My, what big flippers you have!

Guizhouichthyosaurus tangae (Cao et Luo in Yin et al., 2000, Late Triassic) is an ichthyosaur with really big flippers derived from a sister to Phalarodon and basal to Shonisaurus popularis.

Figure 1. Guizhouichthyosaurus in situ in ventral aspect. This specimen has some of the biggest flippers among ichthyosaurs, rivaling those belonging to plesiosaurs, which makes one hypothesize a distinct mode of swimming.

Figure 1. Guizhouichthyosaurus in situ in ventral aspect. This specimen has some of the biggest flippers among ichthyosaurs, rivaling those belonging to plesiosaurs, which makes one hypothesize a distinct mode of swimming. The large number of ribs, though, along with the sinuous backbone, suggest that undulation was still used as well.

Known from several specimens, Guizhouichthyosaurus, had a long rostrum and sharp teeth (Fig. 2). When a sea creature has such large flippers the tendency is to imagine that it swam using those paddles/underwater wings. It probably had only a rudimentary tail fin, like Phalarodon or Mixosaurus.

Figure 2. Guizhouichthyosaurus tangae skull preserved in three dimensions.

Figure 2. Guizhouichthyosaurus tangae skull preserved in three dimensions. Tracing from Maisch et al. 2015.

Guizhouichthyosaurus provides clues to the ancestry of the big-fippered Shonisaurus, one of the giants among ichthyosaurs.

Figure 2. Ichthyosaur subset of the large reptile tree.

Figure 3. Ichthyosaur subset of the large reptile tree. 

Guizhouichthyosaurus is also related to the smaller-flippered and misnamed ‘Cymbospondylus’ buchseri (Sander 1989, Fig. 4), which looks a bit like a mosasaur. Now it needs a new generic name. Earlier we looked at other ichthyosaurs more recently misnamed by Sander et al. (2011).

Figure 4. 'Cymbodpondylus' buchseri did not have such large flippers, but did have a long narrow skull and robust elongate torso.

Figure 4. ‘Cymbodpondylus’ buchseri did not have such large flippers, but did have a long narrow skull and robust elongate torso.

I have previously overlooked and ignored most ichthyosaurs because I was more interested in their ancestry among Wumengosaurus, Thaisaurus and beyond to the mesosaurs. But they are a fascinating clade with some odd morphologies worth looking into.

References
Maisch M et al. 2015. Cranial osteology of Guizhouichthyosaurus tangae (Reptilia: Ichthyosauria) from the Upper Triassic of China. Journal of Vertebrate Paleontology 26(3): 588-597.
Yin G-Z, Zhou X, Cao Y, Yu Y and Lu Y 2000. A preliminary study on the early Late Triassic marine reptiles from Guanling, Guizhou, China. Geology-Geochemisty 28(3):1–23 (Chinese with English abstract).
Sander PM 1989. The large ichthyosaur Cymbospondylus buchseri sp. nov., from the Middle Triassic of Monte San Giorgio (Switzerland), with a survey of the genus in Europe. Journal of Vertebrate Paleontology 9(2): 163-173.
Sander PM, Chen X-C, Cheng L and Wang X-F 2011. Short-snouted toothless ichthyosaur from China suggests Late Triassic diversification of suction feeding ichthyosaurs. PlosOne DOI: 10.1371/journal.pone.0019480

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