Shastasaurus postcrania

Earlier we looked at many of the taxa that have been attributed to Shastasaurus (Late Triassic, Norian, 210 mya).

And then a closer look at the two shastasaurs, including the holotype, nesting as basal ichthyosaurs — and unexpectedly as basal to hupehsuchids (based on traits used in the large reptile tree, not ichthyosaur specific traits).

I was finally able to find data
on Shastasaurus alexandrae post-crania with scale bars (Fig. 1) from a paper in which a specimen of Guizhouichthyosaurus was falsely attributed to Shastasaurus (Shang and Li 2009). These elements permit the reconstruction of the specimen and comparison to other specimens to scale (Figs. 1, 2).

Figure 1. Shastasaurus alexandrae, including scaled post-crania. Length of torso and tail unknown.

Figure 1. Shastasaurus alexandrae, including scaled post-crania. Length of torso and tail unknown. Note the lack of phalanges for the manus and pes. Note the open acetabulum. Wikipedia indicates that Shastasaurus specimens might have measured up to 21 meters (69 feet). That may refer to the giant ‘Shonisaurus’ sikanniensis.  This specimen is considerably smaller at 3 meters. 

There are many more specimens attributed to S. alexandrae and they can be accessed here and here at the UC Berkeley paleontological collection.

Figure 2. The two shastasaurs to scale. The differences in these sister taxa are subtle. Their sizes are comparable.

Figure 2. The two shastasaurs to scale. The differences in these sister taxa are subtle. Their sizes are comparable.

In the Berkeley collection 
there are many partial specimens attributed to Shastasaurus. Some of these specimens have flippers that are very much like those of Shonisaurus. Those specimens may in fact be more closely related to Shonisaurus, which is a taxon not related to Shastasaurus.

The above two specimens of Shastasaurus nest close to the base of the Ichthyopterygia. To shift them to Shonisaurus adds 27 steps to the large reptile tree.

Wikipedia notes: 
“If S. sikkanniensis belongs to Shastasaurus, it would be the largest species, measuring up to 21 metres (69 ft).” In the large reptile tree ‘S’. sikanniensis is not closely related to Shastsaurus.

Something of a mess here.
Could use a PhD candidate to clean things up. It is so important to discuss and test specimens — not make chimaeras, juveniles and adults of multiple specimens.

References
Merriam JC 1895. On some reptilian remains from the Triassic of Northern California. Amer. J. Sci., (3), 50: 55–57; New Haven.
Shang Q-H and Li C 2009. On the occurrence of the ichthyosaur Shastasaurus in the Guanling biota (Late Triassic), Guizhou, China. Vertebrata PalAsiatica 47(3):178-193.

 

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