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Acrocanthosaurus

After 120 million years of lying entombed in an ancient stream bed, not to mention more than a decade of excavation and preparation, the nearly forty foot long skeleton of the predatory dinosaur, Acrocanthosaurus atokensis is standing tall. “Even those of us involved in the preparation of this skeleton are awed by the sense of power we feel in the presence of the mounted skeleton.” explained Terry Wentz, chief preparator on the project, while showing the dinosaur to a visitor. This enormous carnivore was closely related to Carcharodontosaurus saharicus from Africa (newly found remains of this dinosaur were unearthed by Dr. Paul Sereno of the University of Chicago) and was nearly as large as Tyrannosaurus rex but lived more than 50 million years earlier.

  • Order: Saurischia
  • Suborder: Theropoda
  • Family: Allosauridae
  • Genus: Acrocanthosaurus
  • Species: atokensis
  • Pauluxy Sandstone, OK
  • Early Cretaceous – 110 mya

This skeleton of Acrocanthosaurus was excavated over a period of three years, beginning in 1983, from private land in McCurtain County in southeastern Oklahoma, by amateur collectors Cephis Hall and Sid Love. The specimen was eventually purchased by Allen and Fran Graffham of Geological Enterprises in Ardmore, Oklahoma, who also financed the initial preparation and restoration of thismagnificent skeleton. A team of expert fossil preparators at Black Hills Institute invested thousands of hours in the painstaking process of cleaning the bones, restoring the skeleton and creating a museum quality mount. Bob Farrar of Black Hills Institute noted that “Without the Graffham’s willingness to invest in the purchase and preparation of this specimen, scientists would still know very little about this intriguing but poorly understood dinosaur genus.”

The remains which had previously been found were so incomplete that scientists could not determine the lineage of Acrocanthosaurus, i.e. who were its relatives? Now, with this specimen prepared, a great deal more about Acrocanthosaurus and its family history have been discovered. As a result of the completeness of this specimen and its collection and preparation, scientists have been able to determine the close relationship of Acrocanthosaurus to Allosaurus, a Jurassic dinosaur from North America, and unite the mid Cretaceous African dinosaur, Carcharodontosaurus saharicus, to the Allosaurs as well.

The name Acrocanthosaurus atokensis was first assigned to two very incomplete skeletons excavated from Atoka County in Oklahoma which were described in 1950. Many trackways have been found with what have been described as the footprints of this apparently abundant, but extremely elusive, killer dinosaur. One well known trackway discovered near Glen Rose Texas shows what appears to be an attack upon a much larger sauropod (long necked) dinosaur by an Acrocanthosaurus.

Preparation of the specimen was notably more difficult than most due to the abundant pyrite (iron disulfide) growing out of and around the bones like moss on a rock.

When the pyrite was pulverized and removed, it released acids into the air requiring bones to be prepared in vacuum boxes or the use of respirators by preparators. In addition, the pyrite seemingly refused to part from the surface of the bone. This multiplied the number of hours needed for quality preparation as the pyrite had to be ‘rubbed’ off, often taking hours for one small patch.

The skeleton is marvelously preserved, the bones turned nearly jet black by minerals migrating via ground water through the sediment. This specimen also has nearly complete arms and shoulder girdles. The arms and shoulders of this Acrocanthosaurus are much larger and more heavily muscled and thus probably more powerful than the arms of Tyrannosaurus rex. Each arm terminates in three wickedly curved large claws, well designed for capturing and holding prey. There is evidence in the skeleton of what was probably a near fatal ‘hunting accident’ in a punctured shoulder blade and several broken ribs that have healed. “Obviously, even this powerful predator had enemies capable of causing it serious damage,” said Neal Larson when the injuries were uncovered during preparation.

One of the most bizarre and prominent identifying features of the Acrocanthosaurus species is the presence of extremely long spines along the top of the vertebrae of the back, hips and tail. These long spines give this dinosaur a surreal appearance even as a skeleton. They must have imparted a fiercely menacing, almost armored look, to the living predator. These spines also gave this dinosaur its name as Acrocanthosaurus, literally translated, means “high spined lizard”. Allen Graffham says; “Everyone who sees this magnificent skeleton will understand how and why it got its name”.

The skull is one of the most complete dinosaur skulls ever excavated. It was flattened during its time in the ground and the initial preparation included cleaning just the sides and perimeter, which was a considerable undertaking. In December of 1997, the original fossil skeleton was purchased by the Friends of the North Carolina State Museum of Natural Sciences (Raleigh, North Carolina). The skull was then completely cleaned apart and inflated, revealing the beautiful interior bones never before seen in any other Acrocanthosaurus specimen. Preparators at Black Hills Institute noted this preparation as among the most difficult they had done.

The original skeleton was mounted (sans the skull) in BHIGR’s modular style with the bones strapped or cradled to leave them accessible for future study. The mount and skull were delivered to the North Carolina museum in November of 1999 and are now on display in the new museum building in Raleigh, North Carolina.

Reproductions of this magnificent skeleton, the skull alone, the right arm, and several teeth are available from Black Hills Institute.