In relation to Peter's fantastic summary of Ichthyosaurs in art post, commenter Neil brings up the excellent point that the huge Ichthyosaurs Shonisaurus is not as fat and deep chested as is typically reconstructed. This than raises the question what does it look like?
As I've been starting work on my own Shonisaurus, I thought I'd share the answer rather than leave the point nebulous. As I've managed to get my hands on the solution.
This is the modern take on Shonisaurus' skeleton, I believe by the Royal Tyrrell Museum's resident artist Donna Sloan (but I could be wrong). I acquired it from a plaque accompanying the fossils on display at the Tyrrell, and photoshoped it into this current form (the diagram itself is unmodified, I just removed it from the photo).
The only difference (as already well said by Neil) between this and the old skool model is the number of forward ribs. The old model was missing several and thus the chest started towards the middle of what we see in this diagram.
Hope that is a help to your Shonisaurus fans out there. Though hopefully we see a few other species than just this behemoth. Happy arting everyone!