Mosasaurus chasing a shark (yes, a variant of the famous Jurassic World poster, but the Mosasaurus looks more like it should in this and also has the right size). ZBrush, Keyshot and a bit of Photoshop at the end.
/Anders
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This is just amazing.
Wonderful work 
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Regards Jacek
Agreed, this is amazing. I love the ocean bound dinosaurs so this is a spectacular render. Great work!
Great job - wonderful curves and flow to your piece.
wow
Great work.It is shown underwater environment perfectly.
Is it possible you can tell more about the caustic effect? I am trying to get an underwater effect from Keyshot - but no really luck?
Ps: amazing result you ended up with 
Well, as far as I can recall the water surface is dielectric with a bump map of waves (setting noise (fractal)), same refraction index as water.
/Anders