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Dinosauromorpha

Dinosauromorpha

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Dinosauromorpha is the name of a clade
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...

s that includes the closest relatives of 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 the order Dinosauria itself. Basal forms include Saltopus
Saltopus
Saltopus is a genus of very small bipedal dinosauriform, roughly 60 centimeters long, not much bigger than a rabbit, that was discovered in Scotland by Friedrich von Huene in 1910. It was a late Triassic carnivore. Probably the size of a small cat, with hollow bones like those of a bird,...

, Marasuchus
Marasuchus
Marasuchus is a genus of dinosaur-like ornithodiran from the middle Triassic Chañares Formation of Argentina. The species Marasuchus lilloensis was originally described as a second species of Lagosuchus, L. lilloensis...

, the perhaps identical Lagosuchus
Lagosuchus
Lagosuchus is a genus of small archosaur from the middle Triassic period. It is generally thought to be closely related to dinosaurs, as a member of the Dinosauromorpha...

, the lagerpetonids
Lagerpetonidae
The Lagerpetonidae is a family of basal dinosauromorphs. Members of the family are known from the Late Triassic of Argentina, Arizona, New Mexico, and Texas.-Description:...

 Lagerpeton
Lagerpeton
Lagerpeton is a genus of basal dinosauromorph from the Ladinian . Lagerpeton is known from several specimens of hindlimbs, hips, vertebrae, and feet. It was about 0.7 metres long and was found in the Chañares Formation of Argentina. It has unique feet, with an unusually long fourth toe...

from the Ladinian
Ladinian
The Ladinian is a stage and age in the Middle Triassic series or epoch. It spans the time between 237 ± 2 Ma and 228 ± 2 Ma...

 of Argentina
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...

 and Dromomeron
Dromomeron
Dromomeron is a genus of lagerpetonid dinosauromorph archosaur from Late Triassic-age rocks of the Southwestern United States. It is known from partial remains, largely from the hindlimbs,, which indicate an animal with an overall length of less than 1.0 meters...

from the Norian
Norian
The Norian is a division of the Triassic geological period. It has the rank of an age or stage . The Norian lasted from 216.5 ± 2.0 to 203.6 ± 1.5 million years ago. It was preceded by the Carnian and succeeded by the Rhaetian.-Stratigraphic definitions:The Norian was named after the Noric Alps in...

 of Arizona
Arizona
Arizona ; is a state located in the southwestern region of the United States. It is also part of the western United States and the mountain west. The capital and largest city is Phoenix...

, New Mexico
New Mexico
New Mexico is a state located in the southwest and western regions of the United States. New Mexico is also usually considered one of the Mountain States. With a population density of 16 per square mile, New Mexico is the sixth-most sparsely inhabited U.S...

, and Texas
Texas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...

, and the silesaurids, which include Silesaurus
Silesaurus
Silesaurus is a genus of dinosauriform from the Late Triassic, approximately 230 million years ago in the Carnian faunal stage of what is now Poland....

from the Carnian
Carnian
The Carnian is the lowermost stage of the Upper Triassic series . It lasted from about 228.7 till 216.5 million years ago . The Carnian is preceded by the Ladinian and is followed by the Norian...

 of Poland
Poland
Poland , officially the Republic of Poland , is a country in Central Europe bordered by Germany to the west; the Czech Republic and Slovakia to the south; Ukraine, Belarus and Lithuania to the east; and the Baltic Sea and Kaliningrad Oblast, a Russian exclave, to the north...

, Eucoelophysis
Eucoelophysis
Eucoelophysis is a genus of dinosauriform from the Late Triassic period Chinle Formation of New Mexico...

from the Carnian-Norian of New Mexico, Lewisuchus
Lewisuchus
Lewisuchus is a genus of archosaur that lived during the Middle Triassic ; it was a silesaurid dinosauriform, a member of the group of reptiles which lead to the dinosaurs. Lewisuchus was about three feet long. Fossils have been found in Argentina...

and the perhaps identical Pseudolagosuchus
Pseudolagosuchus
Pseudolagosuchus is a genus of dinosauromorph from the Middle Triassic Chañares Formation of Argentina. It may be a junior synonym of Lewisuchus, but there is very little overlapping material...

from the Ladinian of Argentina, Sacisaurus
Sacisaurus
Sacisaurus is a dinosauriform from the Late Triassic Caturrita Formation of southern Brazil...

from the Norian of Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...

, Technosaurus
Technosaurus
Technosaurus is an extinct genus of Late Triassic archosauriform, perhaps a dinosauriform similar to Silesaurus, from the Norian age Upper Triassic Bull Canyon Formation of Texas...

from the Carnian of Texas, 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....

from 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...

 of Tanzania
Tanzania
The United Republic of Tanzania is a country in East Africa bordered by Kenya and Uganda to the north, Rwanda, Burundi, and the Democratic Republic of the Congo to the west, and Zambia, Malawi, and Mozambique to the south. The country's eastern borders lie on the Indian Ocean.Tanzania is a state...

, and Diodorus
Diodorus (genus)
Diodorus is a genus of silesaurid dinosauriform from the The Late Triassic Timezgadiouine Formation of the Argana Basin of Morocco...

from the Carnian(?) to Norian of Morocco
Morocco
Morocco , officially the Kingdom of Morocco , is a country located in North Africa. It has a population of more than 32 million and an area of 710,850 km², and also primarily administers the disputed region of the Western Sahara...

. Birds are the only surviving dinosauromorphs.

The name was coined by Michael J. Benton
Michael J. Benton
Michael J. Benton is a British paleontologist, a Fellow of the Royal Society of Edinburgh, and professor of vertebrate palaeontology in the Department of Earth Sciences at the University of Bristol....

 in 1984. The first clade definitions were by Paul Sereno
Paul Sereno
Paul Callistus Sereno is an American paleontologist from the University of Chicago who discovered several new dinosaur species on several continents. He has conducted excavations at sites as varied as Inner Mongolia, Argentina, Morocco, and Niger...

 in 1991 who accidentally defined the concept as both a node clade: the last common ancestor of Lagerpeton chanarensis, Lagosuchus talampayensis, Pseudolagosuchus major and the Dinosauria (including Aves) and all its descendants, and a stem clade: those Ornithodira more closely related to Dinosauria than to Pterosauria. A more specific definition was given by Sereno in 2005: the group consisting of Passer domesticus
House Sparrow
The House Sparrow is a bird of the sparrow family Passeridae, found in most parts of the world. One of about 25 species in the genus Passer, the House Sparrow occurs naturally in most of Europe, the Mediterranean region, and much of Asia...

(Linnaeus 1758) and all species closer to Passer than to Pterodactylus
Pterodactylus
Pterodactylus is a genus of pterosaurs, whose members are popularly known as pterodactyls. It was the first to be named and identified as a flying reptile...

 antiquus
(Soemmerring 1812), Ornithosuchus
Ornithosuchus
Ornithosuchus is an extinct genus of crurotarsan from the Late Triassic Lossiemouth Sandstone of Scotland...

 woodwardi
(Newton 1894) and Crocodylus niloticus
Nile crocodile
The Nile crocodile or Common crocodile is an African crocodile which is common in Somalia, Ethiopia, Uganda, Kenya, Egypt, Tanzania, Zambia, Zimbabwe, Gabon, South Africa, Malawi, Sudan, Botswana, and Cameroon...

(Laurenti 1768). Should the pterosaurs not be closely related to the dinosaurs, this new definition would still be relevant, defining also the relation to the Crurotarsi
Crurotarsi
The Crurotarsi are a group of archosauriformes, represented today by the crocodiles,...

; in that case it would be an older synonym of Avemetatarsalia
Avemetatarsalia
Avemetatarsalia is a clade name established by British palaeontologist Michael Benton in 1999 for all crown group archosaurs that are closer to birds than to crocodiles. It includes a similarly defined subgroup, Ornithodira...

.

Dinosauromorphs appeared by 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...

 stage of the Middle Triassic
Middle Triassic
In the geologic timescale, the Middle Triassic is the second of three epochs of the Triassic period or the middle of three series in which the Triassic system is divided. It spans the time between 245 ± 1.5 Ma and 228 ± 2 Ma...

 around 242 to 244 million years ago, splitting from other ornithodires. Early Triassic
Early Triassic
The Early Triassic is the first of three epochs of the Triassic period of the geologic timescale. It spans the time between 251 ± 0.4 Ma and 245 ± 1.5 Ma . Rocks from this epoch are collectively known as the Lower Triassic, which is a unit in chronostratigraphy...

 footprints reported in October 2010 from the Świętokrzyskie (Holy Cross) Mountains
Swietokrzyskie Mountains
Świętokrzyskie Mountains , are a mountain range in central Poland, in the vicinity of the city of Kielce. The mountain range consists of a number of separate ranges, the highest of which is Łysogóry . The two highest peaks are Łysica at 612 meters and Łysa Góra at 593 meters...

 of Poland may belong to a dinosauromorph. If so, the origin of dinosauromorphs would be pushed back into the Early Olenekian
Olenekian
In the geologic timescale, the Olenekian is an age in the Early Triassic epoch or a stage in the Lower Triassic series. It spans the time between 249.7 ± 0.7 Ma and 245 ± 0.7 Ma . The Olenekian follows the Induan and is followed by the Anisian.The Olenekian saw the deposition of a large part of the...

, around 249 Ma. The oldest Polish footprints are from a small quadrupedal animal named Prorotodactylus
Prorotodactylus
Prorotodactylus is an dinosauromorph ichnogenus known from fossilized footprints found in Poland and France. It may have been made by a dinosauromorph that was a precursor to the dinosaurs, possibly closely related to Lagerpeton. Fossils of Prorotodactylus date back to the early Olenekian stage of...

, but footprints belonging to the ichnogenus Sphingopus
Sphingopus
Sphingopus is an ichnogenus of dinosauriform footprints found in sediments dating to 250 and 228 Ma. The exact species which created Sphingopus tracks have not been identified.-Specimens:Sphingopus type footprints are known from two locations...

that have been found from Early Anisian strata show that moderately large bipedal dinosauromorphs had appeared by 246 Ma. The tracks show that the dinosaur lineage appeared soon after the Permian-Triassic extinction event
Permian-Triassic extinction event
The Permian–Triassic extinction event, informally known as the Great Dying, was an extinction event that occurred 252.28 Ma ago, forming the boundary between the Permian and Triassic geologic periods, as well as the Paleozoic and Mesozoic eras...

. Their age suggests that the rise of dinosaurs was slow and drawn out across much of the Triassic.

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