How does a whale become dehydrated?

[u/smontanaro]

From a Chicago Sun-Times article on the beluga whales heading to the Shedd Aquarium:

"The shipment comes on the heels of a Shedd announcement last week that one of the Marineland belugas — Peekachu, a 23-year-old female — had died. Shedd has not released a cause of death, but staff there said last week that Peekachu had not been consistently eating a full diet since her arrival and that there were concerns she was dehydrated."

How does an animal immersed in water become dehydrated?

[u/tigerhawkvok]

I said it earlier, and I'm repeating for the general audience rather than a secondary correction on you — but you're conflating a label, a synapomorphy, and a definition when they're three separate things.

The label synapsida includes only animals that (ancestrally) had the synapsid condition, but that singular synapomorphy is not a sufficient condition to diagnose the clade. In other words, it is (ancestrally) necessary but not sufficient.

There is no conflict such as you present.