Being entirely naive to squid prehistory, the wikipedia page for squid shows two apparent-to-me squid fossils [0]. Is there some nuance here that I'm not aware of?

[0] https://en.wikipedia.org/wiki/Squid#Evolution

Not sure about squids in particular, but the easiest way isn't necessarily to find remains, but to see negative prints on sediments.

Tons of fossils are "negative prints on sediments". GP's assertion that "If humans didn't exist while they do, we would have never known about them" is clearly wrong.

Have you considered just budgeting yourself $600/month on guilt-free non-essential transportation, and committing to spending any remainder on nice refreshments/gifts for your friends?

I read it as the students being familiar with a similar "trick" question and erroneously pattern matching on that.

Another similar riddle goes like:

"If it takes 5 machines 5 minutes to make 5 widgets, how long would it take 100 machines to make 100 widgets?"

The correct answer there being "5 minutes", and the intuitive wrong answer being "100" as per your post.

That would make sense as to why the teacher also expected "3", since they should be familiar with the existence of their non-intuitive questions, even if they misremember the specific non-intuition.

Or as to why adding more people to a late project makes it later: 1 woman takes 9 months to grow a baby, how long does it take 9 women to grow a baby?

The video game "To The Moon" and its sequels/related media explores this premise.