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Allosaurus sp. (theropod dinosaur femur bones) (Morrison Formation, Upper Jurassic; Cleveland-Lloyd Dinosaur Quarry, Emery County, Utah, USA) 1 | by James St. John
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Allosaurus sp. (theropod dinosaur femur bones) (Morrison Formation, Upper Jurassic; Cleveland-Lloyd Dinosaur Quarry, Emery County, Utah, USA) 1

Allosaurus sp. - theropod dinosaur femur bones from the Jurassic of Utah, USA. (public display, Cleveland-Lloyd Dinosaur Quarry, Utah, USA)


The Upper Jurassic Morrison Formation is widely distributed in many western American states. The unit consists of fluvial (river/floodplain) and lacustrine (lake) deposits. Dinosaur bones and dinosaur tracks are moderately common in Morrison Formation sediments. Exceptionally dinosaur-rich localities include Como Bluff in Wyoming, Dinosaur National Monument in Utah, Dinosaur Ridge in Colorado, and the Cleveland-Lloyd Quarry in Utah.


Seen here is an ontogenetic series of Allosaurus femur bones from the Cleveland-Lloyd Quarry. Allosaurus is a theropod, a group of small to large, bipedal dinosaurs. Almost all known members of the group were carnivorous (predators and/or scavengers). They represent the ancestral group to the birds, and some theropods are known to have had feathers.


From exhibit signage:


The Mighty Allosaurus


Top of the Food Chain

Allosaurus was the most common large meat eater of its time. It had strong bones and powerful muscles and its size enabled it to attack dinosaurs even larger than itself. Most of the allosaurs from the Cleveland-Lloyd Dinosaur Quarry are juvenile or adolescent in age.


Quick Killers

Like all theropod dinosaurs, Allosaurus walked on two legs. Its arms were much weaker than the legs, but remained formidable weapons. Each of the three fingers, including an opposable digit, terminated in a sharp claw, making them perfect for grabbing, cutting, and slashing prey.


Its name means 'other' or 'different' lizard. While not a lizard, it was certainly different from all other dinosaurs of its time.


A Cutting Bite

The skull of Allosaurus has mighty jaws lined with about 60 dagger-like teeth. Like steak knives, the curved teeth were serrated to slice quickly and deep into the flesh of prey. When one tooth fell out, a new one would grow in. Its jaws were moved by powerful muscles that passed through the back of the skull to the top of its head.


Physical Characteristics

An adult Allosaurus had a head that was over three feet in length, which required a power neck. The pointed bony crests above each of the eyes may have been used during mating display and for species recognition.


Hunters and Scavengers.

Some scientists think that such great size may have hindered Allosaurus, making it too clumsy to effectively hunt and pursue prey and forcing it to scavenge for carcasses. Others point out that much of the potential prey was also large and slow, so fresh meat could remain on the menu.


The Leader of the Pack?

Some paleontologists believe [sic] that Allosaurus may have been quite fast over short distances. This may have allowed for the ambush of other dinosaurs by a group or pack of allosaurs.


As the Bones Grow

The Cleveland-Lloyd Dinosaur Quarry presents a great opportunity for ongoing research. Paleontologists are studying the development of dinosaurs as they matured. As dinosaurs grow, their bones not only become longer - their shapes change as well.


An Allosaurus thigh bone (femur) became sturdier and stronger as the dinosaur aged. Its cross-section changed from round to oval. This indicates that young dinosaurs' legs extended to the sides, and older dinosaurs' legs were directly beneath the body.


The ratio of femur length to body size became smaller as the animal grew. In this way, Allosaurus was unlike modern reptiles and more like modern "warm blooded" animals such as mammals and birds.


Classification: Animalia, Chordata, Vertebrata, Dinosauria, Saurischia, Theropoda, Allosauridae


Stratigraphy: Morrison Formation, Upper Jurassic


Locality: Cleveland-Lloyd Dinosaur Quarry, Emery County, Utah, USA


See info. at:



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Taken on June 23, 2007