Arizonasaurus

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Arizonasaurus
Temporal range: Middle Triassic, 243Ma
Arizonasaurus BW.jpg
Arizonasaurus babbitti
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Paracrocodylomorpha
Branch: Poposauroidea
Family: Ctenosauriscidae
Genus: Arizonasaurus
Welles, 1947
Species
  • A. babbitti Welles, 1947 (type)

Arizonasaurus was a ctenosauriscid archosaur from the Middle Triassic (243 million years ago).[1] Arizonasaurus is found in the Middle Triassic Moenkopi Formation of northern Arizona. A fairly complete skeleton was found in 2002 by Sterling Nesbitt. The taxon has a large sailback formed by elongate neural spines of the vertebrae. The type species, Arizonasaurus babbitti, was named by Samuel Paul Welles in 1947.

Discovery and naming[edit]

The type species, Arizonasaurus babbitti, was named by Samuel Paul Welles in 1947 on the basis of a few teeth and a maxilla, labelled as specimen UCMP 36232.[2] A fairly complete skeleton was found in 2002 by Sterling Nesbitt.[3]

Description[edit]

It had a sail made of tall neural spines, that was similar to those of other basal archosaurs like Ctenosauriscus, Lotosaurus, Bromsgroveia, and Hypselorhachis.[4]

Braincase[edit]

Arizonasaurus is described from two specimens of braincases. Some ancestral features of the braincase of Arizonasaurus are plesiomorphic for crurotarsans.[1]

Distinguishing characteristics[edit]

Below is a list of characteristics found by Nesbitt in 2005 that distinguish Arizonasaurus:[4]

  • a deep fossa hidden from view on the posteroventral edge of the upward-pointing process of the maxilla;
  • and a tongue-groove attachment between the pubis and the ilium.

Classification[edit]

Arizonasaurus was closely related to Ctenosauriscus, and together with a few other genera they make up Ctenosauriscidae. The ctenosauriscids were closely related to the poposaurids, as shown by a few shared derived characteristics.[3] The pelvic girdle in Arizonasaurus unites this taxon with Ctenosauriscus, Lotosaurus, Bromsgroveia, and Hypselorhachus.[4] Together, newly identified pseudosuchian features act as evidence that poposaurids, like Poposaurus, Sillosuchus, and Chatterjeea, and ctenosauriscids form a monophyletic group and are both derived rauisuchians.[3]

Below is a phylogenetic cladogram by Butler et al. in 2011 showing the cladistics of Archosauriformes, focusing mostly on Pseudosuchia:[5]


Mesosuchus




Prolacerta


Archosauriformes

Proterosuchus




Erythrosuchus




Vancleavea





Tropidosuchus



Chanaresuchus





Euparkeria





Parasuchus




Smilosuchus



Pseudopalatus




Archosauria
Pseudosuchia


Riojasuchus



Ornithosuchus



Suchia

Gracilisuchus



Turfanosuchus




Revueltosaurus




Aetosaurus




Stagonolepis



Longosuchus







Ticinosuchus


Paracrocodylomorpha
Poposauroidea

Qianosuchus



Ctenosauriscidae

Arizonasaurus



Xilousuchus



Hypselorhachis



Ctenosauriscus



Waldhaus Taxon






Poposaurus gracilis H



Poposaurus gracilis Y





Lotosaurus




Sillosuchus




Shuvosaurus



Effigia








Loricata

Prestosuchus




Saurosuchus




Batrachotomus




Fasolasuchus





Rauisuchus




Polonosuchus silesiacus



Postosuchus alisonae



Postosuchus kirkpatricki




Crocodylomorpha

CM 73372




Hesperosuchus agilis



Hesperosuchus "agilis"



Dromicosuchus



Alligator














Avemetatarsalia










Biogeography[edit]

Arizonasaurus is from the middle Triassic Moenkopi Formation of northern Arizona. The divergence of birds and crocodiles occurred earlier than previously thought, as the presence of a poposaurid in the early Middle Triassic suggests. Ctenosauriscids from the Middle Triassic allow the distribution of Triassic faunas to be more widespread, now in Europe, Asia, North America and Africa. The fauna of the Moenkopi Formation represent a stage transitional fauna between faunas of older and younger age.[3]

References[edit]

  1. ^ a b Gower, D.J. & Nesbitt, S.J. (2006). "The braincase of Arizonasaurus babbitti-further evidence for the non-monophyly of ‘rauisuchian’ archosaurs". Journal of Vertebrate Paleontology 26 (1): 79–87. doi:10.1671/0272-4634(2006)26[79:TBOABE]2.0.CO;2. 
  2. ^ Welles, S.P. (1947). "Vertebrates from the Upper Moenkopi Formation of northern Arizona". University of California Publications in Geological Sciences 27 (7): 241–294. 
  3. ^ a b c d Nesbitt, S.J. (2003). "Arizonasaurus and its implications for archosaur divergence". Proceedings of the Royal Society B. 270: S234–S237. doi:10.1098/rsbl.2003.0066. PMC 1809943. PMID 14667392. 
  4. ^ a b c Nesbitt, S.J. (2005). "Osteology of the Middle Triassic pseudosuchian archosaur Arizonasaurus babbitti". Historical Biology 8 (1): 19–47. doi:10.1080/08912960500476499. 
  5. ^ Butler, R.J.; Brusatte, S.J.; Reich, M.; Nesbitt, S.J.; Schoch, R.R. & Hornung, J.J. (2011). Andrew A. Farke, ed. "The Sail-Backed Reptile Ctenosauriscus from the Latest Early Triassic of Germany and the Timing and Biogeography of the Early Archosaur Radiation". PLoS ONE 6 (10): e25693. doi:10.1371/journal.pone.0025693. PMC 3194824. PMID 22022431. 

External links[edit]