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'''Apatosaurus''' (), popularly (though incorrectly) known as ''Brontosaurus'', is a genus of sauropod dinosaur that lived about 140 million years ago, during the Jurassic Period. 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 like those of ''Mosasaurus'' (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 hindlimb possessing claws.

Contents

Discovery and species

''Apatosaurus''/''Brontosaurus''

Paleobiology

Neck

Physiology

Tail

Classification

See also

References

Discovery and species

Fossils of this animal have been found in Nine Mile Quarry and Bone Cabin Quarry in Wyoming and at sites in Colorado, Oklahoma and Utah, USA.

★ ''A. 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.

★ ''A. 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.

★ ''A. 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. A. louisae is known from one partial skeleton which was found in Colorado in the United States.
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.

''Apatosaurus''/''Brontosaurus''

In 1877, Othniel Charles Marsh published notes on his discovery of ''Apatosaurus ajax''. He followed this in 1879 with a description of another, more complete, dinosaur specimen. He speculated that the latter specimen represented a new genus and named it ''Brontosaurus excelsus''. In 1903, it was discovered that ''Brontosaurus excelsus'' was in fact an adult ''Apatosaurus'' and the name ''Apatosaurus'', having been published first, was deemed to have priority as the official name; ''Brontosaurus'' was relegated to being a synonym. In the 1970s, it was proven that the traditional "Brontosaurus" image known to all was, in fact, an ''Apatosaurus excelsus'' with a ''Camarasaurus'' head incorrectly placed on its body.^[1]

Paleobiology

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. 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. Fossilized footprints indicate that it probably lived in herds. To aid in processing food, ''Apatosaurus'' may have swallowed gizzard stones (gastroliths) in the same way that many birds do today, as its jaws lacked molars with which to chew tough plant fibers.

Neck

''Apatosaurus'' browsed the tops of trees, on riverbanks. Scientists believe that these sauropods could not raise their necks to an angle of 90 degrees, as doing so would slow blood flow to the brain excessively; blood starting at the body proper would take two or more minutes to reach the brain. Furthermore, studies of the structure of the neck vertebrae have revealed that the neck was not as flexible as previously thought.

Physiology

With such a large body mass, combined with a long neck, physiologists encounter problems determining how these 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.
Its tidal volume (the amount of air moved in or out during a single breath) has been calculated based on the following respiratory systems:

★ 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 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.

Tail

An interesting speculation was reported by the ''Discover Magazine'' in 1997 about "whipcracking" millions of years ago. Nathan Myhrvold, a computer scientist from Microsoft, carried out a computer simulation of the tail of Apatosaurus, a very long, tapering tail resembling a whip, and concluded that sauropods were capable of producing a crack of over 200 decibels, comparable to the sound of a cannon.^[2]

Classification

''Apatosaurus'' is a member of the 'Diplodocidae', along with ''Diplodocus'' and ''Barosaurus'', although it is not as closely related to these genera as they are to each other, and hence ''Apatosaurus'' is usually placed in its own subfamily, Apatosaurinae, along with its close relative ''Supersaurus''.^[3][4]

See also

★ Brontosaurus

References

1. McIntosh JS. & Berman DS. (1975): Description of the palate and lower jaw of the sauropod dinosaur ''Diplodocus'' (Reptilia: Saurischia) with remarks on the nature of the skull of ''Apatosaurus''. ''Journal of Paleontology'' 49(1): 187-199
2. "Dinosaur in Motion", ''Discover'' November 1997
3. Taylor, M.P. & Naish, D. 2005. The phylogenetic taxonomy of Diplodocoidea (Dinosauria: Sauropoda). ''PaleoBios'' 25(2): 1-7. (download here)
4. Harris, J.D. 2006. The significance of ''Suuwassea emiliae'' (Dinosauria: Sauropoda) for flagellicaudatan intrarelationships and evolution. ''Journal of Systematic Palaeontology'' 4(2): 185–198.


★ The Complete Dinosaur, Frank V. Paladino, James R. Spotila, Peter Dodson, , , Indiana University Press, , 0253333490