The idea of aquatic sauropods was rejected in the 1950s because their thorax would be under a column of water some 6 m or more, making it difficult or impossible to breath (Kermack, 1951). On a 1/4th the gravity Earth though, the water pressure with depth would only be 1/4th that on Earth today (P = pgh). Water pressure at 6 meters depth with 1/4th the gravity would be the same as at 1.5 meters depth today.
Elephants are known to use their trunk as a snorkel when their thorax is under 2 meters of water, https://www.elephants.com/pdf/whyelephantscansnorkel.pdf
Sauropods show a clear trend of gradual loss of positive selection, stretching throughout Cretaceous, fits with the increase in gravity making breathing at depth impossible. https://www.pnas.org/content/113/18/5036
K. H. Kermack's claim that has dictated the scientific consensus for 70 years now, fails on a reduced gravity Earth.
