What is Azendohsaurus?

Updated May 15, 2015 to reflect the new nesting of Azendohsaurus back with Trilphosaurus.

Azendohsaurus has bounced around the reptile family tree.
Azendohsaurus was originally described by Dutuit (1972) as an ornithischian dinosaur on the basis of two teeth and a dentary fragment. Gauffre (1993) found a bit more of the dentary and described Azendohsaurus as a prosauropod. Flynn et al. (2010) found a relatively complete skeleton in Madagascar, but only the skull has been published to date. Flynn et al. (2010) considered Azendohsaurus the “nearest archosauromorph outgroup to the archosauriformes (but then they also ascribe to the false nesting of Trilophosaurus and rhynchosaurs as sisters to Archosauriformes).

Figure 1. The skull and palate of Azendohsaurus, a sister to Trilophosaurus. 

Figure 1. The skull and palate of Azendohsaurus, a sister to Trilophosaurus.

Nesting Azendohsaurus on The Large Reptile Family Tree
Here, phylogenetic analysis nests Azendohsaurus with Trilophosaurus, a lepidosaur (Fig. 2).

Figure 2. DGS applied to the skull of Azendohsaurus. Note the new addition of a lateral naris, not previously noted.

Figure 2. DGS applied to the skull of Azendohsaurus. Note the new addition of a lateral naris, not previously noted. Compared to sister taxa, both the ascending processes of the premaxilla and maxilla are very tall. 

Teeth
In Trilophosaurus two rows of teeth are present but fused to form wide teeth with two roots. Azendohsaurus is similar with two rows of large teeth (on the maxilla and palatine) growing close to one another. Flynn et al. (2010) reported that the palatine was reversed from what is shown in figures 1 and 2, with a toothless anterior maxillary process.

Convergence with Sauropods
The elevation and reduction of the naris converges with that of sauropods and gives Azendohsaurus it’s sauropod-like look. Flynn et al. (2010) reported, “Azendohsaurus and numerous basal sauropodomorph dinosaur taxa share an array of convergently acquired features associated with herbivory, including tooth denticles, expanded tooth crowns, a downturned dentary and the articular located at the ventral margin of the mandible.”

Nesbitt et al. 2013. reported on the post-crania:
“Azendohsaurus madagaskarensis possessed an elongated neck, short tail, and stocky limbs. The manus and pes have unexpectedly short digits, terminating in large, recurved ungual phalanges. Together with the skull, knowledge of the postcranial skeleton elevates A. madagaskarensis to another highly apomorphic and bizarre Triassic archosauromorph.”

This description is both distinct and similar to Trilophosaurus.

References
Dutuit J-M 1972. Découverte d’un Dinosaure ornithischien dans le Trias supérieur de l’Atlas occidental marocain. Comptes Rendus de l’Académie des Sciences à Paris, Série D 275:2841-2844.
Flynn JJ, Nesbitt, SJ, Parrish JM, Ranivoharimanana L and Wyss AR 2010. A new species of Azendohsaurus (Diapsida: Archosauromorpha) from the Triassic Isalo Group of southwestern Madagascar: cranium and mandible”. Palaeontology 53 (3): 669–688. doi:10.1111/j.1475-4983.2010.00954.x
Gauffre, F-X 1993. The prosauropod dinosaur Azendohsaurus laaroussii from the upper Triassic of Morocco. Palaeontology 36(4):897-908. Gauffre pdf online
Nesbitt, S, Flynn J, Ranivohrimanina L, Pritchard A and Wyss A 2013. Relationships among the bizarre: the anatomy of Azendohsaurus madagaskarensis and its implications for resolving early archosauromroph phylogeny. Journal of Vertebrate Paleontology abstracts 2013.

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