- Herrerasaur
Taxobox
name = Herrerasaurs
fossil_range =Late Triassic
image_width = 200px
image_caption = "Herrerasaurus "
regnum =Animal ia
phylum = Chordata
classis = Sauropsida
superordo =Dinosaur ia
ordo =Saurischia
subordo = ?Theropod a
infraordo = Herrerasauria
infraordo_authority = Galton, 1985
subdivision_ranks = Genera
subdivision =
* "Staurikosaurus "
* "Herrerasaurus "
* "Chindesaurus "
* ?"Caseosaurus "Herrerasaurs are among the oldest known
dinosaur s, appearing in thefossil record about 228 million years ago (mid-Triassic ). They became extinct by the end of the Triassic period. Herrerasaurs were small to medium-sizedcarnivore s generally resemblingtheropod s, which may be their closest relatives. The best known representatives of this group are fromSouth America (Brazil ,Argentina ), where they were first discovered in the 1960s. A nearly complete skeleton of "Herrerasaurus ischigulastensis" was discovered in theIschigualasto Formation in San Juan, Argentina, in1988 . 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 is only partly open, and there are only twosacral vertebrae , the lowest number among dinosaurs. Thepubic bone has a derived structure, being rotated somewhat posteriorly and folded to create a superficiallytetanuran -like terminal expansion, especially prominent in "H. ischigulastensis". The hand is primitive in having fivemetacarpal s and the third finger longer than the second, but theropod-like in having only three long fingers, with curved claws. Herrerasaurids also have a hingedmandible like theropods, but this may have evolved independently.Taxonomy
*Order
Saurischia
**?SuborderTheropoda
***Infraorder Herrerasauria
****Family Staurikosauridae
*****"Staurikosaurus "
****Family Herrerasauridae
*****?"Caseosaurus "
*****"Chindesaurus "
*****"Herrerasaurus "
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