A new ichthyosaur mimic: Sclerocormus

A new Nature paper
by Jiang et al. 2016 introduces Sclerocormus, a large sister to the much smaller Cartorhynchus. Like a marine Cotylorhynchus, this odd basal sauropterygian had a tiny skull not much larger than that of its much smaller, big-headed sister (Fig. 1).

Figure 1. Large Sclerocormus and its much smaller sister, Cartorhynchus. These nest with basal sauropterygians, not ichthyosauriforms.

Figure 1. Large Sclerocormus and its much smaller sister, Cartorhynchus. These nest with basal sauropterygians, not ichthyosauriforms. Click to enlarge. Note the skull size of the two are within a short range.

These two nested
with Qianxisaurus, a basal sauropterygian/pachypleurosaur, not basal ichthyosauriforms. The authors are still in the dark about ichthyosaur ancestors. You can trace them, or any taxon, back to basal tetrapods here.

Figure 1. Although the pectoral girdle was preserved just behind the skull, in all sister taxa there are about 19 cervicals and 19 dorsals. Plus the pectoral girdle itself is very wide, better suited to the widest ribs. Perhaps Cartorhynchus had a longer neck than commonly assumed.

Figure 2. Although the pectoral girdle was preserved just behind the skull, in all sister taxa there are about 19 cervicals and 19 dorsals. Plus the pectoral girdle itself is very wide, better suited to the widest ribs. Perhaps Cartorhynchus had a longer neck than commonly assumed.

The authors
report that Sclerocormus had no teeth and that the nasals extended to the tip of the rostrum. I have to disagree with both observation given the photographic data and lack of similarity in sister. They also misidentified a few bones. Their big scapula is a posterior coronoid + smaller scapula.

More coming in later posts.

References
Jiang D-Y, Motani R, Huang J-D, Tintori A, Hu Y-C, Rieppel O, Fraser NC, Ji C, Kelley NP, Fu W-L and Zhang R 2016. A large aberrant stem ichthyosauriform indicating early rise and demise of ichthyosauromorphs in the wake of the end-Permian extinction. Nature Scientific Reports online here.

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