Apatosaurus, also known by the popular but scientifically deprecated synonym Brontosaurus, is a genus of sauropod dinosaur that lived from about 154 to 150 million years ago, during the Jurassic Period (Kimmeridgian and early Tithonian ages). It was one of the largest land animals that ever existed, with an average length of 23 m (75 ft) and a mass of at least 23 metric tons (25 short tons). The composite term Apatosaurus comes from the Greek names apate (ἀπάτη)/apatelos (ἀπατηλός) meaning "deception"/"deceptive" and sauros (σαῦρος) meaning "lizard"; thus, "deceptive lizard".
Description
Apatosaurus was a large, long-necked quadrupedal animal with a long, whip-like tail. Its forelimbs were slightly shorter than its hindlimbs. One measurement places the total length of the species Apatosaurus louisae at 22 m (72 ft).
It was roughly the weight of four elephants. One specimen of A. excelsus was estimated to weigh 25,952 kg (57,210 lb); estimates for A. louisae were 20,600 kg (45,000 lb) and 22,407 kg (49,400 lb). Other estimates of the body mass of adult Apatosaurus species range from 18,000 kg (40,000 lb) to 35,000 kg (77,000 lb). A microscopic study of Apatosaurus bones concluded that the animals grew rapidly when young and reached near-adult sizes in about 10 years.
The skull was small in comparison with the size of the animal. The jaws were lined with spatulate teeth, which resembled chisels, suited to an herbivorous diet. Like other sauropods, the vertebrae of the neck were deeply bifurcated; that is, they carried paired spines, creating a wide and deep profile for the neck. The apparently massive neck was, however, filled with an extensive system of weight-saving air sacs. Apatosaurus, like its close relative Supersaurus, is notable for the incredibly tall spines on its vertebrae, which make up more than half the height of the individual bones. Also unusual among diplodocids is the shape of the tail, which is comparatively thin in breadth and short in height, a profile caused by the vertebral spines decreasing in height rapidly the farther they are from the hips. Apatosaurus also had very long ribs compared to most other diplodocids, giving it an unusually deep chest. The limb bones were also very robust.
Classification and Species
Apatosaurus is a member of the family 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, Supersaurus and Eobrontosaurus.
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 species, which he named Brontosaurus excelsus. In 1903, Elmer Riggs re-examined the fossils. While he agreed with Marsh that Brontosaurus excelsus was likely a distinct species, he also noted many similarities between B. excelsus and A. ajax, and decided that both should be placed in the same genus. Riggs re-classified the species as Apatosaurus excelsus. Almost all paleontologists since Riggs published his opinions have agreed that the two species should be classified together in a single genus. 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 is considered a junior synonym and has therefore been 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 Utah in the United States. Apatosaurus parvus was originally known as Elosaurus parvus, but was reclassified as a species of Apatosaurus in 1994.
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