Giant sauropod dinosaurs were too heavy to support themselves on land and therefore had to live largely submerged in water.

Sauropods reached sizes unlike any living land animal, and for much of the late 19th and early 20th centuries many paleontologists thought their bodies were too heavy to support on land. Reconstructions therefore placed them in lakes and swamps, where buoyancy could carry much of their weight while their long necks reached the surface.

The idea was never universal. Elmer Riggs and other paleontologists argued early in the 20th century that sauropods were capable terrestrial animals, but the aquatic image remained influential for decades.

Evidence increasingly favored life on land. Trackways recorded enormous sauropods walking across terrestrial surfaces, while their column-like limbs, feet, vertebral column, and weight-bearing joints were well suited to supporting large bodies. Walter Coombs’s 1975 review brought anatomical and sedimentological evidence together and concluded that sauropods were primarily terrestrial.

Later biomechanical modelling added another problem for the swamp model. Sauropods had extensive air spaces in their skeletons and probably bird-like respiratory air sacs. That pneumaticity would make them highly buoyant and potentially unstable when deeply immersed rather than allowing them to stand comfortably on the bottom.

Sauropods could still enter water, wade, and probably swim. What was overturned was the need for water to support their size. Their skeletons were adapted to carrying their enormous bodies on land.