Madagascar. This bizarre island is just made for dinosaur extremes. Situated as an island off the coast of Africa for millions of years since its separation from the African and Asian continents, the animals that have lived and gone past on that island are all unique, interesting, and extremely well adapted to their lives on the island. The dinosaurs were no different; consider three that have been discussed lately: Majungasaurus, Masiakasaurus, and Rapetosaurus. They all have unique features making them well suited to perform admirably in their environmental niche and they thrived on their small island for a good amount of time. Masiakasaurus was pretty average compared to the other two dinosaurs until its lower jaw, the dentary bones, were discovered.
The body overall is pretty darn typical until you get to that skull, then there is that jaw full of teeth which are astoundingly strange and interesting. The teeth come nearly straight out of the lower jaw at the extreme front and make a basket like structure with the front top teeth. This unique tooth type and arrangement is seen in spinosaurs and to a lesser degree in the dinosaur Baryonyx; all of which are thought to be piscivorous dinosaurs. Comparing the jaws there is one other aspect of the Masiakasaurus which sticks out other than its front teeth. The jaws of Baryonyx, Spinosaurus, and the crocodile skull at left are much longer than they are deep and, though they all contain a certain amount of robustness to their physique, they are generally fairly thin top to bottom with the general shape of a heron type beak if we were to compare it to birds which makes it a near perfect shape for stabbing into water to catch fish, frogs, whatever else. We know crocodile diet is not entirely fish, and I assume Spinosaurus and Baryonyx were also not entirely fish eating all the time. However, the skull of Masiakasaurus, though not all has been found still, is clearly much more robust top to bottom and is shaped more like your average theropod's skull. It is elongate to a degree, though the degree of elongation is nowhere near as prominent as the other assumed fish eating dinosaurs.