Shonisaurus lived during the Norian stage of the late Triassic period (215 mya). S. popularis measured around 15 metres (49 ft) long. A second species from British Columbia was named Shonisaurus sikanniensis in 2004. S. sikkanniensis was one of the largest marine reptiles of all time, measuring 21 metres (69 ft). However, phylogenetic studies later showed S. sikanniensis to be a species of Shastasaurus rather than Shonisaurus.
Shonisaurus and Shastasaurus may have specialized on eating shell-less cephalopods, as adult specimens appear to lack teeth entirely, a trait that is not found in most other ichthyosaur species.
A unique fossil bed of these massive marine reptiles led paleontologists to hypothesize that an equally massive octopus ancestor, or “Triassic Kraken,” may have killed the Shonisaurs and arranged them in a particular pattern. Modern-day octopods are known to create middens using prey items, so the idea is not entirely unfounded. The scientists have gone as far as to suggest that this ancient Shonisaurus midden may have been created as a sort of octopod “self-portrait” indicating that the ancient kraken may have been an intelligent being. An alternative (perhaps more likely) theory suggests that the midden may be a sexually selected trait in the ancient octopod species.
Learn more about the kraken midden here.
Learn more about the Shonisaurus here.