Theropod Dinosaurs

In the 1980 movie “The Mountain Men” Bill Tyler (Charlton Heston) and Henry Pratt (Brian Keith) the two crusty protagonists are camping out rough. There’s a sound from the dark: 

“There’s somethin’ out there.” says Henry. 

“Of course there’s somethin’ out there”, replies an exasperated Bill, “There’s always something out there!” 

And that has been the simple truth ever since the first life crawled out of the protean sea over 500 million years ago. There truly always is something out there, something that does not wish us well, something that we would rather not see up close and personal, in here with us. The late Triassic “something out there” was the apex predatory Archosaur, Postosuchus. By the end of the Cretaceous Tyrannosaurus rex would be the embodiment of terror that lurked in the shadows. 

But the Jurassic period belonged to the Allosaurs and their kin. Allosaurs are not generally considered to be heavyweights in the class of T. rex, a creature that stood nearly 20 feet tall and tipped the scales at 8 tons or like Giganotosaurus, taller by some accounts and possibly even heavier than the better known Tyrannosaur. This does not mean that the Allosaurs were minor leaguers. 

Allosaurus fragilus, the most widely collected and generally recognized species of Allosaur, averaged 28 feet in length with an average estimated weight of 2500 pounds. Larger specimens up to 32 feet in length and running to an estimated 5000 pounds have been found in the Morrison formation of the American West and Midwest. 

If the incompletely collected fossils of Epanterias amplexus turn out to be not a separate genus, as has been thought, but simply a large specimen of Allosaurus fragilus we are looking at a specimen nearly forty feet in length and weighing in at 6.8 tons or so, a predator on the truly grand scale. A specimen originally classified as Allosaurus maximus that ran to a bulky 36 feet in length has since been re classified as a separate but closely related genus, Saurophaganax. 

At the top of the food chain: 

Whether or not Allosaurs were the biggest, they were certainly the “baddest” predators in their late Jurassic time slot. The warm, tropical climate of the disintegrating super continent Pangaea provided lush cycads, ginkgos, conifers and ferns as fodder for Stegosaurs and Iguanodonts and huge and familiar sauropods like Diplodocus and Brachiosaurus. All of these could and would have been fair game for hungry Allosaurs. So, apparently would other Allosaurs. 

Fossil findings of groups of Allosaurus fragilus among fossils of sauropods lead to speculation that Allosaurs perhaps formed packs, and cooperated on the hunt. An equally valid point of view is that these aggregations merely indicate aggressive behaviors by lone Allosaurs upon one another, as they fought over possession of a kill, or scavenged carcass. Injuries on Allosaur fossils that appear to have been inflicted by other Allosaurs tend to support this hypothesis. 

Allosaurs enjoyed a long reign, enduring from the middle Jurassic until the early Cretaceous. They we widespread, fossils have been found in North America, Asia, Poland, Portugal and even Australia. Allosaur fossils are the most commonly discovered of the large Theropod dinosaurs. So while T rex and Giganotosaurus may get more attention, neither could match the Allosaur for distribution and staying power.