The Large, Meat-Eating Dinosaurs - Allosaurs, Carnosaurs, and Their Friends

The Large, Meat-Eating Dinosaurs of the Later Mesozoic Era

Acrocanthosaurus, one of the largest theropods of the early Cretaceous period (Dmitry Bogdanov).

Few issues in paleontology are as confusing as the classification of theropods--the bipedal, mostly carnivorous dinosaurs that evolved from archosaurs during the late Triassic period and persisted until the end of the Cretaceous (when the dinosaurs went extinct). The problem is, theropods were extremely numerous, and at a distance of 100 million years it can be hard to distinguish one genus from another based on fossil evidence, much less to determine their evolutionary relationships.

(See a gallery of large carnivorous dinosaur pictures.)

For this reason, the way paleontologists classify theropods is in a state of constant flux. So, I'm going to add fuel to the Jurassic fire by creating my own informal sorting system. I've already addressed tyrannosaurs, raptors, therizinosaurs, ornithomimids and "dino-birds"--the more evolved theropods of the Cretaceous period--in separate articles on this site. This piece will mostly discuss the "big" theropods (excluding tyrannosaurs and raptors) that I've dubbed the 'saurs: allosaurs, ceratosaurs, carnosaurs, and abelisaurs, to name just four sub-classifications.

Here are brief descriptions of the classifications of large theropods currently in (or out of) vogue:

Abelisaurs. Sometimes included under the ceratosaur umbrella (see below), abelisaurs were characterized by their large sizes, short arms, and (in a few genera) horned and crested heads.

What makes the abelisaurs a useful group is that they all lived on the southern supercontinent of Gondwana, hence the numerous fossil remains found in South America and Africa. The most notable abelisaurs were Abelisaurus (of course), Majungatholus and Carnotaurus.

Allosaurs. It probably won't seem very helpful, but paleontologists define an allosaur as any theropod more closely related to Allosaurus than to any other dinosaur (a system that applies equally well to all the theropod groups listed below; just substitute Ceratosaurus, Megalosaurus, etc.) In general, allosaurs had large, ornate heads, three-fingered hands, and relatively large forearms (compared to the tiny arms of tyrannosaurs).

Examples of allosaurs include Carcharodontosaurus, Giganotosaurus and the huge Spinosaurus.

Carnosaurs. Confusingly, the carnosaurs (Greek for "flesh-eating lizards") includes the allosaurs, above, and is sometimes taken to embrace the megalosaurs (below) as well. The definition of an allosaur pretty much applies to a carnosaur, though this broader group includes such relatively small (and sometimes feathered) predators as Sinraptor, Fukuiraptor and Monolophosaurus. (Oddly enough, as yet there's no genus of dinosaur named Carnosaurus!)

Ceratosaurs. This designation of theropods is in even greater flux than the others on this list. Today, the ceratosaurs are defined as early, horned theropods related to (but not ancestral to) later, more evolved theropods like tyrannosaurs. The two most famous ceratosaurs are Dilophosaurus and, you guessed it, Ceratosaurus.

Megalosaurs. Of all the groups on this list, megalosaurs are the oldest and least respected. This is because, early in the 19th century, pretty much every new carnivorous dinosaur was assumed to be a megalosaur, Megalosaurus being the first theropod ever officially named (before the word "theropod" was even coined). Today, megalosaurs are rarely invoked, and when they are, it's usually as a subgroup of carnosaurs alongside the allosaurs.

Tetanurans. This is one of those groups that's so all-inclusive as to be practically meaningless; taken literally, it includes everything from carnosaurs to tyrannosaurs to modern birds. Some paleontologists consider the first tetanuran (the word means "stiff tail") to have been Cryolophosaurus, one of the few dinosaurs to be discovered in modern Antarctica.

Next page: the Behavior of Large Theropods, and a List of Notable Genera

The Behavior of Large Theropods

As with all carnivores, the main consideration driving the behavior of large theropods like allosaurs and abelisaurs was the availability of prey. As a rule, carnivorous dinosaurs were much less common than herbivorous dinosaurs (since it requires a large population of herbivores to feed a smaller population of carnivores). Since some of the hadrosaurs and sauropods of the Jurassic and Cretaceous periods grew to extreme sizes, it's reasonable to conclude that even the bigger theropods learned to hunt in packs of at least two or three members.

One major topic of debate is whether large theropods actively hunted their prey, or feasted on already dead carcasses. Although this debate has crystallized around Tyrannosaurus Rex, it has ramifications for smaller predators like Allosaurus and Carcharodontosaurus as well. Today, the weight of the evidence appears to be that theropod dinosaurs (like most carnivores) were opportunistic: they chased down juvenile sauropods when they had the chance, but wouldn't turn up their noses at a huge Diplodocus that died of old age.

Hunting in packs was one form of theropod socialization, at least for some genera; another may have been raising young. The evidence is sparse at best, but it's possible that larger theropods protected their newborns for the first couple of years, until they were big enough not to attract the attention of other hungry carnivores. (However, it's also possible that some theropod kids were left to fend for themselves from birth!).

Finally, one aspect of theropod behavior that has received a lot of attention in the popular media is cannibalism. Based on the discovery of the bones of some carnivores (such as Majungasaurus) bearing the tooth marks of adults of the same genus, it's believed that some theropods may have cannibalized their own kind.

Despite what you've seen on TV, though, it's much more likely that the average allosaur ate its already-dead family members rather than actively hunting them down for an easy meal!

Here's a list of the best-known large theropods of the Mesozoic Era; just click on the links for more information.

Abelisaurus "Abel's lizard" has been recontructed from a single skull.

Afrovenator One of the few carnivores ever to be dug up in northern Africa.

Allosaurus One of the most common predators of the Jurassic era.

Baryonyx Long story short: you wouldn't want to clip this dino's claws.

Carcharodontosaurus Its name means "great white shark lizard." Impressed yet?

Carnotaurus The shortest arms of any meat-eater--and horns to match.

Ceratosaurus This primitive carnivore is hard to classify.

Concavenator This large theropod had a bizarre hump on its back.

Cryolophosaurus This crested carnivore was once known as "Elvisaurus."

Edmarka This may have been a species of Torvosaurus.

Ekrixinatosaurus Its name means "explosion-born lizard."

Eustreptospondylus A close cousin of Megalosaurus.

Fukuiraptor One of the few carnivorous dinosaurs ever to be dug up in Japan.

Gasosaurus Yes, that's its real name, and not for the reason you think.

Giganotosaurus Not quite a "Gigantosaurus," but close enough.

Gojirasaurus This early predator was named after Godzilla.

Ilokelesia A primitive abelisaur from South America.

Indosuchus This "Indian crocodile" was actually a dinosaur.

Kaijiangosaurus This might have been the same dinosaur as Gasosaurus.

Lourinhanosaurus This hard-to-classify theropod was discovered in Portugal.

Majungatholus Fairly--or unfairly--known as the "cannibal dinosaur."

Megalosaurus The first dinosaur ever to be discovered and named.

Megaraptor Despite its name, it wasn't really a true raptor.

Monolophosaurus This Jurassic predator had a single crest on its skull.

Noasaurus Were this predator's giant claws on its hands, or on its feet?

Piatnitzkysaurus Its teeth were as sharp as its name is funny.

Poekilopleuron It may (or may not) have been a species of Megalosaurus.

Rajasaurus This "prince lizard" lived in what is now modern-day India.

Rugops This wrinkly-faced carnivore probably fed on abandoned carcasses.

Siamotyrannus Despite its name, it wasn't a true tyrannosaur.

Sinraptor Despite its name, this allosaur wasn't any better or worse than other dinosaurs.

Spinosaurus This dino was distinguished by the sail-like structure on its back.

Suchomimus A fish-eater with a distinctly crocodilian profile.

Torvosaurus One of the largest predators of Jurassic North America.

Tyrannotitan We know very little about this fearsomely named dinosaur.

Xenotarsosaurus A poorly understood abelisaur from South America.

Xuanhanosaurus You didn't think there'd be an "X" on this list, did you?