Name Meaning: High Spine Reptile
Geologic Era: Early Cretaceous
Location Discovered: Oklahoma (original specimens)
Size: 11.5 meters long (around 38 feet)
Estimated Range: Western North America, with possible teeth recovered in Maryland
Extinction Date: 110 million years ago
Acrocanthosaurus is probably the best understood of the carcharodontosaurs. The reason for this is that we have more skeletal material from this animal than any others of its group. Carcharodontosaurs dominated the early Cretaceous, and would more than likely have been the apex predators of their environments. Tyrannosaurs, which would dominate in the Northern hemisphere in the later Cretaceous, were still relatively small, and would probably not have posed serious competition to their larger rivals.
Acrocanthosaurus, like its relatives, was characterized by a long, tapered skull, as opposed to the more stout construction of tyrannosaurid skulls. While not as powerful in terms of bite force as tyrannosaurs, the longer jaw would have been able to inflict more slashing-type wounds, as opposed to crushing damage.
Acrocanthosaurus gained its name from it unusually tall neural spines on its vertebrae (see image below). While the animal was alive, these processes could have supported anything from a fin-like sail to a hump of fatty or muscular tissue. If they did support fat or muscle, then the size and thickness of the hump would have been an indication of the health of the animal. In this case, bigger would have been better. It also could have served as an energy storage for more lean times, enabling Acrocanthosaurus to survive periods when food was more scarce, such as during a drought.
Another interesting feature about Acrocanthosaurus is that it could not pronate or supinate its forarms (for a human, that would be turning the hand palm side up and palm side down, respectively). It could move the arms side to side, though. This meant that the arms could not really be used for grabbing prey from above or below, but could be used to grasp from the side. The structure of the hand supports this idea in that two of the fingers were permanently flexed.
Once Acrocanthosaurus got its claws into a prey item, any attempt to pull away would only have driven the claws deeper. For this reason, it is thought that Acrocanthosaurus led its attack with its mouth, then used the claws as an anchor. If the prey was not killed by the initial bite, then the claws could be used to restrain the prey until the jaws could be used again.
Acrocanthosaurus is probably the maker of the trackway found in Dinosaur Valley State Park in Texas. While no bones have been associated with the tracks, paleontologists are fairly confident of the identification. Acrocanthosaurus was the only large predator described from that region and time, and the tracks match the size and shape that would be expected of a large theropod. An interesting feature of the trackway is that it parallels another set of tracks made by a sauropod, or group of sauropods. It is possible that this Acrocanthosaurus was stalking the herbivores, but equally possible that the predator just happened to come along later and followed roughly the same path.
Skull By Christophe Hendrickx – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=24030326
Skeleton: By Sergey Galyonkin [CC BY-SA 2.0 (https://creativecommons.org/licenses/by-sa/2.0)], via Wikimedia Commons
Life Restoration: By Dmitry Bogdanov – email@example.com, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=3143319