Apatosaurus/Brontosaurus

[Barry the Baryonyx]

Apatosaurus/Brontosaurus

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Genus of giant herbivorous dinosaur, one of the largest land animals of all time. Apatosaurus lived between 147 million and 137 million years ago during the Late Jurassic and Early Cretaceous Periods in North America and Europe. It weighed as much as 30 tons and was as long as 70 ft (21 m), including the very long neck and tail. Formerly known as Brontosaurus because of incomplete fossil evidence, its head was depicted until 1978 as massive and snub-nosed, with sthangylike teeth; scientists now know the animal had a slender, elongated skull and long, peglike teeth. Skeletal evidence indicates that, despite their great bulk, apatosaurs were primarily land animals.

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Apatosaurus, [Gr.,=deceptive lizard], quadruped saurischian dinosaur, estimated to be from 70 to 90 ft (21 to 27 m) in length and to weigh up to 30 tons (27 metric tons). Apatosaurus was called Brontosaurus [Gr.,=thunder lizard] until it was discovered that the two animals were, in fact, the same. Paleontologist O. C. Marsh named a specimen he uncovered in 1877 Apatosaurus ajax. Marsh discovered parts of a second fossil skeleton in 1879 and, not recognizing it as the same animal, called it Brontosaurus excelsius. Since the name Apatosaurus was published first, it takes priority as the valid name, although Brontosaurus continues to be used popularly. It is one of the best known dinosaurs. Apatosaurus had a long, whiplike tail, stout legs, and a long neck. It was herbivorous and dwelled on land, possibly in forests, using its long neck to feed from trees. The eyes and nostrils were located toward the top of the skull. It flourished in the late Jurassic period. Apatosaurus bones and those of other sauropods have long been excavated in the Morrison formation of the late Jurassic and early Cretaceous strata in Colorado, Wyoming, and other Western states. No satisfactory skull specimen has been discovered attached to an Apatosaurus, and for many years an incorrect Camarasaurus-like head was mounted on the famous skeleton on display at the American Museum of Natural History in New York City. Apatosaurus is related to Diplodicus and Barosaurus.

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Apatosaurus, previously known as Brontosaurus, is a genus of sauropod dinosaurs that lived about 140 million years ago, during the Jurassic Period. They were some of the largest land animals that ever existed, about 4.5 metres (15 feet) tall at the hips, with a length of up to 21m (70 feet) and a mass up to 35 metric tonnes (40 tons). Their name means 'deceptive lizard', so-named because the chevron bones were like those of Mosasaurus (Greek apatelos or apatelios meaning 'deceptive' and sauros meaning 'lizard'). The cervical vertebrae and the bones in the legs were bigger and heavier than that of Diplodocus although, like Diplodocus, Apatosaurus also had both a long neck and a long tail. The tail was held above the ground during normal locomotion. Like most sauropods, Apatosaurus had only a single large claw on each forelimb. The skull was first identified in 1975, a century after this dinosaur acquired its name.


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 Oklahoma, Utah, and Wyoming. A. louisae was named by William Holland, in 1915. It 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. On March 23 1983 the Apatosaurus was made the official state dinosaur of Guam.


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 30kg 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 certainly could not fly), 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.


Classification


Apatosaurus is a member of the Diplodocidae, along with Diplodocus, Barosaurus and Seismosaurus, although it is not as closely related to the others as they are to each other and hence placed in its own subfamily Apatosaurinae.


Apatosaurus/Brontosaurus controversy


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.

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