Hi, this is the first time I write a critique but I hope it can help you. Concept is super nice, and composition would be as well, but I think you need more air above, it'd be solved adding canvas in the upper side. The action of the water and the view of the character, are asking for space there, so the focus of the action is not lost outside the canvas. Also, if the tail of the dinosaur was higher or lower, you'd avoid the same level with the mountain of the back. I think the sketch is lovely by the way And the style of the feet of the guy is funny. I like it!