Apatosaurus
A large, long-necked sauropod with a whip-like tail.
Known for its long neck, whip-like tail, and robust build, *Apatosaurus* is one of the most iconic dinosaurs, though its skull was long misidentified and mounted with that of *Camarasaurus* until the 1970s. This herbivorous sauropod lived in North America during the Late Jurassic, approximately 152 to 151 million years ago, and its fossils have been found in the Morrison Formation across modern-day Colorado, Oklahoma, New Mexico, Wyoming, and Utah. The first species, *Apatosaurus ajax*, was named by Othniel Charles Marsh in 1877, with a second, *Apatosaurus louisae*, described by William H. Holland in 1916. The genus name means "deceptive lizard," a reference to early confusion over its remains. *Apatosaurus* was a member of the diplodocid family, distinguished from *Diplodocus* by its stouter cervical vertebrae and more robust leg bones, making it a heavier, more powerfully built animal. Its tail was held off the ground during normal movement, and it had a single claw on each forelimb and three on each hindlimb. The skull, once thought to resemble that of *Camarasaurus*, is actually closer to *Diplodocus* in form. To lighten its massive vertebrae, *Apatosaurus* had internal air sacs that created numerous hollow spaces. Its tail may have been used as a whip to produce loud sounds or, as more recently suggested, as a sensory organ. The confusion over its skull persisted until the 1909 discovery of a complete *A. louisae* skull near the neck of its holotype, though Henry Fairfield Osborn disagreed and mounted an *Apatosaurus* skeleton with a *Camarasaurus* skull cast. It was not until 1970 that researchers demonstrated that more robust skulls assigned to *Diplodocus* likely belonged to *Apatosaurus*. Within the diplodocid family, *Apatosaurus* is considered a relatively basal genus, with only *Amphicoelias* and possibly an unnamed genus being more primitive. The subfamily Apatosaurinae, named in 1929, was not used validly until a 2015 study, which placed only *Brontosaurus* alongside *Apatosaurus*; *Brontosaurus* had long been considered a junior synonym of *Apatosaurus* but was revived as a valid genus by that study, though not all paleontologists agree. In its Late Jurassic habitat, *Apatosaurus* coexisted with dinosaurs such as *Allosaurus*, *Camarasaurus*, *Diplodocus*, and *Stegosaurus*.
- average_length
- 21–23 m (69–75 ft)
- average_mass
- 16.4–22.4 t (16.1–22.0 long tons; 18.1–24.7 short tons)
- maximum_mass
- approximately 33 t (32 long tons; 36 short tons)
- diet
- herbivorous
- family
- Diplodocidae
Lore & Background
Fossils of *Apatosaurus* have been found in the Morrison Formation of modern-day Colorado, Oklahoma, New Mexico, Wyoming, and Utah. This large, long-necked, quadrupedal herbivore had a long, whip-like tail and forelimbs slightly shorter than its hindlimbs. Its skull was small relative to its body, with a squared snout and spatulate teeth suited for browsing. The neck vertebrae were deeply bifurcated, with a trough in the middle, and were stouter and more robust than those of other diplodocids, supporting a neck that was nearly triangular in cross-section. The vertebral column included fifteen cervical, ten dorsal, five sacral, and eighty-two caudal vertebrae, though the tail bone count could vary. The dorsal ribs were loosely articulated rather than fused. To lighten its skeleton, the vertebrae contained extensive air sacs, making the bones internally full of holes. The animal had a single claw on each forelimb and three on each hindlimb. Its tail was held above the ground during normal locomotion and may have been used as a whip to create loud noises or as a sensory organ. The skull was long confused with that of *Camarasaurus* and *Brachiosaurus* until a complete skull was found near the holotype of *A. louisae* in 1909, though some mounted skeletons continued to use incorrect skull casts until the 1970s. *Apatosaurus* lived alongside dinosaurs such as *Allosaurus*, *Camarasaurus*, *Diplodocus*, and *Stegosaurus*.
Reader's Guide
Apatosaurus is a member of the diplodocid family, differing from Diplodocus in its more robust cervical vertebrae and leg bones. Its neck vertebrae are less elongated and more heavily constructed, and its leg bones are stockier, implying a more robust animal. The tail was held above the ground during normal locomotion and may have been used as a whip to create loud noises or as a sensory organ. Apatosaurus had a single claw on each forelimb and three on each hindlimb. The genus is considered one of the more basal diplodocids, with only Amphicoelias and possibly a new, unnamed genus more primitive. Apatosaurus lived alongside Allosaurus, Camarasaurus, Diplodocus, and Stegosaurus.
Did You Know?
- Apatosaurus means 'deceptive lizard'.
- Apatosaurus had air sacs that made its vertebrae internally full of holes to lighten the skeleton.
- Some specimens of A. ajax may have reached lengths of 30 m (98 ft) and masses of 33 t (36 short tons).
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