.
Othniel Charles Marsh, a Professor of Paleontology at Yale University, described and named an incomplete juvenile skeleton of Apatosaurus ajax in 1877. Two years later, Marsh announced the discovery of a larger and more complete specimen at Como Bluff, Wyoming — which, because of discrepancies including the size difference, Marsh misidentified as belonging to an entirely new genus and species. He dubbed the new species Brontosaurus excelsus, meaning "thunder lizard", from the ancient Greek brontē/βροντη meaning 'thunder' and sauros/σαυρος meaning 'lizard', and from the Latin excelsus, "to exceed in number", referring to the greater number of sacral vertebrae than in any other genus of sauropod known at the time.
The finds, representing the largest dinosaur discovered at the time, were nearly complete, lacking only a head, feet, and portions of the tail. They were then prepared for what was to be the first ever mounted display of a sauropod skeleton, at Yale's Peabody Museum of Natural History in 1905. The missing bones were created using pieces from known close relatives of Brontosaurus. Sauropod feet that were discovered at the same quarry were added, as well as a tail fashioned to appear as Marsh believed it should, and a composite model of what he felt the skull of this massive creature might look like. This was not a delicate Diplodocus-style skull, which would later turn out to be more accurate,), but was composed of "the biggest, thickest, strongest skull bones, lower jaws and tooth crowns from three different quarries", consisting primarily of those of Camarasaurus, the only other sauropod for which good skull material was known at the time. This method of reconstructing incomplete skeletons based on the more complete remains of related dinosaurs continues in museum mounts and life restorations to-date.
Despite the much-publicized debut of the mounted skeleton, which cemented the name Brontosaurus in the public consciousness, Elmer Riggs had published a paper in the 1903 edition of Geological Series of the Field Columbian Museum which argued that Brontosaurus was not different enough from Apatosaurus to warrant its own genus, and created the combination Apatosaurus excelsus: "In view of these facts the two genera may be regarded as synonymous. As the term 'Apatosaurus' has priority, 'Brontosaurus' will be regarded as a synonym."
Despite this, at least one paleontologist—Robert Bakker—argued in the 1990s that A. ajax and A. excelsus are in fact sufficiently distinct that the latter continues to merit a separate genus. In 2015 Emanuel Tschopp, Octávio Mateus, and Roger Benson released a paper that argued that Apatosaurus excelsus, originally classified as Brontosaurus excelsus, had enough morphological differences from other species of Apatosaurus that it warranted being reclassified as a separate genus again. The conclusion was based on a comparison of 477 morphological characteristics across 81 different dinosaurs. Among the many notable differences were the wider - and presumably stronger - neck of other Apatosaurus species compared to A. excelsus. Other species previously assigned to Apatosaurus, such as Elosaurus parvus and Eobrontosaurus yahnahpin were also reclassified as Brontosaurus. However, some are skeptical of the large number of sauropod taxa in the Morrison, instead grouping taxa like Brontosaurus and Apatosaurus together.
Early on, it was believed that Apatosaurus was too massive to support its own weight on dry land, so it was theorized that the sauropod must have lived partly submerged in water, perhaps in a swamp, but recent findings do not support this. In fact, like its relative Diplodocus, Apatosaurus was a grazing animal with a very long neck and a long tail that served as a counterweight. One study found that diplodocid necks were less flexible than previously believed, and that sauropods like Apatosaurus were adapted to low browsing or ground feeding.
In 2008, footprints of juvenile Apatosaurus were reported from Quarry Five in Morrison, Colorado. Discovered in 2006 by Matthew Mossbrucker, these footprints show that juveniles could run on their hind legs in a manner similar to that of the modern basilisk lizard.
In the early 20th century, diplodocids like Apatosaurus were often portrayed with their necks held high up in the air, allowing them to graze from tall trees. More recently, scientists have argued that the heart would have had trouble sustaining sufficient blood pressure to oxygenate the brain. Furthermore, more recent studies have shown that the structure of the neck vertebrae would not have permitted the neck to bend far upwards. However, subsequent studies demonstrated that all tetrapods appear to hold their necks at the maximum possible vertical extension when in a normal, alert posture, and argued that the same would hold true for sauropods barring any unknown, unique characteristics that set the soft tissue anatomy of their necks apart from other animals. Apatosaurus like Diplodocus would have held its neck at about a 45 degree angle with the head pointed downwards in a resting posture.
With Apatosaurus possessing such a large body mass, combined with a long neck, physiologists have had problems determining how the animals managed to breathe.
Beginning with the assumption that Apatosaurus, like crocodilians, did not have a diaphragm, the dead-space volume (the amount of unused air remaining in the mouth, trachea and air tubes after each breath) has been estimated at about 184 liters for a 30 ton specimen.
- 904 liters if avian
- 225 liters if mammalian
- 19 liters if reptilian.
On this basis, its respiratory system could not have been reptilian, as its tidal volume would not have been able to replace its dead-space volume. Likewise, the mammalian system would only provide a fraction of new air on each breath. Therefore, it must have had either a system unknown to modern science or an avian system, i.e. multiple air sacs and a flow-through lung. Furthermore, an avian system would only need a lung volume of about 600 liters compared to a mammalian requirement of 2,950 liters, which would exceed the available space. The overall thoracic volume of Apatosaurus has been estimated at 1,700 liters allowing for a 500-liter, four-chambered heart (like birds, not three-chambered like reptiles) and a 900-liter lung capacity. That would allow about 300 liters for the necessary tissue. Assuming Apatosaurus had an avian respiratory system and a reptilian resting-metabolism, it would need to consume only about 262 liters (69 gallons) of water per day.
An article that appeared in the November 1997 issue of Discover Magazine reported research into the mechanics of Apatosaurus tails by Nathan Myhrvold, a computer scientist from Microsoft. Myhrvold carried out a computer simulation of the tail, which in diplodocids like Apatosaurus was a very long, tapering structure resembling a bullwhip. This computer modeling suggested that sauropods were capable of producing a whip-like cracking sound of over 200 decibels, comparable to the volume of a cannon.
Apatosaurus is one of the most recognizable dinosaurs. It has appeared a lot of times in pop culture.Brontosaurus has often been depicted in cinema, beginning with Winsor McKay's 1914 classic Gertie the Dinosaur. The 1925 silent film The Lost World featured, using special effects by Willis O'Brien, a battle between a Brontosaurus and an Allosaurus but the former inaccurately had a very bendy neck. When George Lucas made his special edition of Star Wars Episode IV: A New Hope in 1997, he added some large, long-necked animals based on the Brachiosaurus digital model from the earlier film Jurassic Park. At an early stage he altered the CG department's suggested name "Bronto", taken from Brontosaurus, to 'Ronto'. In the movie The Land Before Time and the sequels a Apatosaurus named Littlefoot was one of the main characters. Sinclair Oil has a long history of being a fixture on American roads (and briefly in other countries) with its green dinosaur logo and mascot, an Apatosaurus (Brontosaurus). While Sinclair's early advertising included a number of different dinosaurs, eventually only Apatosaurus was used as the official logo, due to its popular appeal.
The Brontosaurus is the main plot focus of the 1985 movie Baby: Secret of the Lost Legend, in which a family of Brontosaurs are found still living in Africa.
Apatosaurus was in the third segment, the Jurassic segment of the famous documentary When Dinosaurs Roamed America, where a herd of them were hunted by a pack of Allosaurus .
- Skeletal drawings of diplodocids including Apatosaurus ajax, B. excelsus, and A. louisae from SkeletalDrawing.com
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