Apatosaurus: The Complete Guide to the Thunder Lizard

With its massive body, long neck, and whip‑like tail, Apatosaurus is one of the most iconic dinosaurs of the Jurassic. For decades, it was better known by another name: Brontosaurus. The story of how Apatosaurus was mistaken for a different dinosaur, then resurrected as its own genus, is one of the most famous tales in paleontology. But beyond its taxonomic history, Apatosaurus was a remarkable animal – a giant sauropod that roamed the floodplains of North America, consuming vast quantities of plants to fuel its enormous body.

In this comprehensive guide, we’ll explore everything about Apatosaurus: its size, anatomy, the function of its tail, its diet, and the fascinating story of its discovery and reclassification.

1. What is Apatosaurus?

Apatosaurus ajax is a genus of diplodocid sauropod dinosaur that lived during the Late Jurassic period, approximately 152 to 151 million years ago. Its name means “deceptive lizard” (from Greek apate “deception” and sauros “lizard”), referring to the confusing similarity of its tail vertebrae to those of another dinosaur. It is one of the most well‑known sauropods, largely because it was once mistakenly combined with Brontosaurus.

Apatosaurus belongs to the family Diplodocidae, which includes other giants like Diplodocus and Barosaurus. Its fossils have been found in the Morrison Formation of western North America (Colorado, Wyoming, Utah, and Oklahoma). It coexisted with other iconic dinosaurs such as Allosaurus, Stegosaurus, and Diplodocus.

2. Physical Characteristics: Size and Anatomy

Apatosaurus was a true giant. Here are its key measurements:

• Length: Up to 21–23 meters (69–75 feet).
• Height at hips: About 4.5–5 meters (15–16 feet).
• Weight: Estimated between 20 and 35 metric tons (22–39 short tons).
• Neck: Long but relatively short compared to Diplodocus, with 15 vertebrae.
• Tail: Long and whip‑like, with up to 80 caudal vertebrae.
• Skull: Small and low, with a toothless beak and peg‑like teeth only at the front of the jaws.
• Limbs: Hind limbs longer than forelimbs, giving the back a gentle upward slope.

Its skeleton was built to support immense weight. The vertebrae were hollow and filled with air sacs, reducing weight while maintaining strength. The limbs were column‑like, with broad feet. The front feet had a single claw on the thumb, while the hind feet had three claws. The skull was long and low, with nostrils placed high on the head.

3. The Whip Tail: Defense or Communication?

Like its relative Diplodocus, Apatosaurus had an extremely long, whip‑like tail. The tail was composed of up to 80 vertebrae, with the last third being slender and flexible. The tip could be moved at supersonic speeds, producing a loud crack similar to a bullwhip. This tail likely served multiple functions:

• Defense: A well‑aimed tail crack could deter predators like Allosaurus. The sound alone might have been enough to startle an attacker.
• Communication: The crack could have been used to signal other members of the herd across long distances.
• Intraspecific combat: Males may have used their tails to compete for mates, though direct evidence is lacking.

Fossilized tail vertebrae show fused tips, likely to withstand the stress of high‑velocity movements.

4. Diet: How Did It Eat?

Apatosaurus was a herbivore that fed on the abundant plants of the Jurassic. Its peg‑like teeth were restricted to the front of the snout, and they were not used for chewing. Instead, it likely:

• Stripped leaves and needles from branches by pulling them through its teeth.
• Swallowed food whole, using gastroliths (stomach stones) to grind plant material.
• Browsed at a height of about 3–5 meters (10–16 feet), though it could have reared up to reach higher vegetation.

Its diet likely consisted of conifers, ferns, cycads, and ginkgoes. The Morrison Formation preserved a diverse flora, providing ample food for these giant herbivores. Stable isotope studies suggest that Apatosaurus may have fed on a variety of plants, possibly including aquatic vegetation.

5. Growth and Variation

Apatosaurus grew rapidly, reaching adult size in about 15–20 years. Studies of bone histology show that juveniles grew quickly, with growth rates slowing as they neared maturity. Several species of Apatosaurus have been named, but only A. ajax and A. louisae are widely accepted. A. louisae is known from a nearly complete skeleton at the Carnegie Museum.

The famous “Brontosaurus” skeleton was originally based on a partial Apatosaurus skeleton with a Camarasaurus skull. This composite led to decades of confusion, eventually resolved when a complete Apatosaurus skull was found.

6. Habitat and Lifestyle: Where Did Apatosaurus Live?

Apatosaurus likely lived in herds, based on trackways and bone beds of related sauropods. Herding behavior would have provided protection against predators and helped them find food. They may have migrated seasonally, following the growth of vegetation.

7. Predators and Defense

The primary predator of Apatosaurus was Allosaurus, the most common large theropod in the Morrison Formation. Adult Apatosaurus were too large for a single Allosaurus to tackle, so predators likely targeted juveniles or sick individuals. Defense strategies included:

• Size: Adults were simply too massive to be threatened.
• Whip tail: A well‑aimed tail crack could injure or deter a predator.
• Herding: Group living allowed adults to protect young by forming a defensive circle.

There is no direct evidence of Allosaurus attacking Apatosaurus, but bite marks on sauropod bones from the Morrison Formation suggest that attacks did occur.

8. The Brontosaurus Saga: A Tale of Mistaken Identity

The story of Apatosaurus and Brontosaurus is one of the most famous in paleontology. In 1877, Othniel Charles Marsh named Apatosaurus ajax based on a partial skeleton. In 1879, he named Brontosaurus excelsus based on a more complete skeleton, which he mistakenly thought belonged to a different genus. In 1903, Elmer Riggs pointed out that Brontosaurus was actually a junior synonym of Apatosaurus, and the name was suppressed.

For over a century, the name Brontosaurus was considered invalid, but the public continued to use it. In 2015, a major study by Emanuel Tschopp and colleagues argued that Brontosaurus was distinct enough to be resurrected as a separate genus. This study, based on a comprehensive analysis of diplodocid anatomy, proposed that B. excelsus and B. parvus should be recognized as valid. The debate continues, but many paleontologists now accept Brontosaurus as a separate genus, though it remains closely related to Apatosaurus.

9. Discovery and Naming

The first Apatosaurus fossils were discovered in 1877 by Arthur Lakes in Colorado, working for Othniel Charles Marsh. Marsh named the genus Apatosaurus ajax in 1877. In 1879, Marsh named Brontosaurus excelsus from a more complete skeleton found in Wyoming. For decades, the two names coexisted until Elmer Riggs recognized they were the same animal in 1903, and the name Apatosaurus took priority.

In 1905, the American Museum of Natural History mounted the first complete sauropod skeleton, which they called Brontosaurus. This mount became an icon, cementing the name in popular culture. It wasn’t until the 1970s that the correct skull of Apatosaurus was identified and placed on the mount, ending the confusion.

10. Apatosaurus Gallery

Explore the thunder lizard

← Swipe or scroll to see more images →

Final Thoughts

Apatosaurus is a dinosaur that has captivated the public imagination for over a century, partly because of its fascinating taxonomic history. Whether you call it Apatosaurus or Brontosaurus, there is no denying that this sauropod was one of the most successful giants of the Jurassic. Its massive size, whip tail, and complex social behavior make it a fascinating subject of study. The ongoing debate over its name only adds to its enduring appeal.