Thesaurus - is this deliberate?

[Shenstone]

I was looking at the standard Thesaurus that I know is just a starting point and I noted this and I wondered whether it's deliberate to demonstrate something 

The ones in yellow are under mammals, but are not mammals 
Then there is a seperate entry for marine mammals 

Just checking in case I have missed something 

Regards Andy

[Mario]

Not sure why this is, I frankly haven't looked at the default thesaurus for years. I'll have a look.
You can delete this branch or move it to wherever you prefer.

[Shenstone]

Many thanks - I'm learning, I just wanted to understand that it wasn't for some complex reason I didn't understand

Regards Andy

[sybersitizen]

The ones in yellow are under mammals, but are not mammals
Then there is a seperate entry for marine mammals

My thesaurus also had that structure. Most of Marine Life should be moved out of where it is and placed as a child of Animals & Pets instead, leaving Dolphins, Manatees, and Whales under Marine Mammals. I first tried to drag and drop some things, but that didn't appear to have any effect. I ended up cutting and pasting as needed (after exporting the thesaurus in case something bad might happen). Seems okay now.