A recent interpretation of the fossil remains of the enigmatic, large predatory dinosaurSpinosaurus aegyptiacusStromer 1915 proposed that it was specially adapted for a semi-aquatic mode of life—a first for any predatory dinosaur. To test some aspects of this suggestion, a three-dimensional, digital model of the animal that incorporates regional density variations, lungs and air sacs was generated, and the flotation potential of the model was investigated using specially written software. It was found thatSpinosauruswould have been able to float with its head clear of the water surface, although it was laterally unstable and would tend to roll onto its side. Similarly detailed models of another spinosauridBaryonyx(Suchomimus)tenerensisSereno et al. 1998, along with models of the more distantly relatedTyrannosaurus rexOsborn 1905,Allosaurus fragilisMarsh 1877,Struthiomimus altusLambe 1902, andCoelophysis bauriCope 1887 were also able to float in positions that enabled the animals to breathe freely, showing that there is nothing exceptional about a floatingSpinosaurus. Validation of the modelling methods was done with floated models of an alligator and an emperor penguin. The software also showed that the center of mass ofSpinosauruswas much closer to the hips than previously estimated, similar to that observed in other theropods, implying that this dinosaur would still have been a competent walker on land. With its pneumatised skeleton and a system of air sacs (modelled after birds), theSpinosaurusmodel was found to be unsinkable, even with its lungs deflated by 75%, and this would greatly hinder a semi-aquatic, pursuit predator. The conclusion is thatSpinosaurusmay have been specialized for a shoreline or shallow water mode of life, but would still have been a competent terrestrial animal.