Acrocanthosaurus, a large predator, dominated Early Cretaceous North America. Named for its “high-spined lizard” characteristic, this theropod had tall neural spines along its back. Measuring up to 11.5 meters (38 feet) long and weighing 4.4 to 8.4 metric tons, it was among the largest carnivores. Its fossil record helps paleontologists reconstruct the ancient world of Acrocanthosaurus atokensis in the United States.
Acrocanthosaurus’s Ancient Home
Acrocanthosaurus lived 113 to 110 million years ago during the Early Cretaceous. Fossils are found across North America, including Oklahoma, Texas, Wyoming, and Maryland. This period had a warm climate and rising sea levels, creating diverse environments.
The landscape featured floodplains, river deltas, and coastal shorelines. Formations like the Antlers (Oklahoma, Texas) and Arundel (Maryland) preserve this habitat. The Antlers Formation was a large floodplain, while Arundel was a freshwater fluvial environment. Vegetation included conifers, ferns, horsetails, and flowering plants.
Giants That Shared the Land
Acrocanthosaurus shared its environment with large dinosaurs, including potential prey. Prominent among these were sauropods, massive long-necked herbivores. Sauroposeidon proteles, a towering sauropod up to 18 meters (59 feet) tall and weighing 40 to 60 tons, coexisted with Acrocanthosaurus in Oklahoma, Wyoming, and Texas.
Another large sauropod in these formations was Astrodon, a Brachiosaurus relative. Smaller than Sauroposeidon, Astrodon was a significant food source. Large ornithopods like Tenontosaurus were also common herbivores. These multi-ton, bipedal dinosaurs were a primary prey item for Acrocanthosaurus.
Other predatory dinosaurs were present, though none matched Acrocanthosaurus in size or dominance. Deinonychus, a swift dromaeosaur, lived alongside Acrocanthosaurus. Measuring around 3 meters (10 feet) long, Deinonychus was smaller and likely hunted different prey, minimizing direct competition.
Smaller Dinosaurs and Other Reptiles
Beyond large dinosaurs, smaller creatures inhabited Acrocanthosaurus’s world. Armored dinosaurs like the nodosaurid Sauropelta were present in formations such as Cloverly. Sauropelta, a quadrupedal herbivore about 5.2 meters (17 feet) long, had bony plates and prominent shoulder spikes for defense against predators like Acrocanthosaurus.
The ecosystem also supported non-dinosaurian reptiles. Large crocodilians like Sarcosuchus prowled waterways. Turtles and lizards were present, with remains found in the Antlers and Arundel formations. Pterosaurs, flying reptiles, soared overhead. This diverse fauna indicates a complex food web.
How Paleontologists Piece Together the Past
Paleontologists reconstruct ancient ecosystems by analyzing fossil discoveries within geological contexts. Stratigraphy, the study of rock layers, is fundamental to this process.
By examining the order of sedimentary layers, scientists determine the relative ages of fossils, with older layers typically beneath younger ones. This allows correlation of species found in the same rock units, indicating coexistence.
For precise ages, paleontologists use radiometric dating, measuring radioactive isotope decay in igneous rocks or volcanic ash. Datable layers above and below fossil-bearing rocks provide a temporal bracket. While carbon-14 dates younger remains, potassium-argon dates rocks millions of years old.
Trace fossils offer insights into ancient animal behaviors and interactions. The Paluxy River trackways in Texas are a prime example, showing large three-toed theropod prints alongside sauropod trackways. These tracks, believed to belong to Acrocanthosaurus and Sauroposeidon, suggest the carnivore may have stalked its prey. Such fossilized behaviors provide direct evidence of Early Cretaceous relationships.