Acrocanthosaurus (/”AK-ro-KAN-tho-SAWR-us”/; “high-spined lizard”) is a genus of very large, meat-eating dinosaur. It belonged to a group called carcharodontosaurid theropods and lived during the Early Cretaceous period, approximately 113 to 110 million years ago. Fossils of Acrocanthosaurus have been discovered mainly in North America, in states like Oklahoma, Texas, and Wyoming. The name Acrocanthosaurus comes from the Greek words “akros” (high), “akantha” (spine or thorn), and “sauros” (lizard), referring to the unusually tall spines on many of its backbones, which formed a noticeable ridge.
Description and Classification
Acrocanthosaurus was a large predator that walked on two powerful hind legs. Scientists estimate that adult Acrocanthosaurus could grow to be about 11 to 11.5 meters (36 to 38 feet) long and weigh between 5.6 and 6.2 metric tons (6.2 to 6.8 short tons). This made it one of the biggest meat-eating dinosaurs of its time. Its skull was long and somewhat low, measuring about 1.3 meters (4.3 feet) in length. The skull had several large openings, called fenestrae, which helped to make it lighter without losing strength. It had powerful jaws filled with sharp, blade-like teeth suitable for slicing flesh. Its arms were relatively short but muscular, each ending in a hand with three sharp claws. The most famous feature of Acrocanthosaurus is the series of tall neural spines on its vertebrae, running from its neck down to its tail. These spines were tallest over its back and hips.
Acrocanthosaurus is part of the group Theropoda, which includes most carnivorous dinosaurs. It is classified within the superfamily Allosauroidea and the family Carcharodontosauridae. This family includes other giant predatory dinosaurs, such as Carcharodontosaurus from Africa and Giganotosaurus from South America. The study of Acrocanthosaurus helps scientists understand how these large meat-eaters were related and spread across the world during the Cretaceous period.
Distinguishing Features
Acrocanthosaurus can be recognized by several special features:
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Tall Neural Spines: Its most striking feature is the row of very tall spines extending from its vertebrae (backbones). These spines could be more than twice the height of the main part of the vertebrae they grew from. They likely supported a thick, muscular ridge along the dinosaur’s back, different from the thin, skin-covered sail seen on dinosaurs like Spinosaurus.
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Skull Shape: The skull was long and relatively low, giving it a somewhat rectangular shape when seen from the side. This is different from the deeper, more robust skulls of later large theropods like Tyrannosaurus rex.
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Forelimbs: Although its arms were short compared to its body size, they were strong and equipped with three functional, heavily clawed fingers on each hand, likely used for grasping prey.
Paleoenvironment and Diet
Acrocanthosaurus lived in what is now North America during a part of the Early Cretaceous period called the Aptian and early Albian stages. The environment at that time consisted of wide floodplains, river systems, and forests, with a generally warm and humid climate. Acrocanthosaurus shared its world with many other types of dinosaurs. These included giant long-necked sauropods like Sauroposeidon and Paluxysaurus, which were likely among its main prey. Plant-eating ornithopods, such as Tenontosaurus, were also common. Smaller meat-eating dinosaurs, like Deinonychus, also lived in these areas.
As the top predator in its ecosystem, Acrocanthosaurus hunted large herbivorous dinosaurs. Its large size, strong build, and sharp teeth made it well-suited for this role. Fossilized trackways found in Texas, thought to have been made by an Acrocanthosaurus, show a large theropod possibly following a sauropod. This provides a rare glimpse into its potential hunting behavior. Bite marks found on the bones of some plant-eating dinosaurs from the same time and place are also consistent with Acrocanthosaurus attacks.
Significance and Ongoing Research
The discovery of Acrocanthosaurus is important because it shows that very large theropod dinosaurs were present in North America long before the famous Tyrannosaurus rex appeared. Well-preserved skeletons, especially a specimen nicknamed “Fran” (NCSM 14345) found in Oklahoma, have given paleontologists a lot of detailed information about its anatomy. This has helped improve our understanding of the Carcharodontosauridae family of dinosaurs.
Ongoing research on Acrocanthosaurus focuses on several specific topics:
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Function of the Tall Spines: Scientists are still studying the exact purpose of the tall neural spines. Ideas include providing attachment points for powerful back and neck muscles, being used for display to attract mates or scare rivals, or possibly for storing fat.
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Hunting and Feeding Mechanics: Researchers are investigating how Acrocanthosaurus hunted, the force of its bite, and how its skull and teeth were used to kill and eat prey. This often involves using computer models to test skull strength and jaw movement.
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Brain and Senses: By studying casts of the inside of its skull (endocasts), scientists can learn about the size and shape of its brain. This helps them make educated guesses about its senses, such as its ability to smell or see.
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Growth Patterns: Examining the microscopic structure of Acrocanthosaurus bones (bone histology) can help determine how fast these dinosaurs grew and how long it took them to reach their full adult size.
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Evolutionary Relationships: Studies continue to refine the exact placement of Acrocanthosaurus within the Carcharodontosauridae family and how it relates to other large theropods found on different continents.