Arizonasaurus
Middle Triassic archosaur with a distinctive back sail.
Arizonasaurus, meaning "Arizona reptile," is a genus of ctenosauriscid archosaur that lived during the Middle Triassic, approximately 243 million years ago, in what is now Arizona. Its fossils were discovered in the Moenkopi Formation. The animal is most notable for a large sail along its back, formed by greatly elongated neural spines extending from its vertebrae. This sail resembled those of other early archosaurs, including related ctenosauriscids such as Ctenosauriscus, Bromsgroveia, and Hypselorhachis.
The type and only known species, *Arizonasaurus babbitti*, was named and described in 1947 by Samuel Paul Welles, based on a few teeth and a maxilla (specimen UCMP 36232). A much more complete skeleton, about fifty percent of the animal, was later discovered in 2002 by Sterling Nesbitt. Two braincase specimens have also been described, which retain some ancestral features that are plesiomorphic for crurotarsans. Distinctive characteristics identified by Nesbitt in 2005 include a deep, hidden fossa on the posteroventral edge of the upward-pointing process of the maxilla, and a tongue-groove attachment between the pubis and the ilium.
Classification places *Arizonasaurus* as a close relative of *Ctenosauriscus*, and together with several other genera they form the family Ctenosauriscidae. These ctenosauriscids share derived characteristics with the poposaurids. Features of the pelvic girdle link *Arizonasaurus* with *Ctenosauriscus*, *Lotosaurus*, *Bromsgroveia*, and *Hypselorhachis*. Newly identified pseudosuchian traits support the idea that other poposauroids, such as *Poposaurus*, *Sillosuchus*, and *Shuvosaurus*, along with ctenosauriscids, form a monophyletic group more derived than rauisuchians. The presence of a poposauroid in the early Middle Triassic suggests that the divergence of birds and crocodiles occurred earlier than previously thought. Ctenosauriscids from this time also indicate that Triassic faunas were more widespread across Europe, Asia, North America, and Africa. The fauna of the Moenkopi Formation represents a transitional stage between older and younger faunas.
- location
- Moenkopi Formation, northern Arizona
- classification
- Ctenosauriscid archosaur (pseudosuchian)
- type_species
- Arizonasaurus babbitti
- known_for
- Large back sail formed by elongated neural spines
Quick Facts
- Taxon
- Arizonasaurus
- Subdivision
- A. babbitti / Welles, 1947 (type)
Facts from the source article.
Lore & Background
Arizonasaurus is distinguished by a prominent sail along its back, formed by greatly elongated neural spines of the vertebrae, a feature it shares with other basal archosaurs such as *Ctenosauriscus*, *Bromsgroveia*, and *Hypselorhachis*. The genus is known from two braincase specimens, which retain several ancestral characteristics considered plesiomorphic for crurotarsans. The type and only species, *Arizonasaurus babbitti*, was originally named in 1947 based on a few teeth and a maxilla. A much more complete skeleton, representing about half of the animal, was discovered in 2002. Key anatomical traits that distinguish *Arizonasaurus* include a deep, hidden fossa on the posteroventral edge of the upward-pointing process of the maxilla, and a tongue-groove attachment between the pubis and ilium. The pelvic girdle of this archosaur unites it with *Ctenosauriscus*, *Lotosaurus*, *Bromsgroveia*, and *Hypselorhachis* within the group Ctenosauriscidae. These ctenosauriscids share derived characteristics with poposaurids, and together with poposauroids such as *Poposaurus*, *Sillosuchus*, and *Shuvosaurus*, they form a monophyletic group more derived than rauisuchians. *Arizonasaurus* lived during the Middle Triassic, approximately 243 million years ago, in what is now northern Arizona, within the Moenkopi Formation. Its presence in the early Middle Triassic suggests that the evolutionary divergence of birds and crocodiles occurred earlier than previously thought.
Reader's Guide
Arizonasaurus is significant as a well-preserved Middle Triassic pseudosuchian archosaur that helps clarify the early evolution of archosaurs, including the divergence of birds and crocodiles. Its presence in the Moenkopi Formation suggests that this divergence occurred earlier than previously thought. The ctenosauriscids, including Arizonasaurus, show that Triassic faunas were more widespread across Europe, Asia, North America, and Africa. The pelvic girdle of Arizonasaurus links it with Ctenosauriscus, Lotosaurus, Bromsgroveia, and Hypselorhachis, and newly identified pseudosuchian features indicate that poposauroids and ctenosauriscids form a monophyletic group more derived than rauisuchians. The fauna of the Moenkopi Formation represents a transitional stage between older and younger faunas.
Did You Know?
- Arizonasaurus means 'Arizona reptile'.
- Arizonasaurus had a sail made of tall neural spines, similar to those of Ctenosauriscus, Bromsgroveia, and Hypselorhachis.
Frequently Asked Questions
What is Arizonasaurus?
Arizonasaurus is a Middle Triassic archosaur whose type species is Arizonasaurus babbitti. It belongs to the ctenosauriscid family within the broader pseudosuchian lineage.
What is Arizonasaurus most famous for?
Its standout feature is a tall dorsal sail constructed from greatly elongated neural spines running along the vertebral column. This sail is the single trait that most sets it apart from other archosaurs of its era.
Where were Arizonasaurus fossils found?
Remains of this animal come from the Moenkopi Formation in northern Arizona. That rock unit preserves a Middle Triassic landscape in what is now the southwestern United States.
How is Arizonasaurus classified among prehistoric animals?
It is placed in the ctenosauriscid group, a family of early pseudosuchian archosaurs. This links it to the ancestral line that later gave rise to crocodilians and their relatives.
What time period did Arizonasaurus live in?
It roamed the Earth during the Middle Triassic, roughly 240 million years ago. At that time it was one of the more distinctive land-dwelling archosaurs in its ecosystem.
More in Prehistoric Extinct Animals 1-24
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