The Apatosaurus, meaning “deceptive lizard,” was one of the most massive sauropod dinosaurs. This gigantic herbivore belonged to a group of long-necked, four-legged dinosaurs that dominated the landscape during the Jurassic period. Its sheer size and the long-standing confusion surrounding its name have made it a fascinating subject of both paleontology and popular culture.
Physical Characteristics and Scale
The Apatosaurus was a member of the Diplodocidae family, a group characterized by their immense size and long, slender build. An average adult reached lengths of approximately 69 to 75 feet (21 to 23 meters) from head to tail tip. Weight estimates for these behemoths generally range between 16.4 and 22.4 tons, though some of the largest individuals may have weighed over 40 tons.
The dinosaur’s neck was thick and powerful, featuring heavily constructed vertebrae compared to its close relative, Diplodocus, suggesting a more robust overall animal. Its body was supported by four massive, pillar-like legs, with the forelimbs slightly shorter than the hindlimbs. A distinguishing feature was its incredibly long, whip-like tail, which could measure up to 50 feet and may have been used for defense against predators.
The feet were also notable, possessing a single large claw on each forelimb and three claws on the hindlimbs. Despite its size, the head was comparatively small, featuring a slender snout and chisel-like teeth suited for its diet. The sheer scale of the Apatosaurus meant that even a formidable predator like the Allosaurus would have struggled to attack a fully grown individual.
Diet and Geological Context
The Apatosaurus was a strict herbivore, relying on vast quantities of plant matter. Its spatulate, or chisel-like, teeth were arranged at the front of its jaws, making them suitable for stripping vegetation rather than chewing. The dinosaur likely functioned as a generalized browser, using its long neck to graze on low-lying plants and possibly reach medium-height foliage.
The Apatosaurus thrived during the Late Jurassic period, approximately 152 to 151 million years ago. This time placed it in an ecosystem rich with other massive dinosaurs, including Stegosaurus and Allosaurus. Nearly all known fossil specimens have been recovered from the Morrison Formation in western North America, a vast geological layer spanning modern-day states like Colorado, Utah, and Wyoming. This environment was semi-arid, featuring floodplains and lush riparian areas, and the Apatosaurus fed on abundant ferns, cycads, and conifers.
The Story of the Two Names
The historical confusion between Apatosaurus and Brontosaurus is a famous story in paleontology, originating from the competitive “Bone Wars” of the late 19th century. Paleontologist Othniel Charles Marsh first described and named Apatosaurus in 1877 based on an incomplete skeleton. Two years later, in 1879, Marsh named a larger, more complete skeleton Brontosaurus excelsus, believing it to be a new genus.
In 1903, paleontologist Elmer Riggs concluded that the differences between the two animals were not enough to warrant separate genera. The older name, Apatosaurus, was given priority and Brontosaurus was officially considered a junior synonym. This designation meant that all specimens were formally reclassified as Apatosaurus, though the name Brontosaurus remained popular with the public.
The scientific consensus was challenged in 2015 when a comprehensive study re-examined the Diplodocidae family. This analysis, which compared hundreds of skeletal features across multiple specimens, concluded that Brontosaurus possessed enough distinct anatomical differences to be reinstated as its own valid genus, separate from Apatosaurus. This finding successfully resurrected the iconic “thunder lizard” back into the scientific lexicon.