Monday, May 10, 2010


Arizonasaurus babbitti. Scale bar = 0.5 meters. (Nesbitt 2005)

Meaning: "Arizona lizard"
Species: A. babbitti
Nominal Author: Welles 1947
Age: early Middle Triassic (Anisian - 240 Ma)
Location: Arizona, southwestern USA (Moenkopi Formation)
Physical Characteristics: a large (3+ meters) sail-backed predator (Rauisuchian)

Arizonasaurus was the dominant predator of the Moenkopi fauna, which represented an important transition into a modern fauna of crocodiles, dinosaurs(birds), mammals, lizards, and turtles, as opposed to the previous fauna, dominated by more primitive tetrapods (Nesbitt 2003). Arizonasaurus helps to close the gap between the primitive fauna of the Lower Triassic and the more modern fauna of the Upper Triassic. The type specimen for Arizonasaurus consisted solely of a mostly complete left maxilla (Welles 1947), but the far more complete skeleton found by Nesbitt in 2002 has helped to resolve relationships between fragmentary and more complete taxa within Rauisuchia.

Rauisuchian Phylogenetics:
The holotype of Arizonasaurus babbitti has been considered a dinosaur, a stagonolepid, a rauisuchian, a proterosuchian, a trilophosaurid, and a erythrosuchid, but the new remains discovered by Nesbitt suggest that Arizonasaurus is indeed a poposaurid (Hunt 1993, Nesbitt 2003). A more recent archosaur phylogeny places Arizonasaurus within Poposauroidea (bootstrap <50/4) which, combined with its sister taxon Rauisuchoidea, makes up Rauisuchia (Brusatte et al 2010). Within Poposauroidea, resolution decreases, resulting in a polytomy between Arizonasaurus, Bromsgroveia, Lotosaurus, Poposaurus, Sillosuchus, and Shuvosauridae (Effigia + Shuvosaurus). When ankle characters were removed, Arizonasaurus and Bromsgroveia were united into a single taxon.


  1. One of the strangest prehistoric "crocs", that's for sure... Any idea why he developed that sail-like structure on his back?

  2. Well, I would have to look into it a lot further, but my first guess would be for thermoregulatory purposes, like the mid-Cretaceous dinosaurs Spinosaurus, Ouranosaurus, and Amargasaurus. I'll have to look into the paleoclimatology of the early Middle Triassic tho. Such structures have also been suggested to have been used for display.

  3. Yeah, i think that's the most plausible theory about those structures ;)

  4. Don't forget the Permian synapsid Dimetrodon! Also, Bullyland makes a pretty sweet Arizonasaurus figure. I have one somewhere.

  5. And Edaphosaurus! So many cool sail-backs.

  6. I think the sail on its back was used mostly for display, but also thermoregulatory purposes.

  7. I think spinosaurus is the coolest

  8. You got to look up liopleurodon.

  9. I have an unusual fantasy about the sails. They would have been multifunctional not just one function. The sails are common in aquatic dinosaurs such as spinosaurus that mostly stayed in the water. If an animal is submerged if they explosively lurch over to the side the sail would give them far better reach when the neck lunged over because the sail would give a base of resistance against the water. An animal without the sail when lurching over to grab--in that movement half of the grab distance would be lost because the entire body would shift. Now picture spinosaurus was placed underwater and you hook up some braces to him on one side. now when he lurches over to grab a fish MOST of the movement is actual reach. With the swim tracks scratch marks on the bottom showing up prove that many of them were alot more aquatic than we thought. Alligators and crocs can sit on the bottom often deep down for HOURS however in the drawings they arent pictured like that they are pictured laying around on the surface next to the water-when in fact when feeding almost all of their time is in the water. Thermo regulation yes but according to the physics--if in water the sail WOULD increase their grab distance. I suggest "multifunctional" and spinosaurus that ate fish is the best example. The sail would also help spinosaurus and the others if they lounged in water possibly cold in that the sail would be exposed to the warm sun letting them lie in wait for longer periods. So it could be a combination of SEVERAL things. Why then dont gators have a sail?--I simply dont know.