Achelousaurus
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What is Achelousaurus?
Achelousaurus horneri was a herbivorous ceratopsian dinosaur that lived in Montana during the Late Cretaceous Period, between 83 million and 70 million years ago. The genus name references Achelous, a Greek river god who transformed into a bull and lost a horn in a fight with Hercules.
Achelousaurus belonged to the Centrosaurinae subfamily. Unlike the related Triceratops, it had bony knobs, called horn bosses, instead of horns above its eyes, and it lacked a large nasal horn.
Fossil analysis indicates that Achelousaurus grew to 6 meters (20 feet) long, possessing a parrot-like beak and teeth suited for eating plants. It had two horns extending from its frill, which may have served for defense, cooling, or attracting mates.
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When and where did Achelousaurus live?
Achelousaurus horneri, a herbivorous ceratopsian dinosaur, lived in Montana during the Late Cretaceous Period, specifically between 83 million and 70 million years ago. Fossils of Achelousaurus have been discovered in the Two Medicine Formation in northwestern Montana, a rock formation composed of nonmarine sediments.
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What did Achelousaurus look like?
The Achelousaurus was a herbivorous ceratopsian dinosaur that lived in Montana during the Late Cretaceous Period, roughly 83 million to 70 million years ago.
Achelousaurus was a centrosaurine. Unlike the chasmosaurines, centrosaurines had horn bosses (raised, bony knobs) rather than long postorbital horns on their faces near their eyes.
Fossil analyses suggest that Achelousaurus grew to a length of 6 meters (20 feet). It had a beak similar to that of a present-day parrot, and its teeth suggest that it ate plants. While the species had no horns on its face, it did have two horns extending from its frill, which may have served as a defense, a cooling mechanism, or a means to attract a mate.
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What kind of environment did Achelousaurus inhabit?
Achelousaurus lived in a swampy, subtropical environment in what is now northwestern Montana. This area was part of the Two Medicine Formation, made of nonmarine sediments deposited between 83 and 75 million years ago during the Late Cretaceous Epoch. During this time, the climate was generally warmer than today, with tropical to subtropical conditions extending as far as 45° N latitude. The region was a coastal plain with dense forests of palms and giant redwoods.
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How did Achelousaurus use its horns and frill?
Achelousaurus was a herbivorous ceratopsian that lived in Montana during the Late Cretaceous Period. Achelousaurus belonged to the centrosaurines, a subfamily of Ceratopsians. Unlike other ceratopsians, Achelousaurus did not have horns on its face; instead, it possessed two horns that extended from its frill.
The function of the horns and frill of Achelousaurus may have been for defense, cooling, or to attract a mate. Ceratopsians may have used their horns for defense against predators or in rutting combat with other males. The fact that both sexes had horns suggests that they were also used for species recognition.
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How do scientists study and learn about dinosaurs like Achelousaurus?
Scientists study dinosaurs like Achelousaurus using various methods. Paleontologists find Achelousaurus fossils in nonmarine sedimentary rock formations, such as the Two Medicine Formation in Montana.
To study Achelousaurus, paleontologists describe and analyze fossils and compare them to other known dinosaurs to develop hypotheses about evolutionary relationships. They analyze the fossils of the skull to estimate the size and diet of Achelousaurus. Functional anatomic studies use traits of present-day animals, along with mechanical and theoretical models, to visualize aspects of extinct animals. Isotopic dating and the study of radioactive decay help determine the age of fossils.
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Achelousaurus, (Achelousaurus horneri), herbivorous ceratopsian dinosaur that lived between 83 million and 70 million years ago during the Late Cretaceous Period (100.5 million to 66 million years ago) in Montana. The genus Achelousaurus is named for the ancient Greek shape-shifting river god, Achelous, who, according to myth, transformed himself into a bull while fighting Hercules, who broke off one of his Achelous’s horns during the contest. The three specimens of Achelousaurus are housed at the Museum of the Rockies in Bozeman, Montana.
Natural history
Ceratopsians are divided into two subfamilies: Chasmosaurinae and Centrosaurinae. While most ceratopsians, including Triceratops, had horns on their heads, the chasmosaurines, such as Triceratops, also had long bony crests, or frills, that grew from the base of the skull to cover the upper part of the dorsal side of the body, long horns above the eyes, and a short horn on the nose. Centrosaurines, which included Achelousaurus, had horn bosses (that is, raised, bony knobs) rather than long postorbital horns on their faces near their eyes. Some centrosaurines had large nasal horns as well; however, Achelousaurus did not.
Fossil analyses of the skull of Achelousaurus (which was 1.6 meters [5.2 feet] long) suggest that Achelousaurus grew to a length of 6 meters (20 feet). Like other ceratopsians, Achelousaurus had a beak similar to that of a present-day parrot, and the structure of its teeth suggests that it was a plant eater. While the species had no horns on its face, it possessed two horns that extended from its frill, which may have served as a defense or cooling mechanism or as a means to attract a mate.
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Fossil discoveries
Multiple centrosaurine fossils have been found in the Two Medicine Formation in northwestern Montana. This rock formation, which is composed of nonmarine sediments, was deposited between 83 and 75 million years ago (see also sedimentary rock). American paleontologist Jack Horner was responsible for leading the team of researchers that uncovered the first Achelousaurus skull, MOR 485, in 1987, with Sid Hofsteader credited with the skull’s discovery. The fossil lay in the uppermost 20 meters (65.6 feet) of the formation. The species was first described in 1995 by Canadian paleontologist Scott Sampson. Sampson named the single specimen, which was first known as “Taxon C,” as Achelousaurus horneri, for Horner. Along with this single cranium, two additional specimens of juvenile individuals (MOR 591 and MOR 571) were first described in 1989 and 1995, respectively.
Paleontologists also discovered two other species in different rock strata: Rubeosaurus ovatus, a sister taxon to Einiosaurus procurvicornis (initially called “Taxon B”). The first centrosaurine from this formation, known initially as “Taxon A,” was named Styracosaurus ovatus. These three species are thought to have descended from S. albertensis. Achelousaurus is likely related to Einiosaurus, which had a downward-facing curved horn on its nose and two horns on its frill. In addition, there is some evidence that Achelousaurus may be the direct ancestor to Pachyrhinosaurus, a centrosaurine whose skull was characterized by a narrow but massive beak and a bony frill.