Evolution: whales and hippos related? More relationships (Evolution)

by David Turell , Monday, March 26, 2018, 23:14 (2432 days ago) @ David Turell

Yes they are, but other aquatic mammals have other ancestors, and they all come with constraints:

https://www.sciencedaily.com/releases/2018/03/180326152405.htm

"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.

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"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.

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"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.

"'Many people have viewed going into the water as more freeing for mammals, but what we're seeing is that it's actually more constraining," said co-author Jonathan Payne, a professor of geological sciences at Stanford's School of Earth, Energy & Environmental Sciences (Stanford Earth). "It's not that water allows you to be a big mammal, it's that you have to be a big mammal in water -- you don't have any other options."

"Although mammals that live in water share a similarly oblong body shape, they are not closely related. Rather, seals and sea lions are closely related to dogs, manatees share ancestry with elephants, and whales and dolphins are related to hippos and other hoofed mammals.

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"From this analysis, the group found that once land animals take to the water, they evolve very quickly toward their new size, converging at around 1,000 pounds. Smaller ancestors like dog relatives increased in size more than larger ancestors like hippos to reach that optimal weight, suggesting that bigger is better for aquatic life, but only up to a point. The group points out that otters, which took to the water more recently, don't follow that trend, perhaps because many otter species still live much of their lives on land.

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"The group argues that the larger size helps aquatic mammals retain heat in water that's lower than body temperature. "When you're very small, you lose heat back into the water so fast, there's no way to eat enough food to keep up," Payne said.

"They also suggest that metabolism increases with size more than an animal's ability to gather food, putting a boundary on how big aquatic mammals can grow. "Basically, animals are machines that require energy to operate. This need for energy places hard limits on what animals can do and how big they can be," said McClain, who was a co-author on the study.

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"If otters are the exception at the small end, baleen whales prove the exception at the larger size. These whales expend much less energy on feeding than their toothed counterparts because they filter all their food, which makes them more efficient and allows them to grow larger than toothed whales.

"'The sperm whale seems to be the largest you can get without a new adaptation," Gearty said.

"'The only way to get as big as a baleen whale is to completely change how you're eating.'"

Comment: This study supports my contention that this is a strange and difficult way to evolve with all the new reasons shown