Apatosaurus
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{{Taxobox
| color = pink
| name = Apatosaurus
| status = Conservation status: Fossil
| image = Apatosaurus.gif
| image_width=240px
| regnum = Animalia
| phylum = Chordata
| classis = Sauropsida
| superordo = Dinosauria
| ordo = Saurischia
| subordo = Sauropodomorpha
| infraordo = Sauropoda
| familia = Diplodocidae
| genus = Apatosaurus
| genus_authority = Marsh, 1877
| subdivision_ranks = Species
| subdivision =
Apatosaurus ajax
Apatosaurus excelsus
Apatosaurus louisae
}}
Apatosaurus (pronounced Template:IPA) meaning "deceptive lizard", because its chevron bones were like those of Mosasaurus (Greek apatelos = deceptive + sauros = lizard), often referred to 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 25m (80 feet) and a mass up to 35 metric tonnes (40 tons).
The cervical vertebra and the bones in the legs were bigger and heavier than that of Diplodocus, but they both had the long neck and tail. The skull was first identified in 1975, a century after it got its name. Apatosaurus had a large claw on its first digit (thumb). The tail was held above the ground during normal locomotion.
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Environment
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) the same way many birds do today — its jaws alone were not sufficient to chew tough plant fibers.
Apatosaurus lumbered along in flocks on riverbanks with trees, eating off the top leaves. 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. No one knows how Apatosaurs ate enough food to satisfy their enormous bodies. They probably ate constantly, pausing only to cool off, drink or to remove parasites. They must have slept standing upright. If attacked by a predator, one could defend itself by swinging its tail from side to side, or stomping on the meat-eater.
Classification and history
Image:Apatosaurus2.jpg In 1877, Othniel Charles Marsh published notes on his discovery of Apatosaurus ajax, and then in 1879 described another, more complete dinosaur species, which he speculated to represent a new genus and named 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 mistakenly placed on its body.
Fossils of this animal have been found in Nine Mile Quarry and Bone Cabin Quarry in Wyoming, and at sites in Colorado, Oklahoma, Utah, USA.
Species
- A. ajax is the type species of the genera, and was named by the paleontologist Othniel Charles Marsh in 1877 after Ajax, the hero from Greek mythology. It is the holotype for the genera, 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.
Physiology
With such a huge 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, its 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
Obviously, its respiratory system could not have been reptilian; 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: multiple air sacs and a one-way 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.
Reference
See also
es:Apatosaurus fr:Brontosaure it:Apatosaurus he:אפאטוזאור nl:Apatosaurus ja:アパトサウルス no:Apatosaurus pl:Apatozaur pt:Apatossauro sk:Apatosaurus fi:Apatosaurus sv:Apatosaurus uk:Апатозавр zh:迷惑龙