not equivalent to Pseudosuchia, which by definition must include all crocodilian-line archosaurs. For many years, Pseudosuchia and Crurotarsi have been considered partial synonyms because the latter clade encompasses all crocodilian-line archosaurs in most phylogenetic analyses. Sterling Nesbitt's 2011 analysis places one crurotarsan group, Phytosauria, outside Pseudosuchia. Since the definition of Crurotarsi relies on phytosaurs, their placement outside Pseudosuchia (and thus Archosauria) means that the clade Crurotarsi includes both pseudosuchians and avemetatarsalians. Description Pseudosuchia is one of the two primary "daughter" clades of the Archosauria. The skull is often massively built, especially in contrast to ornithodires; the snout is narrow and tends to be elongated, the neck is short and strong, and the limb posture ranges from a typical reptilian sprawl to an erect stance like dinosaurs' or mammals', although achieving it a different way. The body is often protected by two or more rows of armored plates. Many crurotarsans reached lengths of three meters or more. Evolution Pseudosuchians appeared during the late Olenekian (early Triassic); by the Ladinian (late Middle Triassic) they dominated the terrestrial carnivore niches. Their heyday was the Late Triassic, during which time their ranks included erect-limbed rauisuchians, herbivorous armored aetosaurs, the large predatory poposaurs, the small agile sphenosuchian crocodilians, and a few other assorted groups. The end-Triassic extinction caused the extinction of all the pseudosuchians with the exception of Sphenosuchia and Crocodyliformes (both Crocodylomorpha), the latter being the ancestors of modern-day crocodiles. A study published in 2010 postulates that there is significant evidence that volcanic eruptions changed the climate, causing a mass extinction that wiped out the dinosaurs' main competitors. This allowed the dinosaurs to succeed them as the dominant terrestrial carnivores and herbivores. As the Mesozoic progressed, the Protosuchia gave rise to more typically crocodile-like forms. While dinosaurs were the dominant animals on land, the crocodiles flourished in rivers, swamps, and the oceans, with far greater diversity than they have today. With the end-Cretaceous extinction, the dinosaurs became extinct, with the exception of the birds, while the crocodilians continued with little change. Today, the crocodiles, alligators, and gharials are the surviving representatives of this lineage. Interestingly, the Mesozoic range of cranial disparity is higher than the Triassic one, suggesting crocodylomorphs attained a high degree of diversification compared to Triassic pseudosuchians. Phylogeny Pseudosuchia was defined as a stem-based clade in 1985. It includes crocodiles and all archosaurs more closely related to crocodiles than to birds. A