Dinosauromorpha is the name of a clade of archosaurs that includes the closest relatives of dinosaurs, and the order Dinosauria itself. Basal forms include Marasuchus, the perhaps identical Lagosuchus, the lagerpetonids Lagerpeton from the Ladinian of Argentina and Dromomeron from the Norian of Arizona, New Mexico, and Texas, and "silesaurs", which include Silesaurus from the Carnian of Poland, Eucoelophysis from the Carnian-Norian of New Mexico, Pseudolagosuchus from the Ladinian of Argentina, and potentially Sacisaurus from the Norian of Brazil, and Technosaurus from the Carnian of Texas. Birds are the only surviving dinosauromorphs.
The name was coined by Michael J. Benton in 1984. The first clade definitions were by Paul Sereno 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 (Linnaeus 1758) and all species closer to Passer than to Pterodactylus antiquus (Soemmerring 1812), Ornithosuchus woodwardi (Newton 1894) and Crocodylus niloticus (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; in that case it would be an older synonym of Avemetatarsalia.
Dinosauromorphs appeared by the Anisian stage of the Middle Triassic around 242 to 244 million years ago, splitting from other ornithodires. Early Triassic footprints reported in October 2010 from the Świętokrzyskie (Holy Cross) Mountains of Poland may belong to a dinosauromorph. If so, the origin of dinosauromorphs would be pushed back into the Early Olenekian, around 249 Ma. The oldest Polish footprints are from a small quadrupedal animal named Prorotodactylus, but footprints belonging to the ichnogenus Sphingopus 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. Their age suggests that the rise of dinosaurs was slow and drawn out across much of the Triassic.
1. ^ Irmis, Randall B.; Nesbitt, Sterling J.; Padian, Kevin; Smith, Nathan D.; Turner, Alan H.; Woody, Daniel; and Downs, Alex (2007). "A Late Triassic dinosauromorph assemblage from New Mexico and the rise of dinosaurs". Science 317 (5836): 358–361. doi:10.1126/science.1143325. PMID 17641198.
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