ScienceDaily recently posted an article that tries to answer this question. The article begins as follows:
“Anyone who has witnessed majestic whales or lumbering elephant seals in person would be forgiven for associating ocean life with unlimited size in mammals, but new research reveals that mammal growth is actually more constrained in water than on land.
This finding by Stanford researchers is in contrast to previous theories suggesting that pressure on body size should be more relaxed in water, perhaps because of the large environment and ability for animals to float rather than have to support their body weight on legs.
Instead, the group found that aquatic mammal size is bounded at the small end by the need to retain heat and at the large end by difficulties getting enough food to survive. The group published their findings March 26 in Proceedings of the National Academy of Sciences.”
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