Maybe Asilisaurus had shorter arms
Figure 1. Asilisaurus. Above: as reconstructed by Nesbitt et al. (2010). Below: With shorter arms, more in accord with the thickness of the bones. The related Lotosaurus was a quadruped and had much more robust forelimbs. Other sister taxa had relatively short arms.
How Long Were the Arms of Asilisaurus?
Asilisaurus (Nesbitt et al. 2010) is a basal dinosaur with incomplete forelimbs. It was originally reconstructed with long forelimbs in a quadrupedal configuration (Fig. 1). The question is: were the arms reconstructed too long? The humerus includes both ends but has a broken middle. The ulna/radius does not include the proximal ends.
Asilisaurus is the oldest known reptile in the dinosaur lineage, according to Nesbitt et al. (2010) and Wikipedia, but the large reptile tree finds Lotosaurus* is also a dinosaur that is just as old. Both lived during the Anisian period of the Middle Triassic (245-237 mya). Asilisaurus is a sister to Silesaurus in alll studies.
Considering only the Nesbitt drawings (my only data), it appears that the fore limbs may have been drawn too long in order to force a quadrupedal configuration. Why not let the bone diameters help determine their lengths? Moreover, sister taxa, like Pisanosaurus and Poposaurus, had short forelimbs. Silesaurus may have been bipedal. Lotosaurus was a sister taxon with robust forelimbs and a quadrupedal configuration. If Asilisaurus were indeed quadrupedal more robust forelimbs might be expected following these patterns. Even Pisanosaurus has more robust forelimbs.
*Nesbitt (2007) suggested Lotosaurus was a poposaurid, more closely related to Shuvosaurus, not to Xilosuchus, but in the same large clade of rauisuchians. The large reptile tree nested poposaurids within the Dinosauria, but Xilosuchus and Arizonasaurus, the other two finbacks, with the rauisuchids.
As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.
Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.
References
Nesbitt SJ, Sidor CA, Irmis RB, Angielczyk KD, Smith RMH and Tsuji LMA 2010. Ecologically distinct dinosaurian sister group shows early diversification of Ornithodira. Nature 464 (7285): 95–98. doi:10.1038/nature08718. PMID 20203608.
2012-08-15 19:02:34
Source: http://pterosaurheresies.wordpress.com/2012/08/16/maybe-asilisaurus-had-shorter-arms/
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