Most dinosaurs were terrestrial, but there were a couple of groups of arboreal and flying dinosaurs (microraptors, birds etc).
I have read that the theory that Brachiosaurids were aquatic has been largely discredited1, but that Spinosaurids were probably semi-aquatic2.
Excluding modern marine birds (e.g. penguins etc.), were there any other marine/aquatic dinosaurs?
Note: I am aware that the marine reptiles mesosaurs, phytosaurs, mosasaurs, dolichosaurs, Icthyosaurs, thalattosaurs, Sauropterygia (placodonts, nososaurs, plesiosaurs etc), Choristodera were not part of Dinosauria.
• Three new sauropod dinosaurs from the Upper Jurassic of Colorado, Great Basin Naturalist.
• The Physiology of Dinosaurs: Circulatory and Respiratory Function in the Largest Animals Ever to Walk the Earth, Respiratory Care
• A note on the habits of sauropods, Annals and Magazine of Natural History
• Tipsy punters: sauropod dinosaur pneumaticity, buoyancy and aquatic habits, Proceedings of the Royal Society of London
• Oxygen isotope evidence for semi-aquatic habits among spinosaurid theropods, Geology
• Semiaquatic adaptations in a giant predatory dinosaur, Science
• Convergent evolution of jaws between spinosaurid dinosaurs and pike conger eels, Acta Palaeontologica Polonica
• Functional Morphology of Spinosaur ‘crocodile-Mimic’ Dinosaurs, Journal of Vertebrate Paleontology