Acrocanthosaurus atokensis

Acrocanthosaurus atokensis was a large theropod dinosaur that lived during the Early Cretaceous period, approximately 113 to 110 million years ago (Aptian–Albian). It was discovered in the Antlers Formation of Oklahoma, USA, with additional material found in Texas, Arkansas, and possibly Maryland.

The genus name Acrocanthosaurus means “high-spined lizard”, referring to the tall neural spines along its back, which formed a distinctive ridge. The species name atokensis comes from Atoka County, Oklahoma, where the holotype was found​.

This theropod was one of the top predators of its time, likely preying on large herbivorous dinosaurs such as sauropods and ornithopods.

Physical Characteristics

Acrocanthosaurus atokensis was a large carcharodontosaurid theropod, with an estimated length of 11.5 meters (37.7 ft) and a weight of up to 6,200 kg (13,670 lbs), based on NCSM 14345 and OMNH 10168.

Key anatomical features include:

• Tall neural spines on the vertebrae, over 2.5 times the height of the corresponding centra, forming a ridge along the back.
• Large skull, measuring approximately 1.3 meters (4.3 ft) in length, with a strong, deep structure.
• Massive forelimbs, relatively large for a carcharodontosaurid, with well-developed claws.
• Robust hindlimbs, supporting a powerful, bipedal stance.
• Long, muscular tail, likely aiding in balance and maneuverability​.

The function of the elongated neural spines is still debated. They may have supported a ridge of muscle or a sail-like structure, potentially aiding in thermoregulation, display, or energy storage.

Diet and Feeding Habits

As a large apex predator, Acrocanthosaurus likely hunted large herbivores such as sauropods (e.g., Pleurocoelus) and ornithopods (e.g., Tenontosaurus).

Key adaptations for hunting included:

• Large, serrated teeth, ideal for slicing through flesh.
• Powerful forelimbs with large claws, possibly used to hold onto struggling prey.
• Strong bite force, though less than that of Tyrannosaurus rex.
• Well-developed sense of smell and vision, aiding in tracking prey.

Fossilized trackways suggest that Acrocanthosaurus may have hunted in pairs or small groups, although this remains speculative​.

Habitat and Distribution

Acrocanthosaurus atokensis lived in what is now the south-central United States, with fossils found in Oklahoma, Texas, and Arkansas. The Antlers Formation and equivalent strata represent a coastal plain environment with a mixture of:

• Floodplains and river channels, providing ample prey.
• Open woodlands, where large dinosaurs roamed.
• Warm, semi-humid climate, similar to modern subtropical regions​.

Behavior and Social Structure

While direct evidence of Acrocanthosaurus behavior is limited, some inferences can be made:

• Likely a solitary or small-group hunter, similar to modern large predators.
• May have used ambush tactics, relying on powerful limbs and strong jaws.
• Possible territorial behavior, as seen in other large theropods​.

Discovery and Research

The first fossils of Acrocanthosaurus atokensis were described in 1950 by J. Willis Stovall and Wann Langston Jr., based on material from Atoka County, Oklahoma.

Key specimens include:

• Holotype (OMNH 10146) – Partial skeleton, including skull fragments.
• Paratype (OMNH 10147) – Additional skeletal elements.
• SMU 74646 – A more complete specimen found in Texas, including about 70% of the skeleton.
• NCSM 14345 – The most complete specimen, including a nearly complete skull and most of the postcranial skeleton, currently housed at the North Carolina Museum of Natural Sciences​.

Early classifications placed Acrocanthosaurus in Allosauridae, but later research confirmed its placement within Carcharodontosauridae, closely related to Giganotosaurus and Carcharodontosaurus.

Significance and Interesting Facts

• One of the largest theropods of the Early Cretaceous, reaching lengths comparable to Tyrannosaurus rex.
• Tall neural spines set it apart from most other large theropods.
• Forelimbs were more developed than those of later carcharodontosaurids, suggesting an important role in hunting.
• Trackways suggest it coexisted with giant herbivores like sauropods, providing a glimpse into Early Cretaceous predator-prey dynamics.
• Not a direct ancestor of Tyrannosaurus but shared the same ecosystem, predating the rise of large tyrannosaurs in North America​.