Dinosauriformes
Encyclopedia
Dinosauriformes is a clade
of archosaur
ian reptile
s that include the dinosaur
s and their most immediate relatives. All dinosauriformes are distinguished by several features, such as shortened forelimbs, and an at least partially perforated acetabulum
, the hole in the hip socket traditionally used to define dinosaurs. The oldest known member is Asilisaurus
, dating to about 245 million years ago in the Anisian
age of the middle Triassic
period.
The term Dinosauriformes was coined and defined in 1992 by F.E. Novas, who used it to include the herrerasaurs, which he did not consider members of Dinosauria proper. Contrary to Novas, most paleontologists since 1992 have considered herrerasaurs to be true dinosaurs, though many other primitive, dinosaur-like reptiles fall within his definition of Dinosauriformes. Dinosauriformes fall within the clade Dinosauromorpha
.
simplified after Nesbitt (2011):
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
of archosaur
Archosaur
Archosaurs are a group of diapsid amniotes whose living representatives consist of modern birds and crocodilians. This group also includes all extinct non-avian dinosaurs, many extinct crocodilian relatives, and pterosaurs. Archosauria, the archosaur clade, is a crown group that includes the most...
ian reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
s that include the dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
s and their most immediate relatives. All dinosauriformes are distinguished by several features, such as shortened forelimbs, and an at least partially perforated acetabulum
Acetabulum
The acetabulum is a concave surface of the pelvis. The head of the femur meets with the pelvis at the acetabulum, forming the hip joint.-Structure:...
, the hole in the hip socket traditionally used to define dinosaurs. The oldest known member is Asilisaurus
Asilisaurus
Asilisaurus , and Greek, σαυρος is an extinct genus of silesaurid archosaur. It is the oldest avian-line archosaur, dating to about 245 million years ago....
, dating to about 245 million years ago in the Anisian
Anisian
In the geologic timescale, the Anisian is the lower stage or earliest age of the Middle Triassic series or epoch and lasted from 245 million years ago until 237 million years ago, approximately...
age of the middle Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
period.
The term Dinosauriformes was coined and defined in 1992 by F.E. Novas, who used it to include the herrerasaurs, which he did not consider members of Dinosauria proper. Contrary to Novas, most paleontologists since 1992 have considered herrerasaurs to be true dinosaurs, though many other primitive, dinosaur-like reptiles fall within his definition of Dinosauriformes. Dinosauriformes fall within the clade Dinosauromorpha
Dinosauromorpha
Dinosauromorpha is the name of a clade of archosaurs that includes the closest relatives of dinosaurs, and the order Dinosauria itself. Basal forms include Saltopus, Marasuchus, the perhaps identical Lagosuchus, the lagerpetonids Lagerpeton from the Ladinian of Argentina and Dromomeron from the...
.
Phylogeny
CladogramCladogram
A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...
simplified after Nesbitt (2011):