■ The ossified tendons that reinforced the tails kept them stiff, not flexible. In contrast, modern aquatic species of large reptiles, such as crocodilians, are very dependent on their flexible tails for propulsion.
■ The manus and pes of a typical iguanodontian are much too small in proportion to the rest of the body to have overcome the resistance of the water that would have dragged on their considerable bulks. This situation is regardless of whether they had webbed feet or not.
■ The hind limbs show little evidence that they were better adapted for swimming than those of similarly sized theropods. This is not to say that iguanodontians could not swim. After all, similarly bulky elephants can swim long distances. But if a primary mode of defense was to swim away from predators, they should show adaptations that are clearly superior to those of their supposed theropod harassers.
As mentioned earlier, the hollow cranial crests of lambeosaurines also were considered to be snorkel-like aquatic adaptations, but the discovery that the "snorkel" did a U-turn (and thus would have quickly caused drowning) nullified that hypothesis. Finally, the "duckbill" of hadrosaurids, with its lack of anterior teeth and its distinctive shape, so characteristic of these ornithopods, was also cited as evidence for a semi-aquatic habit. Also, soft plants typical of coastal areas and lakes were thought to be the food most suitable for these ornithopods. Such a scenario ignored these dinosaurs' impressive dental batteries, which are now recognized as among the best adaptations to feeding on tough, fibrous foods ever devised in the history of terrestrial herbivores.
However, some iguanodontian remains are found in nearshore marine or other lowland facies, which means that a few were at least proximal to water bodies. Consequently, the aquatic-ornithopod hypothesis is not completely falsified, but it is poorly supported, which means that paleontologists will conditionally accept that most ornithopods, like most dinosaurs, were terrestrial animals.
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