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10 Facts About Allosaurus

The Truth About the Jurassic Period's Most Dangerous Dinosaur



Allosaurus constantly grew and shed its teeth throughout its lifetime, like a shark (Oklahoma Museum of Natural History)


Allosaurus appeared on the scene tens of millions of years before T. Rex, and was the apex predator of the Jurassic period (Sergio Perez(


This early depiction of Allosaurus reflects the then-current views of paleontologists (Wikimedia Commons)

Allosaurus was the all-purpose carnivorous dinosaur of the late Jurassic period, and is especially well understood by paleontologists thanks to its numerous fossil remains. Here are 10 facts you may or may not have known about this fearsome meat-eater. (See also a gallery of Allosaurus pictures.)

1. Allosaurus used to be known as Antrodemus.

After it was discovered in the late 19th century, Allosaurus bounced around a bit in the classification bins. This dinosaur was first named Antrodemus (Greek for "body cavity") by the famous paleontologist Joseph Leidy, after an obscure anatomical feature, and was only systematically referred to as Allosaurus ("different lizard") starting in the mid-1970's. (See more about the discovery and naming of Allosaurus.)

2. Allosaurus may have preyed on Stegosaurus.

Paleontologists have unearthed solid evidence that Allosaurus preyed on (or at least occasionally tussled with) Stegosaurus: an Allosaurus vertebra with a puncture wound that matches the shape of a Stegosaurus tail spike (or "thagomizer"), and a Stegosaurus neck bone bearing an Allosaurus-shaped bite mark. (For a description of this battle, see Allosaurus vs. Stegosaurus - Who Wins?)

3. The typical Allosaurus lived for about 25 years.

Estimating a dinosaur's life span is always a tricky matter, but based on the voluminous fossil evidence, paleontologists believe Allosaurus attained its full adult size by age 15 (and was thus no longer vulnerable to predation). Barring disease, starvation or thagomizer wounds from angry stegosaurs, this dinosaur may have been capable of living another 10 or 15 years.

4. Allosaurus was one of the instigators of the "Bone Wars."

In their zeal to one-up one another, the 19th-century paleontologists Othniel C. Marsh and Edward Drinker Cope sometimes "diagnosed" new dinosaurs based on too-scanty evidence. Marsh had the honor of coining the genus Allosaurus, but both he and Cope went on to name other, supposedly new dinosaurs that (on further examination) turned out to be separate Allosaurus species.

5. "Big Al" is the most famous Allosaurus fossil.

It was only in 1991--after a full century of Allosaurus discoveries--that researchers unearthed an exquisitely preserved, near-complete fossil, which they promptly dubbed "Big Al." Unfortunately, Big Al didn't live a very happy life: analysis of its bones reveals numerous fractures and bacterial infections, which doomed this 26-foot-long teenaged dinosaur to a relatively early death.

6. Allosaurus regularly shed and replaced its teeth.

Like many predatory dinosaurs (not to mention modern crocodiles), Allosaurus constantly grew, shed and replaced its teeth, some of which averaged three or four inches in length (this dinosaur had about 16 teeth, in both its upper and lower jaws, at any given time). For this reason, it's possible to buy real, fossilized Allosaurus teeth for reasonable prices--only a few hundred dollars each!

7. Allosaurus comprised at least seven separate species...

As mentioned above, the early history of Allosaurus is littered with supposedly "new" dinosaurs that turned out, on further examination, to be separate Allosaurus species. To date, seven species (chief among them Allosaurus fragilis) have been more-or-less accepted by paleontologists, with a dozen or so more considered dubious at best; even still, one suspects that most experts would be happy with just A. fragilis.

8. ...one of which may or may not have been Saurophaganax.

Saurophaganax (Greek for "greatest lizard eater") was a 40-foot-long, two-ton theropod that lived alongside Allosaurus in late Jurassic North America. Pending further fossil discoveries, paleontologists haven't yet decided whether this dinosaur deserves its own genus, or is more properly classified as a new Allosaurus species, Allosaurus maximus.

9. There's no evidence that Allosaurus hunted in packs.

Paleontologists have long speculated that the only way Allosaurus could have preyed on the huge sauropods of its day was if it hunted in cooperative packs. It's a pretty picture, and it would make for a great Hollywood movie, but the fact is that even modern big cats don't team up to bring down full-grown elephants--so Allosaurus individuals probably hunted smaller prey on their own.

10. Allosaurus was one of the first dinosaur movie stars.

The Lost World, produced in 1925, was the first full-length dinosaur movie--and it starred not Tyrannosaurus Rex, but Allosaurus (not to mention Pteranodon and Brontosaurus, the dinosaur later renamed Apatosaurus). It was only a decade or so later, during the King Kong era, that T. Rex supplanted Allosaurus as Hollywood's famous meat-eating dinosaur.

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