The Giant Carnivorous Jurassic Dinosaur Allosaurus Was a Scavenger, Not a Predator

New research from Portland State University sheds light on the diets of the Late Jurassic dinosaur Allosaurus.

In a paper published on August 23, 2021, in the journal Ecological Modelling, authors Cameron Pahl and Luis Ruedas, of Portland State University, show that Allosaurus, a large carnivorous dinosaur from the Jurassic that has long been thought to be a top predator, could probably have acquired most of its calories by scavenging on the carcasses of enormous sauropod herbivores that lived alongside it. Pahl noted that “This new perspective may overturn 150 years of established thought.”

Allosaurus were contemporary in time and space with some of the largest herbivorous dinosaurs ever recorded.  These would have included well-known dinosaurs such as Camarasaurus, Barosaurus, Apatosaurus, Diplodocus, Brontosaurus, Supersaurus, and Brachiosaurus.  Brachiosaurus in particular once was considered the largest land animal to have ever lived and could have been up to 70 feet long and 64 tons in weight.  Supersaurus were over 110 feet in length and weighed up to 40 tons.  If these giant dinosaurs died primarily of natural causes, such as disease, starvation, and exhaustion, as is typical of many modern herbivore populations, their carcasses would have been plentiful enough to sustain viable populations of Allosaurus even without these undertaking any predatory behaviors. 

The researchers supported this hypothesis with a robust agent-based model, which simulated the relationship between carrion resources (carcasses) present in the Morrison Formation generated from the deaths of these sauropods, and the food energy requirements of Allosaurus. They further examined morphological attributes of the skull, including the extent of binocular vision in predators versus scavengers, as well as ecological data from fossils, such as relative population numbers in predators, herbivores, and scavengers.  The relative fragility of the skull and dentition of Allosaurus had already cast doubt on Allosaurus being a predator.  In addition to this shortcoming, Allosaurus did not have the binocular vision required to be a successful predator: it was only 30% that of T. rex, and 15% that of a modern lion’s. 

Allosaurus is a type of dinosaur dating from the Late Jurassic (Morrison Formation, 155 to 145 million years ago), that lived primarily in what is now Western North America.  Allosaurus were large bipedal dinosaurs in the theropod group, which also included Tyrannosaurus rex.  Indeed, Allosaurus bore some superficial resemblance to T. rex: Allosaurus were the largest meat-eating dinosaurs of their time and location, reaching up to 32 feet and weighing up to 2½ tons (with some estimates up to 4 tons).  They walked bipedally, had a large head, and jaws filled with long, sharp, serrated teeth that were easily shed and continuously replaced.  Also like T, rex, they had small upper arms and hands.  Together, these characteristics and the superficial similarities to T. rex led to Allosaurus being thought of as the top predator of the Morrison Formation.

All the facts therefore jointly point to Allosaurus having an ecological role of scavenger, similar to today’s vultures, rather than being an active predator, upending years of established thought.

Reference: “Carnosaurs as Apex Scavengers: Agent-based simulations reveal possible vulture analogues in late Jurassic Dinosaurs” by Cameron C. Pahl and Luis A. Ruedas, 21 August 2021, Ecological Modelling.
DOI: 10.1016/j.ecolmodel.2021.109706

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  • Coelophysis

    Allosaurus binocular vision is the same as the greatest dinosaur the most successful dinosaur ever the gator.early mesoeucrocodylia had binocular vision they are not alive any more only gator vision is alive .allosaurus has the best arm movement of any dinosaur that help if it is a grasping predator which allosaurus was .allosaurus improve there runner they have hooves like fast mammal if they were scavenger the will not improve running allso gator type land mesoeucrocodylia allso evolve hooves i here no won call them scavenger I never herd of a scavenger mesoeucrocodylia allosaurus has unique neck joints and have simular unique skull predator feature as t.rex gator not as advance as t.rex gator allso that thing over the eye the top of the skull that allso found in fossil mesoeucrocodylia but it was not over the eyes were the temporal fenestra is the top of the skull that were it is .allosaurus is a tetanuran dinosaur like the gator .the trend in tetanuran dinosaur is getting faster they evolve furcula because they were quadrupedal predator all thou quadrupedal was a joke only use for launching bipedal and was not use all the time most land predator are crouching animal allso wait on the ground like a house cat . The reason why t.rex lost its finger only 2 now because it’s not a grasping predator because of stronger skull because speed is the game in modern crocodilian. t.rex finger is a quadrupedal finger it’s like finger of lizard that change color there gait is like mammal not sprawling and carntosaurus finger is same way but it has 4 finger and is not a tetanuran .that why carntosaurus finger fuse so it looks like t.rex fingers it’s convergent evolution .carntosaurus elbow is fuse clearly they are not grasping predator .the grasping finger is slow when running quadrupedal that why these dinosaur got rid of those grasping finger but they are still quadrupedal running but faster .dinosaur were very fast animal is so violent fast they developed furcula so legs do not break simular to bird wings .that why gator develope bird flight feature advance pectoral girdle even thou they have those monster centra backbone joint .dinosaur arms are very robust.head killer dinosaur change the finger.I think carntosaurus is clawless if my memory is right .tetanuran allso have speedy stiff tail .

  • DurkyB

    Swear to God, every carnivore in the history of carnivorous creatures, in one shape or form, can be called a scavenger. Every carnivore is an opportunistic eater. It only makes sense? I mean, do you see people out and about killing animals every day to survive? No, no you don’t. Most people in our society would absolutely die if they had to fend for themselves in terms of living off the land. My point being, every carnivore has scavenged for food at one point or another. It’s called surviving. I’m sure the allosaurus was just like other large therapod dinosaurs. Hunted in packs to take down big game, wouldn’t pass up an easy meal, and I’m sure some preferred to be alone so they hunted alone and primarily scavenged what they could. Again, it’s called survival. We see homeless people and animals do it every day digging through the trash for scaps. It’s not about the meal you settle with today, it’s living to see the better meal tomorrow. To say the allosaurus was nothing but a scavenger and not a hunter is a pretty hollow statement. I mean, why else would evolution have given it the tools it needed to take down prey?