Apatosaurus also formerly known as Brontosaurus, is a genus of sauropod dinosaur that lived about 150 million years ago, during the Jurassic Period (Kimmeridgian and Tithonian ages). It was one of the largest land animals that ever existed, with an average length of 23 meters (75 ft) and a mass of at least 23 metric tons (25 short tons). The name Apatosaurus means 'deceptive lizard', so-given because the chevron bones were similar to those of a prehistoric marine lizard, Mosasaurus. The name Apatosaurus comes from the Greek ἀπατέλος or ἀπατέλιος meaning 'deceptive' and σαῦρος meaning 'lizard'.
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 tremendously large long-necked quadrupedal animal with a long whip-like tail. Its forelimbs were slightly longer 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 comparison with the size of the animal. The jaws were lined with spatulate teeth, which resembled chisels, suited to a herbivorous diet.
In 1877, Othniel Charles Marsh published the name of the type species Apatosaurus ajax. 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 pointed out that Brontosaurus excelsus was in fact so similar to Apatosaurus ajax that it belonged in the same genus, and which Riggs re-classified 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 ajax is the type species of the genus, and was named by the paleontologist Othniel Charles Marsh in 1877 after Ajax, the hero from Greek mythology. It is the holotype for the genus and two partial skeletons have been found, including part of a skull. Apatosaurus excelsus (originally Brontosaurus) was named by Marsh in 1879. It 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.
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Cladogram of the Diplodocidae after Lovelace, Hartman, and Wahl, 2008.
Robert T. Bakker made A. yahnahpin the type species of a new genus, Eobrontosaurus in 1998, so it is now properly Eobrontosaurus yahnahpin. It was named by Filla, James and Redman in 1994. One partial skeleton has been found in Wyoming. However, recently it has been argued that Eobrontosaurus belongs within Camarasaurus.
Apatosaurus is a member of the 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 and Supersaurus.
Othniel Charles Marsh, a Professor of Paleontology at Yale University, described and named an incomplete (and 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 incorrectly identified as belonging to an entirely new genus and species. He dubbed the new species Brontosaurus excelsus, meaning "thunder lizard", from the 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 — the largest dinosaur ever discovered at the time and nearly complete, lacking only a head, feet, and portions of the tail — 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 known pieces from 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, as well as 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", primarily 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 this day.
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:
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. This idea has not been accepted by many palaeontologists.
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.
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.
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 in the modern world or one like birds, 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.
It is not known how Apatosaurs ate enough food to satisfy their enormous bodies. It is likely that they ate constantly, pausing only to cool off, drink or to remove parasites. It is surmised that they slept standing upright. They likely relied on their enormous size and herd behavior to deter predators.
The length of time taken for Marsh's misclassification to be brought to public notice meant that the name Brontosaurus, associated as it was with one of the largest dinosaurs, became so famous that it persisted long after the name had officially been abandoned in scientific use. The terms brontosaurus, brontosaurs, and brontosaurians (no capital 'B'; no italics) are often used to refer generically to any of the sauropod dinosaurs.
As late as 1989, the U.S. Post Office issued four "dinosaur" stamps, Tyrannosaurus, Stegosaurus, "Pteradon" (misspelling of Pteranodon, which is a pterosaur and not a dinosaur) and Brontosaurus. The inclusion of these last two led to complaints of "fostering scientific illiteracy." The Post Office defended itself (in Postal Bulletin 21744) thus:
Stephen Jay Gould supported this position in his essay "Bully for Brontosaurus", though he echoed Riggs' original argument that "Brontosaurus" is a synonym for "Apatosaurus". Nevertheless, he noted that the creature has developed and continues to maintain an independent existence in the popular imagination.
Since the beginning of film history, Brontosaurus has been depicted in cinema. For example, the 1925 silent film The Lost World featured, using special effects by Willis O'Brien, a battle between a Brontosaurus and an Allosaurus. King Kong (1933) featured a Brontosaurus, as did the 2005 remake, described using the fictional scientific name "Brontosaurus baxteri", or Baxter's Thunder-Lizard, after a character in the film. The brontosaur of the 2005 film is noticeably different from the modern view of Apatosaurus, with a square head, low-hanging tail, and snake-like neck reminiscent of 1930s period depictions of the species in art.