Allosaurus is a genus of theropod dinosaur that lived in what is now North America during the Late Cretaceous period, about 70 million years ago. It was one of the largest meat-eating dinosaurs known to science and has been described as “the most fearsome predator ever to walk the Earth.”
The name allosaurid means “other lizard”, from Ancient Greek ἄλλ
Discovery and history
The first described fossil in this story is a bone obtained secondhand in 1869 by Ferdinand Vandeveer Haydn, who found it while prospecting in Middle Park, near Granbv, Colorado. He sent it to Joseph Leidy, whose work on dinosaurs began in 1856, and who identified it as half a tail vertebra, assigning it to the European dinosaur genera Poekilopleuron. In 1874, Richard Swann Lull published a description of the same specimen, naming it Trachodon gracilis, and describing it as a member of the family Troodontidae.
In 1876, Charles W. Gilmore named it Dryptosaurus gracilis, based on the locality where he found it; it became known as “Gracile Dragon”, and later as Allosaurus fragilis.
A few months later, Edward Drinker Cope renamed it Trachodon, and added the species name gracilis to the specific epithet. This name was soon changed to Poekilopleuron gracilis, in reference to the fact that the original type specimen was found in the middle part of the state of Colorado.
In 1888, Othniel Charles Marsh discovered the skeleton of another Allosaurus in New Jersey, and called it Camptosaurus dispar. In 1889, Henry Fairfield Osborn named the genus Allosaurus, and gave it the specific epithet dispar. A third specimen
The Cleveland-Lloyd dinosaur quarry in Emery County, UT, was discovered by W. E. “Bill” Stokes in 1945. During his lifetime he collected over 50 specimens, including many skeletons, skulls, teeth, and eggs. In addition to the fossils found here, Stokes’ collections are housed at the Museum of the Rockies in Bozeman, MT.
In 1960, the University of California Berkeley began excavating the site, and it continued under that university’s direction until 1964. More than 3,500 bones were recovered during those four seasons, including several partial skeletons.
After the UC Berkeley project concluded, the National Park Service took over the operation, and it continues today. Between 1960 and 1965, some 3,600 bones were recovered, including a complete skeleton of a young adult duckbill dinosaur, a juvenile ceratopsian, and a number of sauropodomorphs.
Recent work: 1980s–present
The period since Madsen’s book has seen a great expansion in studies covering topics concerning Allosaurus in both paleontology and paleoecology. Topics include skeletal variation, growth, anatomy, physiology, ecology, behavior, and even reproduction.
“Big Al” and “Big Al II”
In 1991, “Big Al”, a 95% complete, partly articulated specimen of Allosaurus, was discovered in southern Alberta, Canada. At the time it was one of the most complete specimens ever found. It measured about 8 metres (26 feet) long.
The discovery occurred during the summer of 1990, when a group of geologists working for the Royal Tyrrell Museum of Paleontology discovered what turned out to be a large bone sticking out of a hillside. They had been searching for fossils since 1985, and had never seen anything like this before. When they dug into the area around the bone, they uncovered a whole dinosaur graveyard.
They took samples of the bones and sent them off to Dr. John Ostrom, who was studying dinosaurs for the Smithsonian Institution. He recognized some of the bones as belonging to a type of dinosaur called Allosaurus, and he told his colleagues at the museum.
A few months later, the team returned to the site and began digging up the rest of the bones. They eventually unearthed over 2,500 pieces. These included skulls, vertebrae, ribs, limb bones, tail fragments, and even tiny teeth.
This find was important because it showed how many different types of animals lived together at the same time. For example, there were small carnivores such as foxes and coyotes, along with big herbivorous mammals such as camels, horses, giraffes, elephants, rhinos, and hippos. There were also plants such as ferns, horsetails, cycads, conifers, and flowering plants. And there were reptiles including lizards, snakes, turtles, crocodiles, and birds.
The bones were carefully packed away, and taken to the Royal Tyrrell Museum where they are still kept today. Over the next couple of decades, scientists studied the bones and learned much about the life of the ancient creatures.
One thing they noticed was that the Allosaurus skeletons were very similar to each other. In fact, they looked almost identical. But they weren’t exactly the same. One of them differed slightly from the others. Scientists named this particular specimen “Big Al”.