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The Dinosaur Portal

Introduction

Herrerasaurus ischigualastensis
(a carnivorous basal dinosaur)

Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is a subject of active research. They became the dominant terrestrial vertebrates after the Triassic–Jurassic extinction event 201.3 mya and their dominance continued throughout the Jurassic and Cretaceous periods. The fossil record shows that birds are feathered dinosaurs, having evolved from earlier theropods during the Late Jurassic epoch, and are the only dinosaur lineage known to have survived the Cretaceous–Paleogene extinction event approximately 66 mya. Dinosaurs can therefore be divided into avian dinosaurs—birds—and the extinct non-avian dinosaurs, which are all dinosaurs other than birds.

Dinosaurs are varied from taxonomic, morphological and ecological standpoints. Birds, at over 11,000 living species, are among the most diverse groups of vertebrates. Using fossil evidence, paleontologists have identified over 900 distinct genera and more than 1,000 different species of non-avian dinosaurs. Dinosaurs are represented on every continent by both extant species (birds) and fossil remains. Through the first half of the 20th century, before birds were recognized as dinosaurs, most of the scientific community believed dinosaurs to have been sluggish and cold-blooded. Most research conducted since the 1970s, however, has indicated that dinosaurs were active animals with elevated metabolisms and numerous adaptations for social interaction. Some were herbivorous, others carnivorous. Evidence suggests that all dinosaurs were egg-laying, and that nest-building was a trait shared by many dinosaurs, both avian and non-avian. (Full article...)

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Acrocanthosaurus (meaning 'high-spined lizard') was a genus of allosauroid theropod dinosaur that existed in what is now North America during the mid-Cretaceous Period, approximately 125 to 100 million years ago. Like most dinosaur genera, Acrocanthosaurus contains only a single species, A. atokensis. Its fossil remains are found mainly in the U.S. states of Oklahoma and Texas, although teeth attributed to Acrocanthosaurus have been found as far east as Maryland.

Acrocanthosaurus was a bipedal predator. As the name suggests, it is best known for the high neural spines on many of its vertebrae, which most likely supported a ridge of muscle over the animal's neck, back and hips. Acrocanthosaurus was one of the largest theropods, approaching 12 meters (40 ft) in length, and weighing up to about 2.40 metric tons (2.65 short tons). Large theropod footprints discovered in Texas may have been made by Acrocanthosaurus, although there is no direct association with skeletal remains.

Recent discoveries have elucidated many details of its anatomy, allowing for specialized studies focusing on its brain structure and forelimb function. However, there is still debate over its evolutionary relationships, with some scientists classifying it as an allosaurid, and others as a carcharodontosaurid. Acrocanthosaurus was the largest theropod in its ecosystem and likely an apex predator which possibly preyed on large sauropods and ornithopods. (see more...)

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Dromaeosaurus skull mounted at the Muséum national d'Histoire naturelle in Paris.

Photo credit: User:LadyofHats

Did you know...

...that up to ten species of Psittacosaurus are recognized by scientists today, by far the most of any dinosaur genus?
...that Therizinosaurus, meaning "scythe lizard", is named after its hand claws, which could reach up to a meter in length?