Why were sauropods once thought to live in shallow water?

Historically, scientists hypothesized that sauropods were swamp or lake dwellers primarily because they believed their massive bodies were too heavy to be supported by their legs on solid ground. This assumption was reinforced by the discovery of early specimens in aquatic sediments, leading 19th-century biologist Richard Owen to misidentify them as giant aquatic crocodiles.12

However, this "amphibious" theory has been debunked by modern research:

• Structural Capacity: Experiments with fresh bone samples demonstrate that sauropod limb bones were fully capable of supporting their immense weight on land.1
• Physical Constraints: The laws of hydrostatic pressure indicate that a long-necked animal submerged in deep water would be unable to expand its lungs to breathe, as atmospheric pressure would be insufficient at those depths.1
• Evidence of Terrestrial Life: Extensive trackway sites confirm that these dinosaurs navigated on land, and their skeletal anatomy shows no specialized features for an aquatic existence.12

Today, sauropods are understood to have been successful terrestrial browsers, using their long necks to reach foliage in a manner similar to modern giraffes.12