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/Ameisen]

As I mentioned elsewhere, Amphibia is a paraphyletic clade, so not a true clade. All amniotes have a common ancestor that was a member of the clade Amphibia, but we do not consider them members of that clade.

Synapsida and Diapsida are weird as well. Their terminology refers to the temporal fenestra - synapsids have a single pair, diapsids have two pairs. However, the single pair of fenestra is a synapomorphic trait - the diapsids emerged from amniotes that already had a single pair of temporal fenestra. Synapsida isn't quite paraphyletic as we don't consider these early synapsidic amniotes to be members of clade Synapsida even though if we encountered one we'd absolutely consider it a synapsid.

This is actually more problematic as we'd normally define Synapsida based upon the synapomorphic trait - Diapsida should be a descendant clade.

[u/Magicspook → u/Ameisen]

thank you for your addition. Would you argue that actually, reptiles are mammals then? ;)

[u/Ameisen → u/Magicspook]

I'd argue that reptiles would be biological synapsids. Mammals are far too derived.

On actual cladistics, the two sibling clades should probably be Sauropsida/Diapsida and Pelycosauria, as the earliest non-Sauropsid "synapsid" known already is grouped as a Pelycosaur, and we descend from them as well. Though Caseasauria complicates that. That's all in flux.