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Apatosaurus ajax

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"deceptive lizard"

Describer Marsh, 1877
Also Known As Brontosaurus (Marsh, 1879), Elosaurus (Peterson and Gilmore, 1902)
Type of Species ajax
Order Saurischia
SubOrder Sauropodomorpha
InfraOrder Sauropoda
Micro-Order --
Family Diplodocidae
Size 70-90 feet (21-27 meters) in length
Period Late Jurassic, Kimmeridgian Tithonian
Fossilsite Morrison Formation, Colorado Wyoming, US
Diet Quadrupedal Herbivore

Apatosaurus is one of the best known of all dinosaurs but usually by its more popular name "Brontosaurus". Even though not quite the biggest of all when compared to Antarctosaurus, Seismosaurus, Supersaurus, and Ultrasaurus, was still an enormous, quadripedal, herbivore dinosaur. It was a member of the diplodocid family of long necked sauropods with whip like tails.

Its 20-foot-long neck supported a rather small head and its brain was about the size of a large apple. Two low ridges ran the length of its backbone, from the base of its skull almost to the tip of its tail. These spines supported the ligaments that held up the neck and tail. Apatosaurus' 30-foot whip-like tail, and its enormous size was probably its means of self-defense. This dinosaur lived in western North America, where most specimens have been recovered.

Apatosaurus ajax
Image courtesy of Todd Marshall

An American paleontologist Othniel C. Marsh described and named Apatosaurus in 1877. A few years later, in 1879, he described and named another dinosaur fossil, Brontosaurus ("thunder lizard"). It turned out that the two dinosaurs were actually two species of the same genus. The earlier scientific name, Apatosaurus, was retained, and the name Brontosaurus was no longer used.

Apatosaurus and some of the other large sauropods would have required to have large, powerful hearts, to sustain very high blood pressure, in Order to deliver blood to their small brains. The head of Apatosaurus was held high above its heart. This presents a problem in blood-flow physiology. To sustain this tremendous high blood pressure, an animal this size would of required to have wide, muscular blood vessels with many valves to prevent back flow of blood. Apatosaurus' blood pressure was probably over 400 mm Mercury, three or four times as high as ours.

Discovered Species
Apatosaurus ajax - Colorado
Apatosaurus excelsus - Oklahoma, Utah, and Wyoming
Apatosaurus louisae -Colorado
Apatosaurus yahnahpin - Wyoming

Apatosaurus was named in 1877 by US paleontologist Othniel C. Marsh. It was called Apatosaurus, which means "deceptive lizard," because its fossils were so similar to those of other sauropods. The first relatively complete Apatosaurus fossil was found by Earl Douglass in the Morrison Formation in Colorado, USA.

Albertosaurus sarcophagus Paleo Gallery
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Apatosaurus ajax

Apatosaurus ajax