Shastasaurus liangae

Fig 1.- Shastasaurus sikanniensis is the largest known ichthyosaur with an estimated length of some 20 meters.

A new paper published in PLoS by P. Martin Sander and co-workers, just made the  ichthyosaurs an even more interesting and intriguing prehistoric critters. Ichthyosaurs are a group of extinct marine reptiles with streamline fish-like bodies that roamed the oceans from the Early Triassic to the Early Cretaceous periods.

A well-preserved specimen of the species previously described as Guanlingsaurus liangae from the Late Triassic of China shed light to a peculiar group of medium to large size ichthyosaurs called Shastasauridae. 

 
Compared to the standard body shape of ichthyosaurs (think Ophthalmosaurus of WWD fame), the new specimen is characterized by a diminutive head, with an entirely toothless and greatly reduced snout. The description of this new specimen led to a general revision of the genus Shastasaurus, based on S. pacificus from the Late Triassic of California, to include not only G. liangae (re-baptized S. liangae) but also the largest known ichthyosaur, S. sikanniensis (formerly Shonisaurus sikanniensis) from the Late Triassic of British Columbia.

Fig 2.- The medium size Shastasaurus liangae may have hunted bioluminescent squids in the deep sea using the technique of suction feeding, similarly to some modern Odontocete cetaceans.
 

The peculiar skull anatomy of S. liangae lead the authors of the study to hypothesize that the three species of Shastasaurus were specialized suction feeder that preyed on squids and fish. The relative rarity of Shastasaurus fossils as well as their association with fully pelagic invertebrates, indicates a pelagic lifestyle. An interesting idea suggested by the authors is that their relatively large eyes would have been perfect to hunt bioluminescent cephalopods in the deep sea.

References:

Nicholls EM, Manabe M (2004) Giant ichthyosaurs of the Triassic-A new species of Shonisaurus from the Pardonet Formation (Norian, Late Triassic) of British Columbia. Journal of Vertebrate Paleontology 24: 838–849.

Sander PM, Chen X, Cheng L, Wang X (2011) Short-Snouted Toothless Ichthyosaur from China Suggests Late Triassic Diversification of Suction Feeding Ichthyosaurs. PLoS ONE 6(5): e19480.

Yin G, Zhou X, Cao Z, Yu Y, Luo Y (2000) A preliminary study on the early Late Triassic reptiles from Guanling, Guizhou, China (in Chinese). Geology- Geochemistry 28: 1–23.