Tim Donovan wrote:
Why else would an elongated snout and jaws evolve? If spinosaurs were more massive and powerful than carcharodontosaurs, and piscivory seems questionable, could they have been sauropod hunters, using their long jaws to reach the necks of titanosaurs or rebbachisaurs?
More likely, spinosaurs targeted small prey...
From Sues et al. (2002):"The skull of _Irritator_ does not appear to be well-suited for catching and processing large, resistant prey. Its structure differs from that in other large theropod dinosaurs such as _Allosaurus_ (Rayfield et al., 2001) and _Tyrannosaurus_ (Erickson et al., 1996), presumably reflecting different modes of feeding. Most likely spinosaurid theropods rapidly and forcefully seized smaller prey, which was then processed by dorsoventral motion of the head facilitated by the powerful neck musculature. (Extensive side-to-side striking movements of the head, as employed by extant crocodylians, appear unlikely in view of the narrow occiput as well as the weak development of the basal tubera.) Whereas fish formed part of the diet in at least _B. walkeri_, there is nothing to suggest that spinosaurids were exclusively or even predominantly piscivorous. Previous anatomical comparisons between the feeding apparatus of crocodylians and spinosaurid theropods were based only on superficial resemblances."
Tim