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Herrerasaur

 
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Herrerasaur
 
 
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Herrerasaurs are among the oldest known dinosaur
Dinosaur

Dinosaurs were the dominant vertebrate animals of Landform ecosystems for over 160 million years, from the late Triassic Period until the end of the Cretaceous Period , when most of them became extinct in the Cretaceous?Tertiary extinction event....
s, appearing in the fossil
Fossil

Fossils are the preserved remains or trace fossil of animals, plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous Rock formations and sedimentary rock layers is known as the fossil record....
 record about 228 million years ago (mid-Triassic
Triassic

The Triassic is a geologic period that extends from about 251 to 199 annum . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic....
). They became extinct by the end of the Triassic period. Herrerasaurs were small to medium-sized carnivore
Carnivore

A carnivore , meaning 'meat eater' , is any animal with a diet consisting mainly of meat, whether it comes from animals living or dead .In a more general sense, an animal may be considered a carnivore if it prefers feeding on animal matter over plant matter....
s generally resembling theropods, which may be their closest relatives. The best known representatives of this group are from South America
South America

South America is the southern continent of the Americas, situated entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere....
 (Brazil
Brazil

Brazil , officially the Federative Republic of Brazil , is a country in South America. It is the List of countries and outlying territories by total area country by geographical area, occupying nearly half of South America, the List of countries by population country, and the fourth most populous democracy in the world....
, Argentina
Argentina

Argentina, officially the Argentine Republic , is a country in South America, constituted as a federation of 23 provinces and an autonomous city....
), where they were first discovered in the 1960s. A nearly complete skeleton of Herrerasaurus ischigulastensis was discovered in the Ischigualasto
Ischigualasto

Ischigualasto is a geological formation and a natural park associated with it in the provinces of Argentina of San Juan Province, north-western Argentina, near the border with Chile....
 Formation in San Juan, Argentina, in 1988.






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Herrerasaurs are among the oldest known dinosaur
Dinosaur

Dinosaurs were the dominant vertebrate animals of Landform ecosystems for over 160 million years, from the late Triassic Period until the end of the Cretaceous Period , when most of them became extinct in the Cretaceous?Tertiary extinction event....
s, appearing in the fossil
Fossil

Fossils are the preserved remains or trace fossil of animals, plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous Rock formations and sedimentary rock layers is known as the fossil record....
 record about 228 million years ago (mid-Triassic
Triassic

The Triassic is a geologic period that extends from about 251 to 199 annum . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic....
). They became extinct by the end of the Triassic period. Herrerasaurs were small to medium-sized carnivore
Carnivore

A carnivore , meaning 'meat eater' , is any animal with a diet consisting mainly of meat, whether it comes from animals living or dead .In a more general sense, an animal may be considered a carnivore if it prefers feeding on animal matter over plant matter....
s generally resembling theropods, which may be their closest relatives. The best known representatives of this group are from South America
South America

South America is the southern continent of the Americas, situated entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere....
 (Brazil
Brazil

Brazil , officially the Federative Republic of Brazil , is a country in South America. It is the List of countries and outlying territories by total area country by geographical area, occupying nearly half of South America, the List of countries by population country, and the fourth most populous democracy in the world....
, Argentina
Argentina

Argentina, officially the Argentine Republic , is a country in South America, constituted as a federation of 23 provinces and an autonomous city....
), where they were first discovered in the 1960s. A nearly complete skeleton of Herrerasaurus ischigulastensis was discovered in the Ischigualasto
Ischigualasto

Ischigualasto is a geological formation and a natural park associated with it in the provinces of Argentina of San Juan Province, north-western Argentina, near the border with Chile....
 Formation in San Juan, Argentina, in 1988. Less complete herrerasaurians have been found in North America, and they may have inhabited other continents as well.

Herrerasaurian anatomy is unusual and specialized, and they are not considered to be ancestral to any later dinosaur group. They often present a mixture of very primitive and derived traits. The acetabulum
Acetabulum

The acetabulum is a :wikt:concave surface of the pelvis. The femur head meets with the pelvis at the acetabulum, forming the hip joint....
 is only partly open, and there are only two sacral vertebrae, the lowest number among dinosaurs. The pubic bone has a derived structure, being rotated somewhat posteriorly and folded to create a superficially tetanuran-like terminal expansion, especially prominent in H. ischigulastensis. The hand is primitive in having five metacarpals and the third finger longer than the second, but theropod-like in having only three long fingers, with curved claws. Herrerasaurids also have a hinged mandible
Mandible

The mandible or inferior maxillary bone forms the lower jaw and holds the lower tooth in place. It also refers to both the upper and lower sections of the beaks of birds....
 like theropods, but this may have evolved independently.

Taxonomy

  • Order Saurischia
    Saurischia

    Saurischia is one of the two Order s, or basic divisions, of dinosaurs. In 1888, Harry Seeley classified dinosaurs into two orders, based on their hip structure....
    • ?Suborder Theropoda
      Theropoda

      Theropods are a group of bipedal saurischian dinosaurs. Although they were primarily carnivorous, a number of theropod families evolved herbivore during the Cretaceous Period ....
      • Infraorder Herrerasauria
        • Family Staurikosauridae
          • Staurikosaurus
            Staurikosaurus

            Staurikosaurus is a genus of early dinosaur from the Late Triassic of Brazil....
        • Family Herrerasauridae
          • ?Caseosaurus
            Caseosaurus

            Caseosaurus is a genus of dinosaur from the Late Triassic of North America. It is named after E.C. Case. The type species, Caseosaurus crosbyensis, was formally described by Hunt, Lucas, Heckert, Sullivan and Lockley in 1998....
          • Chindesaurus
            Chindesaurus

            Chindesaurus is a genus of theropod dinosaur named after the Chinde Point, near where the genoholotype specimen was discovered in Petrified Forest National Park, Arizona, by Bryan Small in 1984....
          • Herrerasaurus
            Herrerasaurus

            Herrerasaurus was one of the earliest dinosaurs. All known specimens of this carnivore have been discovered in northwest of Argentina, in late Triassic Period rocks ....