Scientific Classification
Kingdom: Animalia
Phylum: Chordata
Order: Therapsida
Suborder: Paracrocodylomorpha
Family: Ctenosauriscidae
Genus: Arizonasaurus

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The Arizonasaurus is so named after the place of its discovery, Arizona. It is a proposaurid Archosaur. It lived in the Middle Triassic Period in the region of present day North America. The creature is more than 243 million years old. It displays a characteristic sail on its back like some Archosaurs. It was a flesh eating creature.

The discovery of fossils
The fossils of the Arizonasaurus, as the name suggest were found in Northern Arizona's middle Triassic Moenkopi Formation by Samuel Paul Welles in 1947. The skeletal remains contained some teeth and a jawbone. Welles named the specimen, Arizonasaurus babbitti. The holotype was labelled specimen UCMP 36232. Another complete skeleton was found by Sterling Nesbitt in 2002. Both the specimens are now housed at the Museum of Paleontology of the University of California.

The Middle Triassic
The Middle Triassic is the intermediate epoch amongst all the three epochs of the Triassic period. It is preceded by the Early Triassic and followed by the Late Triassic. It stretches from 247.2 million years ago to 235 million years ago. The Middle Triassic was divided into two stages: the Anisian and the Ladinian.
The Arizonasaurus belonged to the Anisian stage of the middle Triassic period. The Anisian is the earlier of the two stages of the Middle Triassic. It spans the time interval from 242 to 247.2 million years ago. Small dinosaurs had began to appear in this period. The Anisian period was followed by the Ladinian stage of the middle Triassic and preceded by the Olenekian of the early Triassic period.

The Moenkopi formation and the discoverers
The Moenkopi is a geological landform that stretches across New Mexico, Arizona, Nevada, California, eastern Utah, and Western Colorado of the United States. The Moenkopi foundation is rich in skeletal remains, particularly in two members - the Wupatki and the Holbrook from Northern Arizona. It is a part of the Colorado Plateau, Basin and Range and includes parts of the Lower as well as the middle Triassic.
A great many basal vertebrate fossils and specimens have been discovered and isolated from the Moenkopi foundation. This region is important from a geological point of view as there is rare data from the Middle and Lower Triassic period elsewhere. Other specimens and footprints found in the Moenkopi foundation include lungfish, Wellesaurus, Rhynchosaur Ammorhynchus and Anisodontosaurus besides the Arizonasaurus.
Samuel P. Welles, an American paleontologist and research associate at the UCMP, Berkeley was born on the 9th of November, 1909 in Massachusetts. Besides discovering the Arizonasaurus, he was a part of the Placerias Quarry excavations, 1930 and also the Shonisaurus discoveries in 1954. He is most renowned for describing the Dilophosaurus in the year 1954.
Sterling Nesbitt, the American paleontologist was born on March 25th, 1982 in Mesa, Arizona. He is widely recognized for his work on the discovery and isolation of Triassic Archosaurs.

Physical Features and Anatomical details
The Arizonasaurus resembles other known basal archosaurs like the Ctenosauriscus and the Lotosaurus. Along with a few other archosaurs, they make up the Ctenosauriscidae. These creatures are closely related to the proposaurids. The pelvic girdle of the Arizonasaurus is key to classifying the taxon with the likes of Ctenosauriscus and Bromsgroveia.
The Arizonasaurus had tall neural spines on its dorsal vertebrae. The function of this particular anatomical feature is still unknown. These neural spines could have supported either a hump or a sail on the creatures back. The study of the Arizonasaurus dinosaur's braincase has revealed that the dinosaurs possess some ancestral features for Crurotarsans.
Analysis of the two known specimens of the species by Nesbitt in 2005 revealed two automorphies that helped distinguish the Arizonasaurus. These two features are:
A deep, obscured-from-view cavity in the poster ventral edge of the upward pointing face of the jawbone
A tongue-groove tendon attaching the pubic bone to the illium.

The Arizonasaurus was estimated to be around 3 meters long. The height of the Arizonasaurus was a bit less than a meter or roughly, half the size of an average human being. The estimated weight of the Arizonasaurus is roughly 500 pounds.

Recent Studies
A phylogenetic study on the Arizonasaurus classifies it with the Yarasuchus and the Qianosuchus, both ticinosuchians without a sail or hump on their dorsal vertebrae.

About the Arizonasaurus
The Arizonasaurus was quadrapedal i.e. walked on four legs. Despite this, scientists think it is a good candidate for plausible bipedalism, since it incorporates features that could help it to stand on its hind legs. This is due to a gracile pectoral girdle and the sail that could also serve the purpose of strength to the backbone. One function of the sail on the Arizonasaurus' back would be thermoregulation. The sail could help to increase or decrease air turbulence. The neural spines could also support a hump for storing fat. It could also be for the purpose of display, like antlers serve for stags.
It was a carnivorous creature and a natural predator. It had a long, heavy tail and a scaly exoskeleton. The tail provided perfect counterbalance. It had a deep pelvic girdle.
The study of archosaurs has gained more popularity after the 2002 fossils were unearthed. The data on archosaurs is limited, since a majority of the focus is on dinosaurs. However, the Archosaurs like the A. babbitti deserve more attention as they could provide vital about the early stages of the Triassic period, when dinosaurs were not into existence.
Archosaurs provide the perfect opportunity to study the merger of birds and reptiles as they incorporate features of both.  One crucial bit of information has already been deduced: that the deviation of birds and reptiles occurred earlier than paleontologists believed. Such information and more can be of importance in the study of prehistoric creatures.
Due to a sparked interest, more and more paleontologists are trying to analyze the Arizonasaurus and its sister taxa, with the hope of acquiring a breakthrough in Archosaur study. Such interest is certainly going to prove crucial if we want to learn more about the Pre-Jurassic geology and ecology of the Earth.